[RFCv6 PATCH 00/18] Checkout aware of Submodules!

[RFCv6 PATCH 00/18] Checkout aware of Submodules!

[Stefan Beller]

previous work:
https://public-inbox.org/git/20170223225735.10994-1-sbeller@google.com/
https://public-inbox.org/git/20161203003022.29797-1-sbeller@google.com/

v6:
 * added support for read-tree (see last patch) to see how generic the
   code of the previous patches is. I am pretty pleased with that patch.
 * marked two functions static. Thanks Ramsay!
 * fixed the recursive test; it still fails but it is the code that fails,
   not the test. For this I had to change the setup code slightly.
 * 2 new patches adding tiny refactoring to the submodule test lib.  
 * interdiff (to origin/sb/checkout-recurse-submodules, which is v5) below.

v5:
 * as v4 was the first version queued by Junio, we do have an interdiff below!
 * renamed functions
 * changed the API, now the caller has to take care of the submodule strategy
   themselves. (Note this can be different for different situations, e.g.
   when a submodule is deleted, we can do that for any strategy except none and
   !command. But for moving to a new state of the submodule we currently
   only implement "checkout" [unspecified defaults to checkout]. warning about
   the others, doing nothing there.)

v4:
 * addressed all comments of Brian, Junio and Brandon.
 Thanks!
 * one major point of change is the introduction of another patch
   "lib-submodule-update.sh: do not use ./. as submodule remote",
   as that took some time to track down the existing bug.
 
v3:
 * moved tests from t2013 to the generic submodule library.
 * factored out the refactoring patches to be up front
 * As I redid the complete implementation, I have the impression this time
   it is cleaner than previous versions.
 
 I think we still have to fix the corner cases of directory/file/submodule 
 conflicts before merging, but this serves as a status update on my current
 way of thinking how to implement the worktree commands being aware of
 submodules.
 
Thanks,
Stefan

v2:
* based on top of the series sent out an hour ago
  "[PATCHv4 0/5] submodule embedgitdirs"
* Try to embed a submodule if we need to remove it.
* Strictly do not change behavior if not giving the new flag.
* I think I missed some review comments from v1, but I'd like to get
  the current state out over the weekend, as a lot has changed so far.
  On Monday I'll go through the previous discussion with a comb to see
  if I missed something.
  
v1:
When working with submodules, nearly anytime after checking out
a different state of the projects, that has submodules changed
you'd run "git submodule update" with a current version of Git.

There are two problems with this approach:

* The "submodule update" command is dangerous as it
  doesn't check for work that may be lost in the submodule
  (e.g. a dangling commit).
* you may forget to run the command as checkout is supposed
  to do all the work for you.

Integrate updating the submodules into git checkout, with the same
safety promises that git-checkout has, i.e. not throw away data unless
asked to. This is done by first checking if the submodule is at the same
sha1 as it is recorded in the superproject. If there are changes we stop
proceeding the checkout just like it is when checking out a file that
has local changes.

The integration happens in the code that is also used in other commands
such that it will be easier in the future to make other commands aware
of submodule.

This also solves d/f conflicts in case you replace a file/directory
with a submodule or vice versa.

The patches are still a bit rough, but the overall series seems
promising enough to me that I want to put it out here.

Any review, specifically on the design level welcome!

Thanks,
Stefan


Stefan Beller (14):
  lib-submodule-update.sh: reorder create_lib_submodule_repo
  lib-submodule-update.sh: define tests for recursing into submodules
  make is_submodule_populated gently
  connect_work_tree_and_git_dir: safely create leading directories
  update submodules: add submodule config parsing
  update submodules: add a config option to determine if submodules are
    updated
  update submodules: introduce is_interesting_submodule
  update submodules: move up prepare_submodule_repo_env
  update submodules: add submodule_go_from_to
  unpack-trees: pass old oid to verify_clean_submodule
  unpack-trees: check if we can perform the operation for submodules
  read-cache: remove_marked_cache_entries to wipe selected submodules.
  entry.c: update submodules when interesting
  builtin/checkout: add --recurse-submodules switch
diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt
index fa1d557e5b..ed9d63ef4a 100644
--- a/Documentation/git-read-tree.txt
+++ b/Documentation/git-read-tree.txt
@@ -115,6 +115,12 @@ OPTIONS
 	directories the index file and index output file are
 	located in.
 
+--[no-]recurse-submodules::
+	Using --recurse-submodules will update the content of all initialized
+	submodules according to the commit recorded in the superproject by
+	calling read-tree recursively, also setting the submodules HEAD to be
+	detached at that commit.
+
 --no-sparse-checkout::
 	Disable sparse checkout support even if `core.sparseCheckout`
 	is true.
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 207ce09771..e9c5fcfaf8 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -29,8 +29,8 @@ static const char * const checkout_usage[] = {
 	NULL,
 };
 
-int option_parse_recurse_submodules(const struct option *opt,
-				    const char *arg, int unset)
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
 {
 	if (unset) {
 		recurse_submodules = RECURSE_SUBMODULES_OFF;
diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 8ba64bc785..2dc5cc06da 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -15,10 +15,13 @@
 #include "builtin.h"
 #include "parse-options.h"
 #include "resolve-undo.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 static int nr_trees;
 static int read_empty;
 static struct tree *trees[MAX_UNPACK_TREES];
+int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 
 static int list_tree(unsigned char *sha1)
 {
@@ -96,6 +99,23 @@ static int debug_merge(const struct cache_entry * const *stages,
 	return 0;
 }
 
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
+{
+	if (unset) {
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
 static struct lock_file lock_file;
 
 int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
@@ -137,6 +157,9 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 			 N_("skip applying sparse checkout filter")),
 		OPT_BOOL(0, "debug-unpack", &opts.debug_unpack,
 			 N_("debug unpack-trees")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules },
 		OPT_END()
 	};
 
@@ -152,6 +175,12 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 
 	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
 
+	if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT) {
+		gitmodules_config();
+		git_config(submodule_config, NULL);
+		set_config_update_recurse_submodules(RECURSE_SUBMODULES_ON);
+	}
+
 	prefix_set = opts.prefix ? 1 : 0;
 	if (1 < opts.merge + opts.reset + prefix_set)
 		die("Which one? -m, --reset, or --prefix?");
diff --git a/submodule.c b/submodule.c
index a2cf8c9376..bc5fecf8c5 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1257,7 +1257,7 @@ static int submodule_has_dirty_index(const struct submodule *sub)
 	return finish_command(&cp);
 }
 
-void submodule_reset_index(const char *path)
+static void submodule_reset_index(const char *path)
 {
 	struct child_process cp = CHILD_PROCESS_INIT;
 	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 54cd8a6366..429cd1041d 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -4,7 +4,7 @@
 # - New submodule (no_submodule => add_sub1)
 # - Removed submodule (add_sub1 => remove_sub1)
 # - Updated submodule (add_sub1 => modify_sub1)
-# - Updated submodule recursively (modify_sub1 => modify_sub1_recursively)
+# - Updated submodule recursively (add_nested_sub => modify_sub1_recursively)
 # - Submodule updated to invalid commit (add_sub1 => invalid_sub1)
 # - Submodule updated from invalid commit (invalid_sub1 => valid_sub1)
 # - Submodule replaced by tracked files in directory (add_sub1 =>
@@ -20,8 +20,8 @@
 #                    /    ^
 #                   /     remove_sub1
 #                  /
-#       add_sub1  /-------O---------O
-#             |  /        ^         modify_sub1_recursive
+#       add_sub1  /-------O---------O--------O  modify_sub1_recursively
+#             |  /        ^         add_nested_sub
 #             | /         modify_sub1
 #             v/
 #      O------O-----------O---------O
@@ -96,12 +96,24 @@ create_lib_submodule_repo () {
 		git add sub1 &&
 		git commit -m "Modify sub1" &&
 
-		git checkout -b modify_sub1_recursively modify_sub1 &&
+		git checkout -b add_nested_sub modify_sub1 &&
 		git -C sub1 checkout -b "add_nested_sub" &&
 		git -C sub1 submodule add --branch no_submodule ../submodule_update_sub2 sub2 &&
 		git -C sub1 commit -a -m "add a nested submodule" &&
 		git add sub1 &&
 		git commit -a -m "update submodule, that updates a nested submodule" &&
+		git checkout -b modify_sub1_recursively &&
+		git -C sub1 checkout -b modify_sub1_recursively &&
+		git -C sub1/sub2 checkout -b modify_sub1_recursively &&
+		echo change >sub1/sub2/file3 &&
+		git -C sub1/sub2 add file3 &&
+		git -C sub1/sub2 commit -m "make a change in nested sub" &&
+		git -C sub1 add sub2 &&
+		git -C sub1 commit -m "update nested sub" &&
+		git add sub1 &&
+		git commit -m "update sub1, that updates nested sub" &&
+		git -C sub1 push origin modify_sub1_recursively &&
+		git -C sub1/sub2 push origin modify_sub1_recursively &&
 		git -C sub1 submodule deinit -f --all &&
 
 		git checkout -b replace_sub1_with_directory add_sub1 &&
@@ -200,9 +212,9 @@ reset_work_tree_to () {
 		git checkout -f "$1" &&
 		git status -u -s >actual &&
 		test_must_be_empty actual &&
-		sha1=$(git rev-parse --revs-only HEAD:sub1) &&
-		if test -n "$sha1" &&
-		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$sha1^{commit}")
+		hash=$(git rev-parse --revs-only HEAD:sub1) &&
+		if test -n "$hash" &&
+		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$hash^{commit}")
 		then
 			git submodule update --init --recursive "sub1"
 		fi
@@ -211,14 +223,23 @@ reset_work_tree_to () {
 
 reset_work_tree_to_interested () {
 	reset_work_tree_to $1 &&
-	# indicate we are interested in the submodule:
-	git -C submodule_update config submodule.sub1.url "bogus" &&
-	# also have it available:
+	# make the submodule git dirs available
 	if ! test -d submodule_update/.git/modules/sub1
 	then
 		mkdir -p submodule_update/.git/modules &&
 		cp -r submodule_update_repo/.git/modules/sub1 submodule_update/.git/modules/sub1
-	fi
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1 config --unset core.worktree
+	fi &&
+	if ! test -d submodule_update/.git/modules/sub1/modules/sub2
+	then
+		mkdir -p submodule_update/.git/modules/sub1/modules &&
+		cp -r submodule_update_repo/.git/modules/sub1/modules/sub2 submodule_update/.git/modules/sub1/modules/sub2
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1/modules/sub2 config --unset core.worktree
+	fi &&
+	# indicate we are interested in the submodule:
+	git -C submodule_update config submodule.sub1.url "bogus" &&
+	# sub1 might not be checked out, so use the git dir
+	git -C submodule_update/.git/modules/sub1 config submodule.sub2.url "bogus"
 }
 
 # Test that the superproject contains the content according to commit "$1"
@@ -234,6 +255,11 @@ test_superproject_content () {
 # Test that the given submodule at path "$1" contains the content according
 # to the submodule commit recorded in the superproject's commit "$2"
 test_submodule_content () {
+	if test "$1" == "-C"
+	then
+		cd "$2"
+		shift; shift;
+	fi
 	if test $# != 2
 	then
 		echo "test_submodule_content needs two arguments"
@@ -761,6 +787,11 @@ test_submodule_switch_recursing () {
 	then
 		RESULT=failure
 	fi
+
+	if test "$KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED" = 1
+	then
+		RESULT1=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -801,7 +832,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... but an ignored file is fine.
-	test_expect_success "$command: added submodule removes an untracked ignored file" '
+	test_expect_$RESULT1 "$command: added submodule removes an untracked ignored file" '
 		test_when_finished "rm submodule_update/.git/info/exclude" &&
 		prolog &&
 		reset_work_tree_to_interested no_submodule &&
@@ -966,21 +997,17 @@ test_submodule_switch_recursing () {
 		)
 	'
 
-	# This test fails, due to missing setup, we do not clone sub2 into
-	# submodule_update, because it doesn't exist in the 'add_sub1' version
-	#
-	test_expect_success "$command: modified submodule updates submodule recursively" '
+	# recursing deeper than one level doesn't work yet.
+	test_expect_failure "$command: modified submodule updates submodule recursively" '
 		prolog &&
-		reset_work_tree_to_interested add_sub1 &&
+		reset_work_tree_to_interested add_nested_sub &&
 		(
 			cd submodule_update &&
 			git branch -t modify_sub1_recursively origin/modify_sub1_recursively &&
-			test_must_fail $command modify_sub1_recursively &&
-			test_superproject_content origin/add_sub1 &&
-			test_submodule_content sub1 origin/add_sub1
-			# test_superproject_content origin/modify_sub1_recursively &&
-			# test_submodule_content sub1 origin/modify_sub1_recursively &&
-			# test_submodule_content sub1/sub2 no_submodule
+			$command modify_sub1_recursively &&
+			test_superproject_content origin/modify_sub1_recursively &&
+			test_submodule_content sub1 origin/modify_sub1_recursively &&
+			test_submodule_content -C sub1 sub2 origin/modify_sub1_recursively
 		)
 	'
 }
diff --git a/t/t1013-read-tree-submodule.sh b/t/t1013-read-tree-submodule.sh
index 20526aed34..7019d0a04f 100755
--- a/t/t1013-read-tree-submodule.sh
+++ b/t/t1013-read-tree-submodule.sh
@@ -5,6 +5,13 @@ test_description='read-tree can handle submodules'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-submodule-update.sh
 
+KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED=1
+
+test_submodule_switch_recursing "git read-tree --recurse-submodules -u -m"
+
+test_submodule_forced_switch_recursing "git read-tree --recurse-submodules -u --reset"
+
 test_submodule_switch "git read-tree -u -m"
 
 test_submodule_forced_switch "git read-tree -u --reset"

[PATCH 01/18] lib-submodule-update.sh: reorder create_lib_submodule_repo

[Stefan Beller]

Redraw the ASCII art describing the setup using more space, such that
it is easier to understand.  The leaf commits are now ordered the same
way the actual code is ordered.

Add empty lines to the setup code separating each of the leaf commits,
each starting with a "checkout -b".

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 49 ++++++++++++++++++++++++++++-------------------
 1 file changed, 29 insertions(+), 20 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 915eb4a7c6..5df528ea81 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -15,22 +15,27 @@
 # - Tracked file replaced by submodule (replace_sub1_with_file =>
 #   replace_file_with_sub1)
 #
-#                   --O-----O
-#                  /  ^     replace_directory_with_sub1
-#                 /   replace_sub1_with_directory
-#                /----O
-#               /     ^
-#              /      modify_sub1
-#      O------O-------O
-#      ^      ^\      ^
-#      |      | \     remove_sub1
-#      |      |  -----O-----O
-#      |      |   \   ^     replace_file_with_sub1
-#      |      |    \  replace_sub1_with_file
-#      |   add_sub1 --O-----O
-# no_submodule        ^     valid_sub1
-#                     invalid_sub1
+#                     ----O
+#                    /    ^
+#                   /     remove_sub1
+#                  /
+#       add_sub1  /-------O
+#             |  /        ^
+#             | /         modify_sub1
+#             v/
+#      O------O-----------O---------O
+#      ^       \          ^         replace_directory_with_sub1
+#      |        \         replace_sub1_with_directory
+# no_submodule   \
+#                 --------O---------O
+#                  \      ^         replace_file_with_sub1
+#                   \     replace_sub1_with_file
+#                    \
+#                     ----O---------O
+#                         ^         valid_sub1
+#                         invalid_sub1
 #
+
 create_lib_submodule_repo () {
 	git init submodule_update_repo &&
 	(
@@ -49,10 +54,11 @@ create_lib_submodule_repo () {
 		git config submodule.sub1.ignore all &&
 		git add .gitmodules &&
 		git commit -m "Add sub1" &&
-		git checkout -b remove_sub1 &&
+
+		git checkout -b remove_sub1 add_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "modify_sub1" "add_sub1" &&
+		git checkout -b modify_sub1 add_sub1 &&
 		git submodule update &&
 		(
 			cd sub1 &&
@@ -67,7 +73,7 @@ create_lib_submodule_repo () {
 		git add sub1 &&
 		git commit -m "Modify sub1" &&
 
-		git checkout -b "replace_sub1_with_directory" "add_sub1" &&
+		git checkout -b replace_sub1_with_directory add_sub1 &&
 		git submodule update &&
 		git -C sub1 checkout modifications &&
 		git rm --cached sub1 &&
@@ -75,22 +81,25 @@ create_lib_submodule_repo () {
 		git config -f .gitmodules --remove-section "submodule.sub1" &&
 		git add .gitmodules sub1/* &&
 		git commit -m "Replace sub1 with directory" &&
+
 		git checkout -b replace_directory_with_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "replace_sub1_with_file" "add_sub1" &&
+		git checkout -b replace_sub1_with_file add_sub1 &&
 		git rm sub1 &&
 		echo "content" >sub1 &&
 		git add sub1 &&
 		git commit -m "Replace sub1 with file" &&
+
 		git checkout -b replace_file_with_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "invalid_sub1" "add_sub1" &&
+		git checkout -b invalid_sub1 add_sub1 &&
 		git update-index --cacheinfo 160000 0123456789012345678901234567890123456789 sub1 &&
 		git commit -m "Invalid sub1 commit" &&
 		git checkout -b valid_sub1 &&
 		git revert HEAD &&
+
 		git checkout master
 	)
 }
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 02/18] lib-submodule-update.sh: do not use ./. as submodule remote

[Stefan Beller]

Adding the repository itself as a submodule does not make sense in the
real world. In our test suite we used to do that out of convenience in
some tests as the current repository has easiest access for setting up
'just a submodule'.

However this doesn't quite test the real world, so let's do not follow
this pattern any further and actually create an independent repository
that we can use as a submodule.

When using './.' as the remote the superproject and submodule share the
same objects, such that testing if a given sha1 is a valid commit works
in either repository.  As running commands in an unpopulated submodule
fall back to the superproject, this happens in `reset_work_tree_to`
to determine if we need to populate the submodule. Fix this bug by
checking in the actual remote now.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 5df528ea81..c0d6325133 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -37,6 +37,17 @@
 #
 
 create_lib_submodule_repo () {
+	git init submodule_update_sub1 &&
+	(
+		cd submodule_update_sub1 &&
+		echo "expect" >>.gitignore &&
+		echo "actual" >>.gitignore &&
+		echo "x" >file1 &&
+		echo "y" >file2 &&
+		git add .gitignore file1 file2 &&
+		git commit -m "Base inside first submodule" &&
+		git branch "no_submodule"
+	) &&
 	git init submodule_update_repo &&
 	(
 		cd submodule_update_repo &&
@@ -49,7 +60,7 @@ create_lib_submodule_repo () {
 		git branch "no_submodule" &&
 
 		git checkout -b "add_sub1" &&
-		git submodule add ./. sub1 &&
+		git submodule add ../submodule_update_sub1 sub1 &&
 		git config -f .gitmodules submodule.sub1.ignore all &&
 		git config submodule.sub1.ignore all &&
 		git add .gitmodules &&
@@ -162,7 +173,7 @@ reset_work_tree_to () {
 		test_must_be_empty actual &&
 		sha1=$(git rev-parse --revs-only HEAD:sub1) &&
 		if test -n "$sha1" &&
-		   test $(cd "sub1" && git rev-parse --verify "$sha1^{commit}")
+		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$sha1^{commit}")
 		then
 			git submodule update --init --recursive "sub1"
 		fi
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 03/18] lib-submodule-update: teach test_submodule_content the -C <dir> flag

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index c0d6325133..a906c92cfb 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -193,6 +193,11 @@ test_superproject_content () {
 # Test that the given submodule at path "$1" contains the content according
 # to the submodule commit recorded in the superproject's commit "$2"
 test_submodule_content () {
+	if test "$1" == "-C"
+	then
+		cd "$2"
+		shift; shift;
+	fi
 	if test $# != 2
 	then
 		echo "test_submodule_content needs two arguments"
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 04/18] lib-submodule-update.sh: replace sha1 by hash

[Stefan Beller]

Cleaning up code by generalising it.
Currently the mailing list discusses yet again how
to migrate away from sha1.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index a906c92cfb..83202c54fc 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -171,9 +171,9 @@ reset_work_tree_to () {
 		git checkout -f "$1" &&
 		git status -u -s >actual &&
 		test_must_be_empty actual &&
-		sha1=$(git rev-parse --revs-only HEAD:sub1) &&
-		if test -n "$sha1" &&
-		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$sha1^{commit}")
+		hash=$(git rev-parse --revs-only HEAD:sub1) &&
+		if test -n "$hash" &&
+		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$hash^{commit}")
 		then
 			git submodule update --init --recursive "sub1"
 		fi
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 05/18] lib-submodule-update.sh: define tests for recursing into submodules

[Stefan Beller]

Currently lib-submodule-update.sh provides 2 functions
test_submodule_switch and test_submodule_forced_switch that are used by a
variety of tests to ensure that submodules behave as expected. The current
expected behavior is that submodules are not touched at all (see
42639d2317a for the exact setup).

In the future we want to teach all these commands to recurse
into submodules. To do that, we'll add two testing functions to
submodule-update-lib.sh: test_submodule_switch_recursing and
test_submodule_forced_switch_recursing.

These two functions behave in analogy to the already existing functions
just with a different expectation on submodule behavior. The submodule
in the working tree is expected to be updated to the recorded submodule
version. The behavior is analogous to e.g. the behavior of files in a
nested directory in the working tree, where a change to the working tree
handles any arising directory/file conflicts just fine.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 506 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 504 insertions(+), 2 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 83202c54fc..aa196d4d42 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -4,6 +4,7 @@
 # - New submodule (no_submodule => add_sub1)
 # - Removed submodule (add_sub1 => remove_sub1)
 # - Updated submodule (add_sub1 => modify_sub1)
+# - Updated submodule recursively (add_nested_sub => modify_sub1_recursively)
 # - Submodule updated to invalid commit (add_sub1 => invalid_sub1)
 # - Submodule updated from invalid commit (invalid_sub1 => valid_sub1)
 # - Submodule replaced by tracked files in directory (add_sub1 =>
@@ -19,8 +20,8 @@
 #                    /    ^
 #                   /     remove_sub1
 #                  /
-#       add_sub1  /-------O
-#             |  /        ^
+#       add_sub1  /-------O---------O--------O  modify_sub1_recursively
+#             |  /        ^         add_nested_sub
 #             | /         modify_sub1
 #             v/
 #      O------O-----------O---------O
@@ -48,6 +49,17 @@ create_lib_submodule_repo () {
 		git commit -m "Base inside first submodule" &&
 		git branch "no_submodule"
 	) &&
+	git init submodule_update_sub2 &&
+	(
+		cd submodule_update_sub2
+		echo "expect" >>.gitignore &&
+		echo "actual" >>.gitignore &&
+		echo "x" >file1 &&
+		echo "y" >file2 &&
+		git add .gitignore file1 file2 &&
+		git commit -m "nested submodule base" &&
+		git branch "no_submodule"
+	) &&
 	git init submodule_update_repo &&
 	(
 		cd submodule_update_repo &&
@@ -84,6 +96,26 @@ create_lib_submodule_repo () {
 		git add sub1 &&
 		git commit -m "Modify sub1" &&
 
+		git checkout -b add_nested_sub modify_sub1 &&
+		git -C sub1 checkout -b "add_nested_sub" &&
+		git -C sub1 submodule add --branch no_submodule ../submodule_update_sub2 sub2 &&
+		git -C sub1 commit -a -m "add a nested submodule" &&
+		git add sub1 &&
+		git commit -a -m "update submodule, that updates a nested submodule" &&
+		git checkout -b modify_sub1_recursively &&
+		git -C sub1 checkout -b modify_sub1_recursively &&
+		git -C sub1/sub2 checkout -b modify_sub1_recursively &&
+		echo change >sub1/sub2/file3 &&
+		git -C sub1/sub2 add file3 &&
+		git -C sub1/sub2 commit -m "make a change in nested sub" &&
+		git -C sub1 add sub2 &&
+		git -C sub1 commit -m "update nested sub" &&
+		git add sub1 &&
+		git commit -m "update sub1, that updates nested sub" &&
+		git -C sub1 push origin modify_sub1_recursively &&
+		git -C sub1/sub2 push origin modify_sub1_recursively &&
+		git -C sub1 submodule deinit -f --all &&
+
 		git checkout -b replace_sub1_with_directory add_sub1 &&
 		git submodule update &&
 		git -C sub1 checkout modifications &&
@@ -150,6 +182,15 @@ test_git_directory_is_unchanged () {
 	)
 }
 
+test_git_directory_exists() {
+	test -e ".git/modules/$1" &&
+	if test -f sub1/.git
+	then
+		# does core.worktree point at the right place?
+		test "$(git -C .git/modules/$1 config core.worktree)" = "../../../$1"
+	fi
+}
+
 # Helper function to be executed at the start of every test below, it sets up
 # the submodule repo if it doesn't exist and configures the most problematic
 # settings for diff.ignoreSubmodules.
@@ -180,6 +221,27 @@ reset_work_tree_to () {
 	)
 }
 
+reset_work_tree_to_interested () {
+	reset_work_tree_to $1 &&
+	# make the submodule git dirs available
+	if ! test -d submodule_update/.git/modules/sub1
+	then
+		mkdir -p submodule_update/.git/modules &&
+		cp -r submodule_update_repo/.git/modules/sub1 submodule_update/.git/modules/sub1
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1 config --unset core.worktree
+	fi &&
+	if ! test -d submodule_update/.git/modules/sub1/modules/sub2
+	then
+		mkdir -p submodule_update/.git/modules/sub1/modules &&
+		cp -r submodule_update_repo/.git/modules/sub1/modules/sub2 submodule_update/.git/modules/sub1/modules/sub2
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1/modules/sub2 config --unset core.worktree
+	fi &&
+	# indicate we are interested in the submodule:
+	git -C submodule_update config submodule.sub1.url "bogus" &&
+	# sub1 might not be checked out, so use the git dir
+	git -C submodule_update/.git/modules/sub1 config submodule.sub2.url "bogus"
+}
+
 # Test that the superproject contains the content according to commit "$1"
 # (the work tree must match the index for everything but submodules but the
 # index must exactly match the given commit including any submodule SHA-1s).
@@ -700,3 +762,443 @@ test_submodule_forced_switch () {
 		)
 	'
 }
+
+# Test that submodule contents are correctly updated when switching
+# between commits that change a submodule.
+# Test that the following transitions are correctly handled:
+# (These tests are also above in the case where we expect no change
+#  in the submodule)
+# - Updated submodule
+# - New submodule
+# - Removed submodule
+# - Directory containing tracked files replaced by submodule
+# - Submodule replaced by tracked files in directory
+# - Submodule replaced by tracked file with the same name
+# - tracked file replaced by submodule
+#
+# New test cases
+# - Removing a submodule with a git directory absorbs the submodules
+#   git directory first into the superproject.
+
+test_submodule_switch_recursing () {
+	command="$1"
+	######################### Appearing submodule #########################
+	# Switching to a commit letting a submodule appear checks it out ...
+	test_expect_success "$command: added submodule is checked out" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... ignoring an empty existing directory ...
+	test_expect_success "$command: added submodule is checked out in empty dir" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			mkdir sub1 &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... unless there is an untracked file in its place.
+	test_expect_success "$command: added submodule doesn't remove untracked file with same name" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			: >sub1 &&
+			test_must_fail $command add_sub1 &&
+			test_superproject_content origin/no_submodule &&
+			test_must_be_empty sub1
+		)
+	'
+	# ... but an ignored file is fine.
+	test_expect_success "$command: added submodule removes an untracked ignored file" '
+		test_when_finished "rm submodule_update/.git/info/exclude" &&
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			: >sub1 &&
+			echo sub1 >.git/info/exclude
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Replacing a tracked file with a submodule produces a checked out submodule
+	test_expect_success "$command: replace tracked file with submodule checks out submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_file &&
+		(
+			cd submodule_update &&
+			git branch -t replace_file_with_sub1 origin/replace_file_with_sub1 &&
+			$command replace_file_with_sub1 &&
+			test_superproject_content origin/replace_file_with_sub1 &&
+			test_submodule_content sub1 origin/replace_file_with_sub1
+		)
+	'
+	# ... as does removing a directory with tracked files with a submodule.
+	test_expect_success "$command: replace directory with submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_directory &&
+		(
+			cd submodule_update &&
+			git branch -t replace_directory_with_sub1 origin/replace_directory_with_sub1 &&
+			$command replace_directory_with_sub1 &&
+			test_superproject_content origin/replace_directory_with_sub1 &&
+			test_submodule_content sub1 origin/replace_directory_with_sub1
+		)
+	'
+
+	######################## Disappearing submodule #######################
+	# Removing a submodule removes its work tree ...
+	test_expect_success "$command: removed submodule removes submodules working tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1
+		)
+	'
+	# ... absorbing a .git directory along the way.
+	test_expect_success "$command: removed submodule absorbs submodules .git directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1 &&
+			test_git_directory_exists sub1
+		)
+	'
+	# Replacing a submodule with files in a directory must succeeds
+	# when the submodule is clean
+	test_expect_success "$command: replace submodule with a directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_submodule_content sub1 origin/replace_sub1_with_directory
+		)
+	'
+	# ... absorbing a .git directory.
+	test_expect_success "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_git_directory_exists sub1
+		)
+	'
+
+	# Replacing it with a file ...
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file &&
+			test -f sub1
+		)
+	'
+
+	# ... must check its local work tree for untracked files
+	test_expect_success "$command: replace submodule with a file must fail with untracked files" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/untrackedfile &&
+			test_must_fail $command replace_sub1_with_file &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+
+	# ... and ignored files are ignroed
+	test_expect_success "$command: replace submodule with a file works ignores ignored files in submodule" '
+		test_when_finished "rm submodule_update/.git/modules/sub1/info/exclude" &&
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/ignored &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file &&
+			test -f sub1
+		)
+	'
+
+	########################## Modified submodule #########################
+	# Updating a submodule sha1 updates the submodule's work tree
+	test_expect_success "$command: modified submodule updates submodule work tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1 origin/modify_sub1 &&
+			$command modify_sub1 &&
+			test_superproject_content origin/modify_sub1 &&
+			test_submodule_content sub1 origin/modify_sub1
+		)
+	'
+
+	# Updating a submodule to an invalid sha1 doesn't update the
+	# superproject nor the submodule's work tree.
+	test_expect_success "$command: updating to a missing submodule commit fails" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t invalid_sub1 origin/invalid_sub1 &&
+			test_must_fail $command invalid_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+
+	test_expect_success "$command: modified submodule updates submodule recursively" '
+		prolog &&
+		reset_work_tree_to_interested add_nested_sub &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1_recursively origin/modify_sub1_recursively &&
+			$command modify_sub1_recursively &&
+			test_superproject_content origin/modify_sub1_recursively &&
+			test_submodule_content sub1 origin/modify_sub1_recursively &&
+			test_submodule_content -C sub1 sub2 origin/modify_sub1_recursively
+		)
+	'
+}
+
+# Test that submodule contents are updated when switching between commits
+# that change a submodule, but throwing away local changes in
+# the superproject as well as the submodule is allowed.
+test_submodule_forced_switch_recursing () {
+	command="$1"
+	######################### Appearing submodule #########################
+	# Switching to a commit letting a submodule appear creates empty dir ...
+	test_expect_success "$command: added submodule is checked out" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... and doesn't care if it already exists ...
+	test_expect_success "$command: added submodule ignores empty directory" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			mkdir sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... not caring about an untracked file either
+	test_expect_success "$command: added submodule does remove untracked unignored file with same name when forced" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			>sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Replacing a tracked file with a submodule checks out the submodule
+	test_expect_success "$command: replace tracked file with submodule populates the submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_file &&
+		(
+			cd submodule_update &&
+			git branch -t replace_file_with_sub1 origin/replace_file_with_sub1 &&
+			$command replace_file_with_sub1 &&
+			test_superproject_content origin/replace_file_with_sub1 &&
+			test_submodule_content sub1 origin/replace_file_with_sub1
+		)
+	'
+	# ... as does removing a directory with tracked files with a
+	# submodule.
+	test_expect_success "$command: replace directory with submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_directory &&
+		(
+			cd submodule_update &&
+			git branch -t replace_directory_with_sub1 origin/replace_directory_with_sub1 &&
+			$command replace_directory_with_sub1 &&
+			test_superproject_content origin/replace_directory_with_sub1 &&
+			test_submodule_content sub1 origin/replace_directory_with_sub1
+		)
+	'
+
+	######################## Disappearing submodule #######################
+	# Removing a submodule doesn't remove its work tree ...
+	test_expect_success "$command: removed submodule leaves submodule directory and its contents in place" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1
+		)
+	'
+	# ... especially when it contains a .git directory.
+	test_expect_success "$command: removed submodule leaves submodule containing a .git directory alone" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules/sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			test_git_directory_exists sub1 &&
+			! test -e sub1
+		)
+	'
+	# Replacing a submodule with files in a directory ...
+	test_expect_success "$command: replace submodule with a directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			test_must_fail $command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory
+		)
+	'
+	# ... absorbing a .git directory.
+	test_expect_success "$command: replace submodule containing a .git directory with a directory must fail" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules/sub1 &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_submodule_content sub1 origin/modify_sub1
+			test_git_directory_exists sub1
+		)
+	'
+	# Replacing it with a file
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file
+		)
+	'
+
+	# ... even if the submodule contains ignored files
+	test_expect_success "$command: replace submodule with a file ignoring ignored files" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/expect &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file
+		)
+	'
+
+	# ... but stops for untracked files that would be lost
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/untracked_file &&
+			test_must_fail $command replace_sub1_with_file &&
+			test_superproject_content origin/add_sub1 &&
+			test -f sub1/untracked_file
+		)
+	'
+
+	########################## Modified submodule #########################
+	# Updating a submodule sha1 updates the submodule's work tree
+	test_expect_success "$command: modified submodule updates submodule work tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1 origin/modify_sub1 &&
+			$command modify_sub1 &&
+			test_superproject_content origin/modify_sub1 &&
+			test_submodule_content sub1 origin/modify_sub1
+		)
+	'
+	# Updating a submodule to an invalid sha1 doesn't update the
+	# submodule's work tree, subsequent update will fail
+	test_expect_success "$command: modified submodule does not update submodule work tree to invalid commit" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t invalid_sub1 origin/invalid_sub1 &&
+			test_must_fail $command invalid_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Updating a submodule from an invalid sha1 updates
+	test_expect_success "$command: modified submodule does not update submodule work tree from invalid commit" '
+		prolog &&
+		reset_work_tree_to_interested invalid_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t valid_sub1 origin/valid_sub1 &&
+			test_must_fail $command valid_sub1 &&
+			test_superproject_content origin/invalid_sub1
+		)
+	'
+}
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 06/18] make is_submodule_populated gently

[Stefan Beller]

We need the gentle version in a later patch. As we have just one caller,
migrate the caller.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/grep.c | 2 +-
 submodule.c    | 7 ++-----
 submodule.h    | 8 +++++++-
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/builtin/grep.c b/builtin/grep.c
index 2c727ef499..b17835aed6 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -616,7 +616,7 @@ static int grep_submodule(struct grep_opt *opt, const unsigned char *sha1,
 {
 	if (!is_submodule_initialized(path))
 		return 0;
-	if (!is_submodule_populated(path)) {
+	if (!is_submodule_populated_gently(path, NULL)) {
 		/*
 		 * If searching history, check for the presense of the
 		 * submodule's gitdir before skipping the submodule.
diff --git a/submodule.c b/submodule.c
index 3b98766a6b..0e55372f37 100644
--- a/submodule.c
+++ b/submodule.c
@@ -234,15 +234,12 @@ int is_submodule_initialized(const char *path)
 	return ret;
 }
 
-/*
- * Determine if a submodule has been populated at a given 'path'
- */
-int is_submodule_populated(const char *path)
+int is_submodule_populated_gently(const char *path, int *return_error_code)
 {
 	int ret = 0;
 	char *gitdir = xstrfmt("%s/.git", path);
 
-	if (resolve_gitdir(gitdir))
+	if (resolve_gitdir_gently(gitdir, return_error_code))
 		ret = 1;
 
 	free(gitdir);
diff --git a/submodule.h b/submodule.h
index 05ab674f06..0b915bd3ac 100644
--- a/submodule.h
+++ b/submodule.h
@@ -41,7 +41,13 @@ extern int submodule_config(const char *var, const char *value, void *cb);
 extern void gitmodules_config(void);
 extern void gitmodules_config_sha1(const unsigned char *commit_sha1);
 extern int is_submodule_initialized(const char *path);
-extern int is_submodule_populated(const char *path);
+/*
+ * Determine if a submodule has been populated at a given 'path' by checking if
+ * the <path>/.git resolves to a valid git repository.
+ * If return_error_code is NULL, die on error.
+ * Otherwise the return error code is the same as of resolve_gitdir_gently.
+ */
+extern int is_submodule_populated_gently(const char *path, int *return_error_code);
 extern int parse_submodule_update_strategy(const char *value,
 		struct submodule_update_strategy *dst);
 extern const char *submodule_strategy_to_string(const struct submodule_update_strategy *s);
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 07/18] connect_work_tree_and_git_dir: safely create leading directories

[Stefan Beller]

In a later patch we'll use connect_work_tree_and_git_dir when the
directory for the gitlink file doesn't exist yet. This patch makes
connect_work_tree_and_git_dir safe to use for both cases of
either the git dir or the working dir missing.

To do so, we need to call safe_create_leading_directories[_const]
on both directories. However this has to happen before we construct
the absolute paths as real_pathdup assumes the directories to
be there already.

So for both the config file in the git dir as well as the .git link
file we need to
a) construct the name
b) call SCLD
c) get the absolute path
d) once a-c is done for both we can consume the absolute path
   to compute the relative path to each other and store those
   relative paths.

The implementation provided here puts a) and b) for both cases first,
and then performs c and d after.

One of the two users of 'connect_work_tree_and_git_dir' already checked
for the directory being there, so we can loose that check as
connect_work_tree_and_git_dir handles this functionality now.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 dir.c       | 32 +++++++++++++++++++++-----------
 submodule.c | 11 ++---------
 2 files changed, 23 insertions(+), 20 deletions(-)

diff --git a/dir.c b/dir.c
index 4541f9e146..6f52af7abb 100644
--- a/dir.c
+++ b/dir.c
@@ -2728,23 +2728,33 @@ void untracked_cache_add_to_index(struct index_state *istate,
 /* Update gitfile and core.worktree setting to connect work tree and git dir */
 void connect_work_tree_and_git_dir(const char *work_tree_, const char *git_dir_)
 {
-	struct strbuf file_name = STRBUF_INIT;
+	struct strbuf gitfile_sb = STRBUF_INIT;
+	struct strbuf cfg_sb = STRBUF_INIT;
 	struct strbuf rel_path = STRBUF_INIT;
-	char *git_dir = real_pathdup(git_dir_);
-	char *work_tree = real_pathdup(work_tree_);
+	char *git_dir, *work_tree;
 
-	/* Update gitfile */
-	strbuf_addf(&file_name, "%s/.git", work_tree);
-	write_file(file_name.buf, "gitdir: %s",
-		   relative_path(git_dir, work_tree, &rel_path));
+	/* Prepare .git file */
+	strbuf_addf(&gitfile_sb, "%s/.git", work_tree_);
+	if (safe_create_leading_directories_const(gitfile_sb.buf))
+		die(_("could not create directories for %s"), gitfile_sb.buf);
+
+	/* Prepare config file */
+	strbuf_addf(&cfg_sb, "%s/config", git_dir_);
+	if (safe_create_leading_directories_const(cfg_sb.buf))
+		die(_("could not create directories for %s"), cfg_sb.buf);
 
+	git_dir = real_pathdup(git_dir_);
+	work_tree = real_pathdup(work_tree_);
+
+	/* Write .git file */
+	write_file(gitfile_sb.buf, "gitdir: %s",
+		   relative_path(git_dir, work_tree, &rel_path));
 	/* Update core.worktree setting */
-	strbuf_reset(&file_name);
-	strbuf_addf(&file_name, "%s/config", git_dir);
-	git_config_set_in_file(file_name.buf, "core.worktree",
+	git_config_set_in_file(cfg_sb.buf, "core.worktree",
 			       relative_path(work_tree, git_dir, &rel_path));
 
-	strbuf_release(&file_name);
+	strbuf_release(&gitfile_sb);
+	strbuf_release(&cfg_sb);
 	strbuf_release(&rel_path);
 	free(work_tree);
 	free(git_dir);
diff --git a/submodule.c b/submodule.c
index 0e55372f37..04d185738f 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1442,8 +1442,6 @@ void absorb_git_dir_into_superproject(const char *prefix,
 
 	/* Not populated? */
 	if (!sub_git_dir) {
-		char *real_new_git_dir;
-		const char *new_git_dir;
 		const struct submodule *sub;
 
 		if (err_code == READ_GITFILE_ERR_STAT_FAILED) {
@@ -1466,13 +1464,8 @@ void absorb_git_dir_into_superproject(const char *prefix,
 		sub = submodule_from_path(null_sha1, path);
 		if (!sub)
 			die(_("could not lookup name for submodule '%s'"), path);
-		new_git_dir = git_path("modules/%s", sub->name);
-		if (safe_create_leading_directories_const(new_git_dir) < 0)
-			die(_("could not create directory '%s'"), new_git_dir);
-		real_new_git_dir = real_pathdup(new_git_dir);
-		connect_work_tree_and_git_dir(path, real_new_git_dir);
-
-		free(real_new_git_dir);
+		connect_work_tree_and_git_dir(path,
+			git_path("modules/%s", sub->name));
 	} else {
 		/* Is it already absorbed into the superprojects git dir? */
 		char *real_sub_git_dir = real_pathdup(sub_git_dir);
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 08/18] update submodules: add submodule config parsing

[Stefan Beller]

Similar to b33a15b08 (push: add recurseSubmodules config option,
2015-11-17) and 027771fcb1 (submodule: allow erroneous values for the
fetchRecurseSubmodules option, 2015-08-17), we add submodule-config code
that is later used to parse whether we are interested in updating
submodules.

We need the `die_on_error` parameter to be able to call this parsing
function for the config file as well, which if incorrect lets Git die.

As we're just touching the header file, also mark all functions extern.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule-config.c | 20 ++++++++++++++++++++
 submodule-config.h | 17 +++++++++--------
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/submodule-config.c b/submodule-config.c
index 93453909cf..3e8e380d98 100644
--- a/submodule-config.c
+++ b/submodule-config.c
@@ -234,6 +234,26 @@ int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg)
 	return parse_fetch_recurse(opt, arg, 1);
 }
 
+static int parse_update_recurse(const char *opt, const char *arg,
+				int die_on_error)
+{
+	switch (git_config_maybe_bool(opt, arg)) {
+	case 1:
+		return RECURSE_SUBMODULES_ON;
+	case 0:
+		return RECURSE_SUBMODULES_OFF;
+	default:
+		if (die_on_error)
+			die("bad %s argument: %s", opt, arg);
+		return RECURSE_SUBMODULES_ERROR;
+	}
+}
+
+int parse_update_recurse_submodules_arg(const char *opt, const char *arg)
+{
+	return parse_update_recurse(opt, arg, 1);
+}
+
 static int parse_push_recurse(const char *opt, const char *arg,
 			       int die_on_error)
 {
diff --git a/submodule-config.h b/submodule-config.h
index 70f19363fd..d434ecdb45 100644
--- a/submodule-config.h
+++ b/submodule-config.h
@@ -22,16 +22,17 @@ struct submodule {
 	int recommend_shallow;
 };
 
-int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg);
-int parse_push_recurse_submodules_arg(const char *opt, const char *arg);
-int parse_submodule_config_option(const char *var, const char *value);
-const struct submodule *submodule_from_name(const unsigned char *commit_or_tree,
-		const char *name);
-const struct submodule *submodule_from_path(const unsigned char *commit_or_tree,
-		const char *path);
+extern int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_update_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_push_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_submodule_config_option(const char *var, const char *value);
+extern const struct submodule *submodule_from_name(
+		const unsigned char *commit_or_tree, const char *name);
+extern const struct submodule *submodule_from_path(
+		const unsigned char *commit_or_tree, const char *path);
 extern int gitmodule_sha1_from_commit(const unsigned char *commit_sha1,
 				      unsigned char *gitmodules_sha1,
 				      struct strbuf *rev);
-void submodule_free(void);
+extern void submodule_free(void);
 
 #endif /* SUBMODULE_CONFIG_H */
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 09/18] update submodules: add a config option to determine if submodules are updated

[Stefan Beller]

In later patches we introduce the options and flag for commands
that modify the working directory, e.g. git-checkout.

Have a central place to store such settings whether we want to update
a submodule.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 6 ++++++
 submodule.h | 1 +
 2 files changed, 7 insertions(+)

diff --git a/submodule.c b/submodule.c
index 04d185738f..591f4a694e 100644
--- a/submodule.c
+++ b/submodule.c
@@ -17,6 +17,7 @@
 #include "worktree.h"
 
 static int config_fetch_recurse_submodules = RECURSE_SUBMODULES_ON_DEMAND;
+static int config_update_recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 static int parallel_jobs = 1;
 static struct string_list changed_submodule_paths = STRING_LIST_INIT_NODUP;
 static int initialized_fetch_ref_tips;
@@ -542,6 +543,11 @@ void set_config_fetch_recurse_submodules(int value)
 	config_fetch_recurse_submodules = value;
 }
 
+void set_config_update_recurse_submodules(int value)
+{
+	config_update_recurse_submodules = value;
+}
+
 static int has_remote(const char *refname, const struct object_id *oid,
 		      int flags, void *cb_data)
 {
diff --git a/submodule.h b/submodule.h
index 0b915bd3ac..b4e60c08d2 100644
--- a/submodule.h
+++ b/submodule.h
@@ -64,6 +64,7 @@ extern void show_submodule_inline_diff(FILE *f, const char *path,
 		const char *del, const char *add, const char *reset,
 		const struct diff_options *opt);
 extern void set_config_fetch_recurse_submodules(int value);
+extern void set_config_update_recurse_submodules(int value);
 extern void check_for_new_submodule_commits(unsigned char new_sha1[20]);
 extern int fetch_populated_submodules(const struct argv_array *options,
 			       const char *prefix, int command_line_option,
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 10/18] submodules: introduce check to see whether to touch a submodule

[Stefan Beller]

In later patches we introduce the --recurse-submodule flag for commands
that modify the working directory, e.g. git-checkout.

It is potentially expensive to check if a submodule needs an update,
because a common theme to interact with submodules is to spawn a child
process for each interaction.

So let's introduce a function that checks if a submodule needs
to be checked for an update before attempting the update.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 16 ++++++++++++++++
 submodule.h |  7 +++++++
 2 files changed, 23 insertions(+)

diff --git a/submodule.c b/submodule.c
index 591f4a694e..8b2c0212be 100644
--- a/submodule.c
+++ b/submodule.c
@@ -548,6 +548,22 @@ void set_config_update_recurse_submodules(int value)
 	config_update_recurse_submodules = value;
 }
 
+int should_update_submodules(void)
+{
+	return config_update_recurse_submodules == RECURSE_SUBMODULES_ON;
+}
+
+const struct submodule *submodule_from_ce(const struct cache_entry *ce)
+{
+	if (!S_ISGITLINK(ce->ce_mode))
+		return NULL;
+
+	if (!should_update_submodules())
+		return NULL;
+
+	return submodule_from_path(null_sha1, ce->name);
+}
+
 static int has_remote(const char *refname, const struct object_id *oid,
 		      int flags, void *cb_data)
 {
diff --git a/submodule.h b/submodule.h
index b4e60c08d2..6f3fe85c7c 100644
--- a/submodule.h
+++ b/submodule.h
@@ -65,6 +65,13 @@ extern void show_submodule_inline_diff(FILE *f, const char *path,
 		const struct diff_options *opt);
 extern void set_config_fetch_recurse_submodules(int value);
 extern void set_config_update_recurse_submodules(int value);
+/* Check if we want to update any submodule.*/
+extern int should_update_submodules(void);
+/*
+ * Returns the submodule struct if the given ce entry is a submodule
+ * and it should be updated. Returns NULL otherwise.
+ */
+extern const struct submodule *submodule_from_ce(const struct cache_entry *ce);
 extern void check_for_new_submodule_commits(unsigned char new_sha1[20]);
 extern int fetch_populated_submodules(const struct argv_array *options,
 			       const char *prefix, int command_line_option,
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 11/18] update submodules: move up prepare_submodule_repo_env

[Stefan Beller]

In a later patch we need to prepare the submodule environment with
another git directory, so split up the function.

Also move it up in the file such that we do not need to declare the
function later before using it.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/submodule.c b/submodule.c
index 8b2c0212be..0b2596e88a 100644
--- a/submodule.c
+++ b/submodule.c
@@ -356,6 +356,23 @@ static void print_submodule_summary(struct rev_info *rev, FILE *f,
 	strbuf_release(&sb);
 }
 
+static void prepare_submodule_repo_env_no_git_dir(struct argv_array *out)
+{
+	const char * const *var;
+
+	for (var = local_repo_env; *var; var++) {
+		if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
+			argv_array_push(out, *var);
+	}
+}
+
+void prepare_submodule_repo_env(struct argv_array *out)
+{
+	prepare_submodule_repo_env_no_git_dir(out);
+	argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
+			 DEFAULT_GIT_DIR_ENVIRONMENT);
+}
+
 /* Helper function to display the submodule header line prior to the full
  * summary output. If it can locate the submodule objects directory it will
  * attempt to lookup both the left and right commits and put them into the
@@ -1390,18 +1407,6 @@ int parallel_submodules(void)
 	return parallel_jobs;
 }
 
-void prepare_submodule_repo_env(struct argv_array *out)
-{
-	const char * const *var;
-
-	for (var = local_repo_env; *var; var++) {
-		if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
-			argv_array_push(out, *var);
-	}
-	argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
-			 DEFAULT_GIT_DIR_ENVIRONMENT);
-}
-
 /*
  * Embeds a single submodules git directory into the superprojects git dir,
  * non recursively.
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 12/18] update submodules: add submodule_move_head

[Stefan Beller]

In later patches we introduce the options and flag for commands
that modify the working directory, e.g. git-checkout.

This piece of code will be used universally for
all these working tree modifications as it
* supports dry run to answer the question:
  "Is it safe to change the submodule to this new state?"
  e.g. is it overwriting untracked files or are there local
  changes that would be overwritten?
* supports a force flag that can be used for resetting
  the tree.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 submodule.h |   7 ++++
 2 files changed, 142 insertions(+)

diff --git a/submodule.c b/submodule.c
index 0b2596e88a..bc5fecf8c5 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1239,6 +1239,141 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
 	return ret;
 }
 
+static int submodule_has_dirty_index(const struct submodule *sub)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	argv_array_pushl(&cp.args, "diff-index", "--quiet", \
+					"--cached", "HEAD", NULL);
+	cp.no_stdin = 1;
+	cp.no_stdout = 1;
+	cp.dir = sub->path;
+	if (start_command(&cp))
+		die("could not recurse into submodule '%s'", sub->path);
+
+	return finish_command(&cp);
+}
+
+static void submodule_reset_index(const char *path)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.dir = path;
+
+	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
+	argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
+
+	argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);
+
+	if (run_command(&cp))
+		die("could not reset submodule index");
+}
+
+/**
+ * Moves a submodule at a given path from a given head to another new head.
+ * For edge cases (a submodule coming into existence or removing a submodule)
+ * pass NULL for old or new respectively.
+ */
+int submodule_move_head(const char *path,
+			 const char *old,
+			 const char *new,
+			 unsigned flags)
+{
+	int ret = 0;
+	struct child_process cp = CHILD_PROCESS_INIT;
+	const struct submodule *sub;
+
+	sub = submodule_from_path(null_sha1, path);
+
+	if (!sub)
+		die("BUG: could not get submodule information for '%s'", path);
+
+	if (old && !(flags & SUBMODULE_MOVE_HEAD_FORCE)) {
+		/* Check if the submodule has a dirty index. */
+		if (submodule_has_dirty_index(sub))
+			return error(_("submodule '%s' has dirty index"), path);
+	}
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
+		if (old) {
+			if (!submodule_uses_gitfile(path))
+				absorb_git_dir_into_superproject("", path,
+					ABSORB_GITDIR_RECURSE_SUBMODULES);
+		} else {
+			struct strbuf sb = STRBUF_INIT;
+			strbuf_addf(&sb, "%s/modules/%s",
+				    get_git_common_dir(), sub->name);
+			connect_work_tree_and_git_dir(path, sb.buf);
+			strbuf_release(&sb);
+
+			/* make sure the index is clean as well */
+			submodule_reset_index(path);
+		}
+	}
+
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.dir = path;
+
+	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
+	argv_array_pushl(&cp.args, "read-tree", NULL);
+
+	if (flags & SUBMODULE_MOVE_HEAD_DRY_RUN)
+		argv_array_push(&cp.args, "-n");
+	else
+		argv_array_push(&cp.args, "-u");
+
+	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
+		argv_array_push(&cp.args, "--reset");
+	else
+		argv_array_push(&cp.args, "-m");
+
+	argv_array_push(&cp.args, old ? old : EMPTY_TREE_SHA1_HEX);
+	argv_array_push(&cp.args, new ? new : EMPTY_TREE_SHA1_HEX);
+
+	if (run_command(&cp)) {
+		ret = -1;
+		goto out;
+	}
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
+		if (new) {
+			struct child_process cp1 = CHILD_PROCESS_INIT;
+			/* also set the HEAD accordingly */
+			cp1.git_cmd = 1;
+			cp1.no_stdin = 1;
+			cp1.dir = path;
+
+			argv_array_pushl(&cp1.args, "update-ref", "HEAD",
+					 new ? new : EMPTY_TREE_SHA1_HEX, NULL);
+
+			if (run_command(&cp1)) {
+				ret = -1;
+				goto out;
+			}
+		} else {
+			struct strbuf sb = STRBUF_INIT;
+
+			strbuf_addf(&sb, "%s/.git", path);
+			unlink_or_warn(sb.buf);
+			strbuf_release(&sb);
+
+			if (is_empty_dir(path))
+				rmdir_or_warn(path);
+		}
+	}
+out:
+	return ret;
+}
+
 static int find_first_merges(struct object_array *result, const char *path,
 		struct commit *a, struct commit *b)
 {
diff --git a/submodule.h b/submodule.h
index 6f3fe85c7c..4cdf6445f7 100644
--- a/submodule.h
+++ b/submodule.h
@@ -96,6 +96,13 @@ extern int push_unpushed_submodules(struct sha1_array *commits,
 extern void connect_work_tree_and_git_dir(const char *work_tree, const char *git_dir);
 extern int parallel_submodules(void);
 
+#define SUBMODULE_MOVE_HEAD_DRY_RUN (1<<0)
+#define SUBMODULE_MOVE_HEAD_FORCE   (1<<1)
+extern int submodule_move_head(const char *path,
+			       const char *old,
+			       const char *new,
+			       unsigned flags);
+
 /*
  * Prepare the "env_array" parameter of a "struct child_process" for executing
  * a submodule by clearing any repo-specific envirionment variables, but
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 13/18] unpack-trees: pass old oid to verify_clean_submodule

[Stefan Beller]

The check (which uses the old oid) is yet to be implemented, but this part
is just a refactor, so it can go separately first.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 unpack-trees.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 3a8ee19fe8..616a0ae4b2 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1407,7 +1407,8 @@ static void invalidate_ce_path(const struct cache_entry *ce,
  * Currently, git does not checkout subprojects during a superproject
  * checkout, so it is not going to overwrite anything.
  */
-static int verify_clean_submodule(const struct cache_entry *ce,
+static int verify_clean_submodule(const char *old_sha1,
+				  const struct cache_entry *ce,
 				  enum unpack_trees_error_types error_type,
 				  struct unpack_trees_options *o)
 {
@@ -1427,16 +1428,18 @@ static int verify_clean_subdirectory(const struct cache_entry *ce,
 	struct dir_struct d;
 	char *pathbuf;
 	int cnt = 0;
-	unsigned char sha1[20];
 
-	if (S_ISGITLINK(ce->ce_mode) &&
-	    resolve_gitlink_ref(ce->name, "HEAD", sha1) == 0) {
-		/* If we are not going to update the submodule, then
+	if (S_ISGITLINK(ce->ce_mode)) {
+		unsigned char sha1[20];
+		int sub_head = resolve_gitlink_ref(ce->name, "HEAD", sha1);
+		/*
+		 * If we are not going to update the submodule, then
 		 * we don't care.
 		 */
-		if (!hashcmp(sha1, ce->oid.hash))
+		if (!sub_head && !hashcmp(sha1, ce->oid.hash))
 			return 0;
-		return verify_clean_submodule(ce, error_type, o);
+		return verify_clean_submodule(sub_head ? NULL : sha1_to_hex(sha1),
+					      ce, error_type, o);
 	}
 
 	/*
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 14/18] unpack-trees: check if we can perform the operation for submodules

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 unpack-trees.c | 131 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
 unpack-trees.h |   1 +
 2 files changed, 123 insertions(+), 9 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 616a0ae4b2..8333da2cc9 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -10,6 +10,8 @@
 #include "attr.h"
 #include "split-index.h"
 #include "dir.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 /*
  * Error messages expected by scripts out of plumbing commands such as
@@ -45,6 +47,9 @@ static const char *unpack_plumbing_errors[NB_UNPACK_TREES_ERROR_TYPES] = {
 
 	/* ERROR_WOULD_LOSE_ORPHANED_REMOVED */
 	"Working tree file '%s' would be removed by sparse checkout update.",
+
+	/* ERROR_WOULD_LOSE_SUBMODULE */
+	"Submodule '%s' cannot checkout new HEAD.",
 };
 
 #define ERRORMSG(o,type) \
@@ -161,6 +166,8 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 		_("The following working tree files would be overwritten by sparse checkout update:\n%s");
 	msgs[ERROR_WOULD_LOSE_ORPHANED_REMOVED] =
 		_("The following working tree files would be removed by sparse checkout update:\n%s");
+	msgs[ERROR_WOULD_LOSE_SUBMODULE] =
+		_("Submodule '%s' cannot checkout new HEAD");
 
 	opts->show_all_errors = 1;
 	/* rejected paths may not have a static buffer */
@@ -240,12 +247,75 @@ static void display_error_msgs(struct unpack_trees_options *o)
 		fprintf(stderr, _("Aborting\n"));
 }
 
+static int check_submodule_move_head(const struct cache_entry *ce,
+				     const char *old_id,
+				     const char *new_id,
+				     struct unpack_trees_options *o)
+{
+	const struct submodule *sub = submodule_from_ce(ce);
+	if (!sub)
+		return 0;
+
+	switch (sub->update_strategy.type) {
+	case SM_UPDATE_UNSPECIFIED:
+	case SM_UPDATE_CHECKOUT:
+		if (submodule_move_head(ce->name, old_id, new_id, SUBMODULE_MOVE_HEAD_DRY_RUN))
+			return o->gently ? -1 :
+				add_rejected_path(o, ERROR_WOULD_LOSE_SUBMODULE, ce->name);
+		return 0;
+	case SM_UPDATE_NONE:
+		return 0;
+	case SM_UPDATE_REBASE:
+	case SM_UPDATE_MERGE:
+	case SM_UPDATE_COMMAND:
+	default:
+		warning(_("submodule update strategy not supported for submodule '%s'"), ce->name);
+		return -1;
+	}
+}
+
+static void reload_gitmodules_file(struct index_state *index,
+				   struct checkout *state)
+{
+	int i;
+	for (i = 0; i < index->cache_nr; i++) {
+		struct cache_entry *ce = index->cache[i];
+		if (ce->ce_flags & CE_UPDATE) {
+			int r = strcmp(ce->name, ".gitmodules");
+			if (r < 0)
+				continue;
+			else if (r == 0) {
+				submodule_free();
+				checkout_entry(ce, state, NULL);
+				gitmodules_config();
+				git_config(submodule_config, NULL);
+			} else
+				break;
+		}
+	}
+}
+
 /*
  * Unlink the last component and schedule the leading directories for
  * removal, such that empty directories get removed.
  */
 static void unlink_entry(const struct cache_entry *ce)
 {
+	const struct submodule *sub = submodule_from_ce(ce);
+	if (sub) {
+		switch (sub->update_strategy.type) {
+		case SM_UPDATE_UNSPECIFIED:
+		case SM_UPDATE_CHECKOUT:
+		case SM_UPDATE_REBASE:
+		case SM_UPDATE_MERGE:
+			submodule_move_head(ce->name, "HEAD", NULL,
+					    SUBMODULE_MOVE_HEAD_FORCE);
+			break;
+		case SM_UPDATE_NONE:
+		case SM_UPDATE_COMMAND:
+			return; /* Do not touch the submodule. */
+		}
+	}
 	if (!check_leading_path(ce->name, ce_namelen(ce)))
 		return;
 	if (remove_or_warn(ce->ce_mode, ce->name))
@@ -301,6 +371,9 @@ static int check_updates(struct unpack_trees_options *o)
 	remove_marked_cache_entries(index);
 	remove_scheduled_dirs();
 
+	if (should_update_submodules() && o->update && !o->dry_run)
+		reload_gitmodules_file(index, &state);
+
 	for (i = 0; i < index->cache_nr; i++) {
 		struct cache_entry *ce = index->cache[i];
 
@@ -1358,17 +1431,26 @@ static int verify_uptodate_1(const struct cache_entry *ce,
 	if (!lstat(ce->name, &st)) {
 		int flags = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE;
 		unsigned changed = ie_match_stat(o->src_index, ce, &st, flags);
+
+		if (submodule_from_ce(ce)) {
+			int r = check_submodule_move_head(ce,
+				"HEAD", oid_to_hex(&ce->oid), o);
+			if (r)
+				return o->gently ? -1 :
+					add_rejected_path(o, error_type, ce->name);
+			return 0;
+		}
+
 		if (!changed)
 			return 0;
 		/*
-		 * NEEDSWORK: the current default policy is to allow
-		 * submodule to be out of sync wrt the superproject
-		 * index.  This needs to be tightened later for
-		 * submodules that are marked to be automatically
-		 * checked out.
+		 * Historic default policy was to allow submodule to be out
+		 * of sync wrt the superproject index. If the submodule was
+		 * not considered interesting above, we don't care here.
 		 */
 		if (S_ISGITLINK(ce->ce_mode))
 			return 0;
+
 		errno = 0;
 	}
 	if (errno == ENOENT)
@@ -1412,7 +1494,11 @@ static int verify_clean_submodule(const char *old_sha1,
 				  enum unpack_trees_error_types error_type,
 				  struct unpack_trees_options *o)
 {
-	return 0;
+	if (!submodule_from_ce(ce))
+		return 0;
+
+	return check_submodule_move_head(ce, old_sha1,
+					 oid_to_hex(&ce->oid), o);
 }
 
 static int verify_clean_subdirectory(const struct cache_entry *ce,
@@ -1578,9 +1664,15 @@ static int verify_absent_1(const struct cache_entry *ce,
 		path = xmemdupz(ce->name, len);
 		if (lstat(path, &st))
 			ret = error_errno("cannot stat '%s'", path);
-		else
-			ret = check_ok_to_remove(path, len, DT_UNKNOWN, NULL,
-						 &st, error_type, o);
+		else {
+			if (submodule_from_ce(ce))
+				ret = check_submodule_move_head(ce,
+								oid_to_hex(&ce->oid),
+								NULL, o);
+			else
+				ret = check_ok_to_remove(path, len, DT_UNKNOWN, NULL,
+							 &st, error_type, o);
+		}
 		free(path);
 		return ret;
 	} else if (lstat(ce->name, &st)) {
@@ -1588,6 +1680,10 @@ static int verify_absent_1(const struct cache_entry *ce,
 			return error_errno("cannot stat '%s'", ce->name);
 		return 0;
 	} else {
+		if (submodule_from_ce(ce))
+			return check_submodule_move_head(ce, oid_to_hex(&ce->oid),
+							 NULL, o);
+
 		return check_ok_to_remove(ce->name, ce_namelen(ce),
 					  ce_to_dtype(ce), ce, &st,
 					  error_type, o);
@@ -1643,6 +1739,15 @@ static int merged_entry(const struct cache_entry *ce,
 			return -1;
 		}
 		invalidate_ce_path(merge, o);
+
+		if (submodule_from_ce(ce)) {
+			int ret = check_submodule_move_head(ce, NULL,
+							    oid_to_hex(&ce->oid),
+							    o);
+			if (ret)
+				return ret;
+		}
+
 	} else if (!(old->ce_flags & CE_CONFLICTED)) {
 		/*
 		 * See if we can re-use the old CE directly?
@@ -1663,6 +1768,14 @@ static int merged_entry(const struct cache_entry *ce,
 			update |= old->ce_flags & (CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
 			invalidate_ce_path(old, o);
 		}
+
+		if (submodule_from_ce(ce)) {
+			int ret = check_submodule_move_head(ce, oid_to_hex(&old->oid),
+							    oid_to_hex(&ce->oid),
+							    o);
+			if (ret)
+				return ret;
+		}
 	} else {
 		/*
 		 * Previously unmerged entry left as an existence
diff --git a/unpack-trees.h b/unpack-trees.h
index 36a73a6d00..6c48117b84 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -21,6 +21,7 @@ enum unpack_trees_error_types {
 	ERROR_SPARSE_NOT_UPTODATE_FILE,
 	ERROR_WOULD_LOSE_ORPHANED_OVERWRITTEN,
 	ERROR_WOULD_LOSE_ORPHANED_REMOVED,
+	ERROR_WOULD_LOSE_SUBMODULE,
 	NB_UNPACK_TREES_ERROR_TYPES
 };
 
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 15/18] read-cache, remove_marked_cache_entries: wipe selected submodules.

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 read-cache.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/read-cache.c b/read-cache.c
index 9054369dd0..9a2abacf7a 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -18,6 +18,8 @@
 #include "varint.h"
 #include "split-index.h"
 #include "utf8.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -520,6 +522,22 @@ int remove_index_entry_at(struct index_state *istate, int pos)
 	return 1;
 }
 
+static void remove_submodule_according_to_strategy(const struct submodule *sub)
+{
+	switch (sub->update_strategy.type) {
+	case SM_UPDATE_UNSPECIFIED:
+	case SM_UPDATE_CHECKOUT:
+	case SM_UPDATE_REBASE:
+	case SM_UPDATE_MERGE:
+		submodule_move_head(sub->path, "HEAD", NULL, \
+				    SUBMODULE_MOVE_HEAD_FORCE);
+		break;
+	case SM_UPDATE_NONE:
+	case SM_UPDATE_COMMAND:
+		; /* Do not touch the submodule. */
+	}
+}
+
 /*
  * Remove all cache entries marked for removal, that is where
  * CE_REMOVE is set in ce_flags.  This is much more effective than
@@ -532,8 +550,13 @@ void remove_marked_cache_entries(struct index_state *istate)
 
 	for (i = j = 0; i < istate->cache_nr; i++) {
 		if (ce_array[i]->ce_flags & CE_REMOVE) {
-			remove_name_hash(istate, ce_array[i]);
-			save_or_free_index_entry(istate, ce_array[i]);
+			const struct submodule *sub = submodule_from_ce(ce_array[i]);
+			if (sub) {
+				remove_submodule_according_to_strategy(sub);
+			} else {
+				remove_name_hash(istate, ce_array[i]);
+				save_or_free_index_entry(istate, ce_array[i]);
+			}
 		}
 		else
 			ce_array[j++] = ce_array[i];
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 16/18] entry.c: update submodules when interesting

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 entry.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/entry.c b/entry.c
index c6eea240b6..d2b512da90 100644
--- a/entry.c
+++ b/entry.c
@@ -2,6 +2,7 @@
 #include "blob.h"
 #include "dir.h"
 #include "streaming.h"
+#include "submodule.h"
 
 static void create_directories(const char *path, int path_len,
 			       const struct checkout *state)
@@ -146,6 +147,7 @@ static int write_entry(struct cache_entry *ce,
 	unsigned long size;
 	size_t wrote, newsize = 0;
 	struct stat st;
+	const struct submodule *sub;
 
 	if (ce_mode_s_ifmt == S_IFREG) {
 		struct stream_filter *filter = get_stream_filter(ce->name,
@@ -203,6 +205,10 @@ static int write_entry(struct cache_entry *ce,
 			return error("cannot create temporary submodule %s", path);
 		if (mkdir(path, 0777) < 0)
 			return error("cannot create submodule directory %s", path);
+		sub = submodule_from_ce(ce);
+		if (sub)
+			return submodule_move_head(ce->name,
+				NULL, oid_to_hex(&ce->oid), SUBMODULE_MOVE_HEAD_FORCE);
 		break;
 	default:
 		return error("unknown file mode for %s in index", path);
@@ -259,7 +265,31 @@ int checkout_entry(struct cache_entry *ce,
 	strbuf_add(&path, ce->name, ce_namelen(ce));
 
 	if (!check_path(path.buf, path.len, &st, state->base_dir_len)) {
+		const struct submodule *sub;
 		unsigned changed = ce_match_stat(ce, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
+		/*
+		 * Needs to be checked before !changed returns early,
+		 * as the possibly empty directory was not changed
+		 */
+		sub = submodule_from_ce(ce);
+		if (sub) {
+			int err;
+			if (!is_submodule_populated_gently(ce->name, &err)) {
+				struct stat sb;
+				if (lstat(ce->name, &sb))
+					die(_("could not stat file '%s'"), ce->name);
+				if (!(st.st_mode & S_IFDIR))
+					unlink_or_warn(ce->name);
+
+				return submodule_move_head(ce->name,
+					NULL, oid_to_hex(&ce->oid),
+					SUBMODULE_MOVE_HEAD_FORCE);
+			} else
+				return submodule_move_head(ce->name,
+					"HEAD", oid_to_hex(&ce->oid),
+					SUBMODULE_MOVE_HEAD_FORCE);
+		}
+
 		if (!changed)
 			return 0;
 		if (!state->force) {
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 17/18] builtin/checkout: add --recurse-submodules switch

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/git-checkout.txt |  7 +++++++
 builtin/checkout.c             | 28 ++++++++++++++++++++++++++++
 t/lib-submodule-update.sh      | 23 +++++++++++++++++------
 t/t2013-checkout-submodule.sh  |  5 +++++
 4 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 8e2c0662dd..d6399c0af8 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -256,6 +256,13 @@ section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
 	out anyway. In other words, the ref can be held by more than one
 	worktree.
 
+--[no-]recurse-submodules::
+	Using --recurse-submodules will update the content of all initialized
+	submodules according to the commit recorded in the superproject. If
+	local modifications in a submodule would be overwritten the checkout
+	will fail unless `-f` is used. If nothing (or --no-recurse-submodules)
+	is used, the work trees of submodules will not be updated.
+
 <branch>::
 	Branch to checkout; if it refers to a branch (i.e., a name that,
 	when prepended with "refs/heads/", is a valid ref), then that
diff --git a/builtin/checkout.c b/builtin/checkout.c
index f174f50303..e9c5fcfaf8 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -21,12 +21,31 @@
 #include "submodule-config.h"
 #include "submodule.h"
 
+static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
+
 static const char * const checkout_usage[] = {
 	N_("git checkout [<options>] <branch>"),
 	N_("git checkout [<options>] [<branch>] -- <file>..."),
 	NULL,
 };
 
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
+{
+	if (unset) {
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
 struct checkout_opts {
 	int patch_mode;
 	int quiet;
@@ -1163,6 +1182,9 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 				N_("second guess 'git checkout <no-such-branch>'")),
 		OPT_BOOL(0, "ignore-other-worktrees", &opts.ignore_other_worktrees,
 			 N_("do not check if another worktree is holding the given ref")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules },
 		OPT_BOOL(0, "progress", &opts.show_progress, N_("force progress reporting")),
 		OPT_END(),
 	};
@@ -1193,6 +1215,12 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
 	}
 
+	if (recurse_submodules != RECURSE_SUBMODULES_OFF) {
+		git_config(submodule_config, NULL);
+		if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT)
+			set_config_update_recurse_submodules(recurse_submodules);
+	}
+
 	if ((!!opts.new_branch + !!opts.new_branch_force + !!opts.new_orphan_branch) > 1)
 		die(_("-b, -B and --orphan are mutually exclusive"));
 
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index aa196d4d42..d71972c3db 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -782,6 +782,11 @@ test_submodule_forced_switch () {
 
 test_submodule_switch_recursing () {
 	command="$1"
+	RESULT=success
+	if test "$KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS" = 1
+	then
+		RESULT=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -891,7 +896,7 @@ test_submodule_switch_recursing () {
 	'
 	# Replacing a submodule with files in a directory must succeeds
 	# when the submodule is clean
-	test_expect_success "$command: replace submodule with a directory" '
+	test_expect_$RESULT "$command: replace submodule with a directory" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -903,7 +908,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... absorbing a .git directory.
-	test_expect_success "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
+	test_expect_$RESULT "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -931,7 +936,7 @@ test_submodule_switch_recursing () {
 	'
 
 	# ... must check its local work tree for untracked files
-	test_expect_success "$command: replace submodule with a file must fail with untracked files" '
+	test_expect_$RESULT "$command: replace submodule with a file must fail with untracked files" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -987,7 +992,8 @@ test_submodule_switch_recursing () {
 		)
 	'
 
-	test_expect_success "$command: modified submodule updates submodule recursively" '
+	# recursing deeper than one level doesn't work yet.
+	test_expect_failure "$command: modified submodule updates submodule recursively" '
 		prolog &&
 		reset_work_tree_to_interested add_nested_sub &&
 		(
@@ -1006,6 +1012,11 @@ test_submodule_switch_recursing () {
 # the superproject as well as the submodule is allowed.
 test_submodule_forced_switch_recursing () {
 	command="$1"
+	RESULT=success
+	if test "$KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS" = 1
+	then
+		RESULT=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear creates empty dir ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -1100,7 +1111,7 @@ test_submodule_forced_switch_recursing () {
 		)
 	'
 	# Replacing a submodule with files in a directory ...
-	test_expect_success "$command: replace submodule with a directory" '
+	test_expect_$RESULT "$command: replace submodule with a directory" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -1151,7 +1162,7 @@ test_submodule_forced_switch_recursing () {
 	'
 
 	# ... but stops for untracked files that would be lost
-	test_expect_success "$command: replace submodule with a file" '
+	test_expect_$RESULT "$command: replace submodule with a file stops for untracked files" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
diff --git a/t/t2013-checkout-submodule.sh b/t/t2013-checkout-submodule.sh
index 6847f75822..aa35223369 100755
--- a/t/t2013-checkout-submodule.sh
+++ b/t/t2013-checkout-submodule.sh
@@ -63,6 +63,11 @@ test_expect_success '"checkout <submodule>" honors submodule.*.ignore from .git/
 	! test -s actual
 '
 
+KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+test_submodule_switch_recursing "git checkout --recurse-submodules"
+
+test_submodule_forced_switch_recursing "git checkout -f --recurse-submodules"
+
 test_submodule_switch "git checkout"
 
 test_submodule_forced_switch "git checkout -f"
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 18/18] builtin/read-tree: add --recurse-submodules switch

[Stefan Beller]

A new known failure mode is introduced[1], which is actually not
a failure but a feature in read-tree. Unlike checkout for which
the recursive submodule tests were originally written, read-tree does
warn about ignored untracked files that would be overwritten.
For the sake of keeping the test library for submodules genric, just
mark the test as a failure.

[1] KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/git-read-tree.txt |  6 ++++++
 builtin/read-tree.c             | 29 +++++++++++++++++++++++++++++
 t/lib-submodule-update.sh       |  7 ++++++-
 t/t1013-read-tree-submodule.sh  |  7 +++++++
 4 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt
index fa1d557e5b..ed9d63ef4a 100644
--- a/Documentation/git-read-tree.txt
+++ b/Documentation/git-read-tree.txt
@@ -115,6 +115,12 @@ OPTIONS
 	directories the index file and index output file are
 	located in.
 
+--[no-]recurse-submodules::
+	Using --recurse-submodules will update the content of all initialized
+	submodules according to the commit recorded in the superproject by
+	calling read-tree recursively, also setting the submodules HEAD to be
+	detached at that commit.
+
 --no-sparse-checkout::
 	Disable sparse checkout support even if `core.sparseCheckout`
 	is true.
diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 8ba64bc785..2dc5cc06da 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -15,10 +15,13 @@
 #include "builtin.h"
 #include "parse-options.h"
 #include "resolve-undo.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 static int nr_trees;
 static int read_empty;
 static struct tree *trees[MAX_UNPACK_TREES];
+int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 
 static int list_tree(unsigned char *sha1)
 {
@@ -96,6 +99,23 @@ static int debug_merge(const struct cache_entry * const *stages,
 	return 0;
 }
 
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
+{
+	if (unset) {
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
 static struct lock_file lock_file;
 
 int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
@@ -137,6 +157,9 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 			 N_("skip applying sparse checkout filter")),
 		OPT_BOOL(0, "debug-unpack", &opts.debug_unpack,
 			 N_("debug unpack-trees")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules },
 		OPT_END()
 	};
 
@@ -152,6 +175,12 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 
 	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
 
+	if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT) {
+		gitmodules_config();
+		git_config(submodule_config, NULL);
+		set_config_update_recurse_submodules(RECURSE_SUBMODULES_ON);
+	}
+
 	prefix_set = opts.prefix ? 1 : 0;
 	if (1 < opts.merge + opts.reset + prefix_set)
 		die("Which one? -m, --reset, or --prefix?");
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index d71972c3db..5caae06bc5 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -787,6 +787,11 @@ test_submodule_switch_recursing () {
 	then
 		RESULT=failure
 	fi
+	RESULT1=success
+	if test "$KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED" = 1
+	then
+		RESULT1=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -827,7 +832,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... but an ignored file is fine.
-	test_expect_success "$command: added submodule removes an untracked ignored file" '
+	test_expect_$RESULT1 "$command: added submodule removes an untracked ignored file" '
 		test_when_finished "rm submodule_update/.git/info/exclude" &&
 		prolog &&
 		reset_work_tree_to_interested no_submodule &&
diff --git a/t/t1013-read-tree-submodule.sh b/t/t1013-read-tree-submodule.sh
index 20526aed34..7019d0a04f 100755
--- a/t/t1013-read-tree-submodule.sh
+++ b/t/t1013-read-tree-submodule.sh
@@ -5,6 +5,13 @@ test_description='read-tree can handle submodules'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-submodule-update.sh
 
+KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED=1
+
+test_submodule_switch_recursing "git read-tree --recurse-submodules -u -m"
+
+test_submodule_forced_switch_recursing "git read-tree --recurse-submodules -u --reset"
+
 test_submodule_switch "git read-tree -u -m"
 
 test_submodule_forced_switch "git read-tree -u --reset"
-- 
2.12.0.rc1.52.ge239d7e709.dirty

Re: [PATCH 03/18] lib-submodule-update: teach test_submodule_content the -C <dir> flag

[Eric Wong]

Stefan Beller <sbeller@google.com> wrote:
>  test_submodule_content () {
> +	if test "$1" == "-C"

Use a single '=' for portability in sh.  It's also a good idea
to prefix variables with 'x' or some such, since "$1" could be
"-n" or some other supported switch for test(1).
So, something like:

	if test x"$1" = "x-C"

...or use a case statement.

On Debian systems, I use the "checkbashisms" from the
"devscripts" package to find and avoid bash dependencies.

Thanks.

Re: [PATCH 03/18] lib-submodule-update: teach test_submodule_content the -C <dir> flag

[Stefan Beller]

On Wed, Mar 1, 2017 at 6:11 PM, Eric Wong <e@80x24.org> wrote:
> Stefan Beller <sbeller@google.com> wrote:
>>  test_submodule_content () {
>> +     if test "$1" == "-C"
>
> Use a single '=' for portability in sh.  It's also a good idea
> to prefix variables with 'x' or some such, since "$1" could be
> "-n" or some other supported switch for test(1).
> So, something like:
>
>         if test x"$1" = "x-C"
>
> ...or use a case statement.
>
> On Debian systems, I use the "checkbashisms" from the
> "devscripts" package to find and avoid bash dependencies.

Thanks for review as well as the tip for using
checkbashisms,

I'll resend this series with this fix as well as another fix
in git-submodule.sh

Thanks,
Stefan

Re: [PATCH 03/18] lib-submodule-update: teach test_submodule_content the -C <dir> flag

[Stefan Beller]

On Mon, Mar 6, 2017 at 12:30 PM, Stefan Beller <sbeller@google.com> wrote:
>
> as well as another fix in git-submodule.sh
>

I spoke too early, that seems like a false positive.

[RFCv7 PATCH 00/18] Checkout aware of Submodules!

[Stefan Beller]

previous work:
https://public-inbox.org/git/20170302004759.27852-1-sbeller@google.com
https://public-inbox.org/git/20161203003022.29797-1-sbeller@google.com/

v7:
 * addressed Erics comment by fixing the bashism in t/lib-submodule-update.sh
diff to v6:
  diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
  index 5caae06bc5..949ebd546c 100755
  --- a/t/lib-submodule-update.sh
  +++ b/t/lib-submodule-update.sh
  @@ -255,7 +255,7 @@ test_superproject_content () {
   # Test that the given submodule at path "$1" contains the content according
   # to the submodule commit recorded in the superproject's commit "$2"
   test_submodule_content () {
  -       if test "$1" == "-C"
  +       if test x"$1" = "x-C"
          then
                  cd "$2"
                  shift; shift;
 * interdiff to v5 below
                  

v6:
 * added support for read-tree (see last patch) to see how generic the
   code of the previous patches is. I am pretty pleased with that patch.
 * marked two functions static. Thanks Ramsay!
 * fixed the recursive test; it still fails but it is the code that fails,
   not the test. For this I had to change the setup code slightly.
 * 2 new patches adding tiny refactoring to the submodule test lib.  
 * interdiff (to origin/sb/checkout-recurse-submodules, which is v5) below.

v5:
 * as v4 was the first version queued by Junio, we do have an interdiff below!
 * renamed functions
 * changed the API, now the caller has to take care of the submodule strategy
   themselves. (Note this can be different for different situations, e.g.
   when a submodule is deleted, we can do that for any strategy except none and
   !command. But for moving to a new state of the submodule we currently
   only implement "checkout" [unspecified defaults to checkout]. warning about
   the others, doing nothing there.)

v4:
 * addressed all comments of Brian, Junio and Brandon.
 Thanks!
 * one major point of change is the introduction of another patch
   "lib-submodule-update.sh: do not use ./. as submodule remote",
   as that took some time to track down the existing bug.
 
v3:
 * moved tests from t2013 to the generic submodule library.
 * factored out the refactoring patches to be up front
 * As I redid the complete implementation, I have the impression this time
   it is cleaner than previous versions.
 
 I think we still have to fix the corner cases of directory/file/submodule 
 conflicts before merging, but this serves as a status update on my current
 way of thinking how to implement the worktree commands being aware of
 submodules.
 
Thanks,
Stefan

v2:
* based on top of the series sent out an hour ago
  "[PATCHv4 0/5] submodule embedgitdirs"
* Try to embed a submodule if we need to remove it.
* Strictly do not change behavior if not giving the new flag.
* I think I missed some review comments from v1, but I'd like to get
  the current state out over the weekend, as a lot has changed so far.
  On Monday I'll go through the previous discussion with a comb to see
  if I missed something.
  
v1:
When working with submodules, nearly anytime after checking out
a different state of the projects, that has submodules changed
you'd run "git submodule update" with a current version of Git.

There are two problems with this approach:

* The "submodule update" command is dangerous as it
  doesn't check for work that may be lost in the submodule
  (e.g. a dangling commit).
* you may forget to run the command as checkout is supposed
  to do all the work for you.

Integrate updating the submodules into git checkout, with the same
safety promises that git-checkout has, i.e. not throw away data unless
asked to. This is done by first checking if the submodule is at the same
sha1 as it is recorded in the superproject. If there are changes we stop
proceeding the checkout just like it is when checking out a file that
has local changes.

The integration happens in the code that is also used in other commands
such that it will be easier in the future to make other commands aware
of submodule.

This also solves d/f conflicts in case you replace a file/directory
with a submodule or vice versa.

The patches are still a bit rough, but the overall series seems
promising enough to me that I want to put it out here.

Any review, specifically on the design level welcome!

Thanks,
Stefan


Stefan Beller (14):
  lib-submodule-update.sh: reorder create_lib_submodule_repo
  lib-submodule-update.sh: define tests for recursing into submodules
  make is_submodule_populated gently
  connect_work_tree_and_git_dir: safely create leading directories
  update submodules: add submodule config parsing
  update submodules: add a config option to determine if submodules are
    updated
  update submodules: introduce is_interesting_submodule
  update submodules: move up prepare_submodule_repo_env
  update submodules: add submodule_go_from_to
  unpack-trees: pass old oid to verify_clean_submodule
  unpack-trees: check if we can perform the operation for submodules
  read-cache: remove_marked_cache_entries to wipe selected submodules.
  entry.c: update submodules when interesting
  builtin/checkout: add --recurse-submodules switch
diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt
index fa1d557e5b..ed9d63ef4a 100644
--- a/Documentation/git-read-tree.txt
+++ b/Documentation/git-read-tree.txt
@@ -115,6 +115,12 @@ OPTIONS
 	directories the index file and index output file are
 	located in.
 
+--[no-]recurse-submodules::
+	Using --recurse-submodules will update the content of all initialized
+	submodules according to the commit recorded in the superproject by
+	calling read-tree recursively, also setting the submodules HEAD to be
+	detached at that commit.
+
 --no-sparse-checkout::
 	Disable sparse checkout support even if `core.sparseCheckout`
 	is true.
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 207ce09771..e9c5fcfaf8 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -29,8 +29,8 @@ static const char * const checkout_usage[] = {
 	NULL,
 };
 
-int option_parse_recurse_submodules(const struct option *opt,
-				    const char *arg, int unset)
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
 {
 	if (unset) {
 		recurse_submodules = RECURSE_SUBMODULES_OFF;
diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 8ba64bc785..2dc5cc06da 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -15,10 +15,13 @@
 #include "builtin.h"
 #include "parse-options.h"
 #include "resolve-undo.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 static int nr_trees;
 static int read_empty;
 static struct tree *trees[MAX_UNPACK_TREES];
+int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 
 static int list_tree(unsigned char *sha1)
 {
@@ -96,6 +99,23 @@ static int debug_merge(const struct cache_entry * const *stages,
 	return 0;
 }
 
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
+{
+	if (unset) {
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
 static struct lock_file lock_file;
 
 int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
@@ -137,6 +157,9 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 			 N_("skip applying sparse checkout filter")),
 		OPT_BOOL(0, "debug-unpack", &opts.debug_unpack,
 			 N_("debug unpack-trees")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules },
 		OPT_END()
 	};
 
@@ -152,6 +175,12 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 
 	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
 
+	if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT) {
+		gitmodules_config();
+		git_config(submodule_config, NULL);
+		set_config_update_recurse_submodules(RECURSE_SUBMODULES_ON);
+	}
+
 	prefix_set = opts.prefix ? 1 : 0;
 	if (1 < opts.merge + opts.reset + prefix_set)
 		die("Which one? -m, --reset, or --prefix?");
diff --git a/submodule.c b/submodule.c
index a2cf8c9376..bc5fecf8c5 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1257,7 +1257,7 @@ static int submodule_has_dirty_index(const struct submodule *sub)
 	return finish_command(&cp);
 }
 
-void submodule_reset_index(const char *path)
+static void submodule_reset_index(const char *path)
 {
 	struct child_process cp = CHILD_PROCESS_INIT;
 	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 54cd8a6366..429cd1041d 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -4,7 +4,7 @@
 # - New submodule (no_submodule => add_sub1)
 # - Removed submodule (add_sub1 => remove_sub1)
 # - Updated submodule (add_sub1 => modify_sub1)
-# - Updated submodule recursively (modify_sub1 => modify_sub1_recursively)
+# - Updated submodule recursively (add_nested_sub => modify_sub1_recursively)
 # - Submodule updated to invalid commit (add_sub1 => invalid_sub1)
 # - Submodule updated from invalid commit (invalid_sub1 => valid_sub1)
 # - Submodule replaced by tracked files in directory (add_sub1 =>
@@ -20,8 +20,8 @@
 #                    /    ^
 #                   /     remove_sub1
 #                  /
-#       add_sub1  /-------O---------O
-#             |  /        ^         modify_sub1_recursive
+#       add_sub1  /-------O---------O--------O  modify_sub1_recursively
+#             |  /        ^         add_nested_sub
 #             | /         modify_sub1
 #             v/
 #      O------O-----------O---------O
@@ -96,12 +96,24 @@ create_lib_submodule_repo () {
 		git add sub1 &&
 		git commit -m "Modify sub1" &&
 
-		git checkout -b modify_sub1_recursively modify_sub1 &&
+		git checkout -b add_nested_sub modify_sub1 &&
 		git -C sub1 checkout -b "add_nested_sub" &&
 		git -C sub1 submodule add --branch no_submodule ../submodule_update_sub2 sub2 &&
 		git -C sub1 commit -a -m "add a nested submodule" &&
 		git add sub1 &&
 		git commit -a -m "update submodule, that updates a nested submodule" &&
+		git checkout -b modify_sub1_recursively &&
+		git -C sub1 checkout -b modify_sub1_recursively &&
+		git -C sub1/sub2 checkout -b modify_sub1_recursively &&
+		echo change >sub1/sub2/file3 &&
+		git -C sub1/sub2 add file3 &&
+		git -C sub1/sub2 commit -m "make a change in nested sub" &&
+		git -C sub1 add sub2 &&
+		git -C sub1 commit -m "update nested sub" &&
+		git add sub1 &&
+		git commit -m "update sub1, that updates nested sub" &&
+		git -C sub1 push origin modify_sub1_recursively &&
+		git -C sub1/sub2 push origin modify_sub1_recursively &&
 		git -C sub1 submodule deinit -f --all &&
 
 		git checkout -b replace_sub1_with_directory add_sub1 &&
@@ -200,9 +212,9 @@ reset_work_tree_to () {
 		git checkout -f "$1" &&
 		git status -u -s >actual &&
 		test_must_be_empty actual &&
-		sha1=$(git rev-parse --revs-only HEAD:sub1) &&
-		if test -n "$sha1" &&
-		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$sha1^{commit}")
+		hash=$(git rev-parse --revs-only HEAD:sub1) &&
+		if test -n "$hash" &&
+		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$hash^{commit}")
 		then
 			git submodule update --init --recursive "sub1"
 		fi
@@ -211,14 +223,23 @@ reset_work_tree_to () {
 
 reset_work_tree_to_interested () {
 	reset_work_tree_to $1 &&
-	# indicate we are interested in the submodule:
-	git -C submodule_update config submodule.sub1.url "bogus" &&
-	# also have it available:
+	# make the submodule git dirs available
 	if ! test -d submodule_update/.git/modules/sub1
 	then
 		mkdir -p submodule_update/.git/modules &&
 		cp -r submodule_update_repo/.git/modules/sub1 submodule_update/.git/modules/sub1
-	fi
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1 config --unset core.worktree
+	fi &&
+	if ! test -d submodule_update/.git/modules/sub1/modules/sub2
+	then
+		mkdir -p submodule_update/.git/modules/sub1/modules &&
+		cp -r submodule_update_repo/.git/modules/sub1/modules/sub2 submodule_update/.git/modules/sub1/modules/sub2
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1/modules/sub2 config --unset core.worktree
+	fi &&
+	# indicate we are interested in the submodule:
+	git -C submodule_update config submodule.sub1.url "bogus" &&
+	# sub1 might not be checked out, so use the git dir
+	git -C submodule_update/.git/modules/sub1 config submodule.sub2.url "bogus"
 }
 
 # Test that the superproject contains the content according to commit "$1"
@@ -234,6 +255,11 @@ test_superproject_content () {
 # Test that the given submodule at path "$1" contains the content according
 # to the submodule commit recorded in the superproject's commit "$2"
 test_submodule_content () {
+	if test x"$1" == "x-C"
+	then
+		cd "$2"
+		shift; shift;
+	fi
 	if test $# != 2
 	then
 		echo "test_submodule_content needs two arguments"
@@ -761,6 +787,11 @@ test_submodule_switch_recursing () {
 	then
 		RESULT=failure
 	fi
+
+	if test "$KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED" = 1
+	then
+		RESULT1=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -801,7 +832,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... but an ignored file is fine.
-	test_expect_success "$command: added submodule removes an untracked ignored file" '
+	test_expect_$RESULT1 "$command: added submodule removes an untracked ignored file" '
 		test_when_finished "rm submodule_update/.git/info/exclude" &&
 		prolog &&
 		reset_work_tree_to_interested no_submodule &&
@@ -966,21 +997,17 @@ test_submodule_switch_recursing () {
 		)
 	'
 
-	# This test fails, due to missing setup, we do not clone sub2 into
-	# submodule_update, because it doesn't exist in the 'add_sub1' version
-	#
-	test_expect_success "$command: modified submodule updates submodule recursively" '
+	# recursing deeper than one level doesn't work yet.
+	test_expect_failure "$command: modified submodule updates submodule recursively" '
 		prolog &&
-		reset_work_tree_to_interested add_sub1 &&
+		reset_work_tree_to_interested add_nested_sub &&
 		(
 			cd submodule_update &&
 			git branch -t modify_sub1_recursively origin/modify_sub1_recursively &&
-			test_must_fail $command modify_sub1_recursively &&
-			test_superproject_content origin/add_sub1 &&
-			test_submodule_content sub1 origin/add_sub1
-			# test_superproject_content origin/modify_sub1_recursively &&
-			# test_submodule_content sub1 origin/modify_sub1_recursively &&
-			# test_submodule_content sub1/sub2 no_submodule
+			$command modify_sub1_recursively &&
+			test_superproject_content origin/modify_sub1_recursively &&
+			test_submodule_content sub1 origin/modify_sub1_recursively &&
+			test_submodule_content -C sub1 sub2 origin/modify_sub1_recursively
 		)
 	'
 }
diff --git a/t/t1013-read-tree-submodule.sh b/t/t1013-read-tree-submodule.sh
index 20526aed34..7019d0a04f 100755
--- a/t/t1013-read-tree-submodule.sh
+++ b/t/t1013-read-tree-submodule.sh
@@ -5,6 +5,13 @@ test_description='read-tree can handle submodules'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-submodule-update.sh
 
+KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED=1
+
+test_submodule_switch_recursing "git read-tree --recurse-submodules -u -m"
+
+test_submodule_forced_switch_recursing "git read-tree --recurse-submodules -u --reset"
+
 test_submodule_switch "git read-tree -u -m"
 
 test_submodule_forced_switch "git read-tree -u --reset"

[PATCH 01/18] lib-submodule-update.sh: reorder create_lib_submodule_repo

[Stefan Beller]

Redraw the ASCII art describing the setup using more space, such that
it is easier to understand.  The leaf commits are now ordered the same
way the actual code is ordered.

Add empty lines to the setup code separating each of the leaf commits,
each starting with a "checkout -b".

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 49 ++++++++++++++++++++++++++++-------------------
 1 file changed, 29 insertions(+), 20 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 915eb4a7c6..5df528ea81 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -15,22 +15,27 @@
 # - Tracked file replaced by submodule (replace_sub1_with_file =>
 #   replace_file_with_sub1)
 #
-#                   --O-----O
-#                  /  ^     replace_directory_with_sub1
-#                 /   replace_sub1_with_directory
-#                /----O
-#               /     ^
-#              /      modify_sub1
-#      O------O-------O
-#      ^      ^\      ^
-#      |      | \     remove_sub1
-#      |      |  -----O-----O
-#      |      |   \   ^     replace_file_with_sub1
-#      |      |    \  replace_sub1_with_file
-#      |   add_sub1 --O-----O
-# no_submodule        ^     valid_sub1
-#                     invalid_sub1
+#                     ----O
+#                    /    ^
+#                   /     remove_sub1
+#                  /
+#       add_sub1  /-------O
+#             |  /        ^
+#             | /         modify_sub1
+#             v/
+#      O------O-----------O---------O
+#      ^       \          ^         replace_directory_with_sub1
+#      |        \         replace_sub1_with_directory
+# no_submodule   \
+#                 --------O---------O
+#                  \      ^         replace_file_with_sub1
+#                   \     replace_sub1_with_file
+#                    \
+#                     ----O---------O
+#                         ^         valid_sub1
+#                         invalid_sub1
 #
+
 create_lib_submodule_repo () {
 	git init submodule_update_repo &&
 	(
@@ -49,10 +54,11 @@ create_lib_submodule_repo () {
 		git config submodule.sub1.ignore all &&
 		git add .gitmodules &&
 		git commit -m "Add sub1" &&
-		git checkout -b remove_sub1 &&
+
+		git checkout -b remove_sub1 add_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "modify_sub1" "add_sub1" &&
+		git checkout -b modify_sub1 add_sub1 &&
 		git submodule update &&
 		(
 			cd sub1 &&
@@ -67,7 +73,7 @@ create_lib_submodule_repo () {
 		git add sub1 &&
 		git commit -m "Modify sub1" &&
 
-		git checkout -b "replace_sub1_with_directory" "add_sub1" &&
+		git checkout -b replace_sub1_with_directory add_sub1 &&
 		git submodule update &&
 		git -C sub1 checkout modifications &&
 		git rm --cached sub1 &&
@@ -75,22 +81,25 @@ create_lib_submodule_repo () {
 		git config -f .gitmodules --remove-section "submodule.sub1" &&
 		git add .gitmodules sub1/* &&
 		git commit -m "Replace sub1 with directory" &&
+
 		git checkout -b replace_directory_with_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "replace_sub1_with_file" "add_sub1" &&
+		git checkout -b replace_sub1_with_file add_sub1 &&
 		git rm sub1 &&
 		echo "content" >sub1 &&
 		git add sub1 &&
 		git commit -m "Replace sub1 with file" &&
+
 		git checkout -b replace_file_with_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "invalid_sub1" "add_sub1" &&
+		git checkout -b invalid_sub1 add_sub1 &&
 		git update-index --cacheinfo 160000 0123456789012345678901234567890123456789 sub1 &&
 		git commit -m "Invalid sub1 commit" &&
 		git checkout -b valid_sub1 &&
 		git revert HEAD &&
+
 		git checkout master
 	)
 }
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 02/18] lib-submodule-update.sh: do not use ./. as submodule remote

[Stefan Beller]

Adding the repository itself as a submodule does not make sense in the
real world. In our test suite we used to do that out of convenience in
some tests as the current repository has easiest access for setting up
'just a submodule'.

However this doesn't quite test the real world, so let's do not follow
this pattern any further and actually create an independent repository
that we can use as a submodule.

When using './.' as the remote the superproject and submodule share the
same objects, such that testing if a given sha1 is a valid commit works
in either repository.  As running commands in an unpopulated submodule
fall back to the superproject, this happens in `reset_work_tree_to`
to determine if we need to populate the submodule. Fix this bug by
checking in the actual remote now.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 5df528ea81..c0d6325133 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -37,6 +37,17 @@
 #
 
 create_lib_submodule_repo () {
+	git init submodule_update_sub1 &&
+	(
+		cd submodule_update_sub1 &&
+		echo "expect" >>.gitignore &&
+		echo "actual" >>.gitignore &&
+		echo "x" >file1 &&
+		echo "y" >file2 &&
+		git add .gitignore file1 file2 &&
+		git commit -m "Base inside first submodule" &&
+		git branch "no_submodule"
+	) &&
 	git init submodule_update_repo &&
 	(
 		cd submodule_update_repo &&
@@ -49,7 +60,7 @@ create_lib_submodule_repo () {
 		git branch "no_submodule" &&
 
 		git checkout -b "add_sub1" &&
-		git submodule add ./. sub1 &&
+		git submodule add ../submodule_update_sub1 sub1 &&
 		git config -f .gitmodules submodule.sub1.ignore all &&
 		git config submodule.sub1.ignore all &&
 		git add .gitmodules &&
@@ -162,7 +173,7 @@ reset_work_tree_to () {
 		test_must_be_empty actual &&
 		sha1=$(git rev-parse --revs-only HEAD:sub1) &&
 		if test -n "$sha1" &&
-		   test $(cd "sub1" && git rev-parse --verify "$sha1^{commit}")
+		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$sha1^{commit}")
 		then
 			git submodule update --init --recursive "sub1"
 		fi
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 03/18] lib-submodule-update: teach test_submodule_content the -C <dir> flag

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index c0d6325133..00128f28b5 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -193,6 +193,11 @@ test_superproject_content () {
 # Test that the given submodule at path "$1" contains the content according
 # to the submodule commit recorded in the superproject's commit "$2"
 test_submodule_content () {
+	if test x"$1" = "x-C"
+	then
+		cd "$2"
+		shift; shift;
+	fi
 	if test $# != 2
 	then
 		echo "test_submodule_content needs two arguments"
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 04/18] lib-submodule-update.sh: replace sha1 by hash

[Stefan Beller]

Cleaning up code by generalising it.
Currently the mailing list discusses yet again how
to migrate away from sha1.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 00128f28b5..f52c49c838 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -171,9 +171,9 @@ reset_work_tree_to () {
 		git checkout -f "$1" &&
 		git status -u -s >actual &&
 		test_must_be_empty actual &&
-		sha1=$(git rev-parse --revs-only HEAD:sub1) &&
-		if test -n "$sha1" &&
-		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$sha1^{commit}")
+		hash=$(git rev-parse --revs-only HEAD:sub1) &&
+		if test -n "$hash" &&
+		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$hash^{commit}")
 		then
 			git submodule update --init --recursive "sub1"
 		fi
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 05/18] lib-submodule-update.sh: define tests for recursing into submodules

[Stefan Beller]

Currently lib-submodule-update.sh provides 2 functions
test_submodule_switch and test_submodule_forced_switch that are used by a
variety of tests to ensure that submodules behave as expected. The current
expected behavior is that submodules are not touched at all (see
42639d2317a for the exact setup).

In the future we want to teach all these commands to recurse
into submodules. To do that, we'll add two testing functions to
submodule-update-lib.sh: test_submodule_switch_recursing and
test_submodule_forced_switch_recursing.

These two functions behave in analogy to the already existing functions
just with a different expectation on submodule behavior. The submodule
in the working tree is expected to be updated to the recorded submodule
version. The behavior is analogous to e.g. the behavior of files in a
nested directory in the working tree, where a change to the working tree
handles any arising directory/file conflicts just fine.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 506 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 504 insertions(+), 2 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index f52c49c838..5b885cfbf8 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -4,6 +4,7 @@
 # - New submodule (no_submodule => add_sub1)
 # - Removed submodule (add_sub1 => remove_sub1)
 # - Updated submodule (add_sub1 => modify_sub1)
+# - Updated submodule recursively (add_nested_sub => modify_sub1_recursively)
 # - Submodule updated to invalid commit (add_sub1 => invalid_sub1)
 # - Submodule updated from invalid commit (invalid_sub1 => valid_sub1)
 # - Submodule replaced by tracked files in directory (add_sub1 =>
@@ -19,8 +20,8 @@
 #                    /    ^
 #                   /     remove_sub1
 #                  /
-#       add_sub1  /-------O
-#             |  /        ^
+#       add_sub1  /-------O---------O--------O  modify_sub1_recursively
+#             |  /        ^         add_nested_sub
 #             | /         modify_sub1
 #             v/
 #      O------O-----------O---------O
@@ -48,6 +49,17 @@ create_lib_submodule_repo () {
 		git commit -m "Base inside first submodule" &&
 		git branch "no_submodule"
 	) &&
+	git init submodule_update_sub2 &&
+	(
+		cd submodule_update_sub2
+		echo "expect" >>.gitignore &&
+		echo "actual" >>.gitignore &&
+		echo "x" >file1 &&
+		echo "y" >file2 &&
+		git add .gitignore file1 file2 &&
+		git commit -m "nested submodule base" &&
+		git branch "no_submodule"
+	) &&
 	git init submodule_update_repo &&
 	(
 		cd submodule_update_repo &&
@@ -84,6 +96,26 @@ create_lib_submodule_repo () {
 		git add sub1 &&
 		git commit -m "Modify sub1" &&
 
+		git checkout -b add_nested_sub modify_sub1 &&
+		git -C sub1 checkout -b "add_nested_sub" &&
+		git -C sub1 submodule add --branch no_submodule ../submodule_update_sub2 sub2 &&
+		git -C sub1 commit -a -m "add a nested submodule" &&
+		git add sub1 &&
+		git commit -a -m "update submodule, that updates a nested submodule" &&
+		git checkout -b modify_sub1_recursively &&
+		git -C sub1 checkout -b modify_sub1_recursively &&
+		git -C sub1/sub2 checkout -b modify_sub1_recursively &&
+		echo change >sub1/sub2/file3 &&
+		git -C sub1/sub2 add file3 &&
+		git -C sub1/sub2 commit -m "make a change in nested sub" &&
+		git -C sub1 add sub2 &&
+		git -C sub1 commit -m "update nested sub" &&
+		git add sub1 &&
+		git commit -m "update sub1, that updates nested sub" &&
+		git -C sub1 push origin modify_sub1_recursively &&
+		git -C sub1/sub2 push origin modify_sub1_recursively &&
+		git -C sub1 submodule deinit -f --all &&
+
 		git checkout -b replace_sub1_with_directory add_sub1 &&
 		git submodule update &&
 		git -C sub1 checkout modifications &&
@@ -150,6 +182,15 @@ test_git_directory_is_unchanged () {
 	)
 }
 
+test_git_directory_exists() {
+	test -e ".git/modules/$1" &&
+	if test -f sub1/.git
+	then
+		# does core.worktree point at the right place?
+		test "$(git -C .git/modules/$1 config core.worktree)" = "../../../$1"
+	fi
+}
+
 # Helper function to be executed at the start of every test below, it sets up
 # the submodule repo if it doesn't exist and configures the most problematic
 # settings for diff.ignoreSubmodules.
@@ -180,6 +221,27 @@ reset_work_tree_to () {
 	)
 }
 
+reset_work_tree_to_interested () {
+	reset_work_tree_to $1 &&
+	# make the submodule git dirs available
+	if ! test -d submodule_update/.git/modules/sub1
+	then
+		mkdir -p submodule_update/.git/modules &&
+		cp -r submodule_update_repo/.git/modules/sub1 submodule_update/.git/modules/sub1
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1 config --unset core.worktree
+	fi &&
+	if ! test -d submodule_update/.git/modules/sub1/modules/sub2
+	then
+		mkdir -p submodule_update/.git/modules/sub1/modules &&
+		cp -r submodule_update_repo/.git/modules/sub1/modules/sub2 submodule_update/.git/modules/sub1/modules/sub2
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1/modules/sub2 config --unset core.worktree
+	fi &&
+	# indicate we are interested in the submodule:
+	git -C submodule_update config submodule.sub1.url "bogus" &&
+	# sub1 might not be checked out, so use the git dir
+	git -C submodule_update/.git/modules/sub1 config submodule.sub2.url "bogus"
+}
+
 # Test that the superproject contains the content according to commit "$1"
 # (the work tree must match the index for everything but submodules but the
 # index must exactly match the given commit including any submodule SHA-1s).
@@ -700,3 +762,443 @@ test_submodule_forced_switch () {
 		)
 	'
 }
+
+# Test that submodule contents are correctly updated when switching
+# between commits that change a submodule.
+# Test that the following transitions are correctly handled:
+# (These tests are also above in the case where we expect no change
+#  in the submodule)
+# - Updated submodule
+# - New submodule
+# - Removed submodule
+# - Directory containing tracked files replaced by submodule
+# - Submodule replaced by tracked files in directory
+# - Submodule replaced by tracked file with the same name
+# - tracked file replaced by submodule
+#
+# New test cases
+# - Removing a submodule with a git directory absorbs the submodules
+#   git directory first into the superproject.
+
+test_submodule_switch_recursing () {
+	command="$1"
+	######################### Appearing submodule #########################
+	# Switching to a commit letting a submodule appear checks it out ...
+	test_expect_success "$command: added submodule is checked out" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... ignoring an empty existing directory ...
+	test_expect_success "$command: added submodule is checked out in empty dir" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			mkdir sub1 &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... unless there is an untracked file in its place.
+	test_expect_success "$command: added submodule doesn't remove untracked file with same name" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			: >sub1 &&
+			test_must_fail $command add_sub1 &&
+			test_superproject_content origin/no_submodule &&
+			test_must_be_empty sub1
+		)
+	'
+	# ... but an ignored file is fine.
+	test_expect_success "$command: added submodule removes an untracked ignored file" '
+		test_when_finished "rm submodule_update/.git/info/exclude" &&
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			: >sub1 &&
+			echo sub1 >.git/info/exclude
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Replacing a tracked file with a submodule produces a checked out submodule
+	test_expect_success "$command: replace tracked file with submodule checks out submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_file &&
+		(
+			cd submodule_update &&
+			git branch -t replace_file_with_sub1 origin/replace_file_with_sub1 &&
+			$command replace_file_with_sub1 &&
+			test_superproject_content origin/replace_file_with_sub1 &&
+			test_submodule_content sub1 origin/replace_file_with_sub1
+		)
+	'
+	# ... as does removing a directory with tracked files with a submodule.
+	test_expect_success "$command: replace directory with submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_directory &&
+		(
+			cd submodule_update &&
+			git branch -t replace_directory_with_sub1 origin/replace_directory_with_sub1 &&
+			$command replace_directory_with_sub1 &&
+			test_superproject_content origin/replace_directory_with_sub1 &&
+			test_submodule_content sub1 origin/replace_directory_with_sub1
+		)
+	'
+
+	######################## Disappearing submodule #######################
+	# Removing a submodule removes its work tree ...
+	test_expect_success "$command: removed submodule removes submodules working tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1
+		)
+	'
+	# ... absorbing a .git directory along the way.
+	test_expect_success "$command: removed submodule absorbs submodules .git directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1 &&
+			test_git_directory_exists sub1
+		)
+	'
+	# Replacing a submodule with files in a directory must succeeds
+	# when the submodule is clean
+	test_expect_success "$command: replace submodule with a directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_submodule_content sub1 origin/replace_sub1_with_directory
+		)
+	'
+	# ... absorbing a .git directory.
+	test_expect_success "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_git_directory_exists sub1
+		)
+	'
+
+	# Replacing it with a file ...
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file &&
+			test -f sub1
+		)
+	'
+
+	# ... must check its local work tree for untracked files
+	test_expect_success "$command: replace submodule with a file must fail with untracked files" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/untrackedfile &&
+			test_must_fail $command replace_sub1_with_file &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+
+	# ... and ignored files are ignroed
+	test_expect_success "$command: replace submodule with a file works ignores ignored files in submodule" '
+		test_when_finished "rm submodule_update/.git/modules/sub1/info/exclude" &&
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/ignored &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file &&
+			test -f sub1
+		)
+	'
+
+	########################## Modified submodule #########################
+	# Updating a submodule sha1 updates the submodule's work tree
+	test_expect_success "$command: modified submodule updates submodule work tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1 origin/modify_sub1 &&
+			$command modify_sub1 &&
+			test_superproject_content origin/modify_sub1 &&
+			test_submodule_content sub1 origin/modify_sub1
+		)
+	'
+
+	# Updating a submodule to an invalid sha1 doesn't update the
+	# superproject nor the submodule's work tree.
+	test_expect_success "$command: updating to a missing submodule commit fails" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t invalid_sub1 origin/invalid_sub1 &&
+			test_must_fail $command invalid_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+
+	test_expect_success "$command: modified submodule updates submodule recursively" '
+		prolog &&
+		reset_work_tree_to_interested add_nested_sub &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1_recursively origin/modify_sub1_recursively &&
+			$command modify_sub1_recursively &&
+			test_superproject_content origin/modify_sub1_recursively &&
+			test_submodule_content sub1 origin/modify_sub1_recursively &&
+			test_submodule_content -C sub1 sub2 origin/modify_sub1_recursively
+		)
+	'
+}
+
+# Test that submodule contents are updated when switching between commits
+# that change a submodule, but throwing away local changes in
+# the superproject as well as the submodule is allowed.
+test_submodule_forced_switch_recursing () {
+	command="$1"
+	######################### Appearing submodule #########################
+	# Switching to a commit letting a submodule appear creates empty dir ...
+	test_expect_success "$command: added submodule is checked out" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... and doesn't care if it already exists ...
+	test_expect_success "$command: added submodule ignores empty directory" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			mkdir sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... not caring about an untracked file either
+	test_expect_success "$command: added submodule does remove untracked unignored file with same name when forced" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			>sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Replacing a tracked file with a submodule checks out the submodule
+	test_expect_success "$command: replace tracked file with submodule populates the submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_file &&
+		(
+			cd submodule_update &&
+			git branch -t replace_file_with_sub1 origin/replace_file_with_sub1 &&
+			$command replace_file_with_sub1 &&
+			test_superproject_content origin/replace_file_with_sub1 &&
+			test_submodule_content sub1 origin/replace_file_with_sub1
+		)
+	'
+	# ... as does removing a directory with tracked files with a
+	# submodule.
+	test_expect_success "$command: replace directory with submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_directory &&
+		(
+			cd submodule_update &&
+			git branch -t replace_directory_with_sub1 origin/replace_directory_with_sub1 &&
+			$command replace_directory_with_sub1 &&
+			test_superproject_content origin/replace_directory_with_sub1 &&
+			test_submodule_content sub1 origin/replace_directory_with_sub1
+		)
+	'
+
+	######################## Disappearing submodule #######################
+	# Removing a submodule doesn't remove its work tree ...
+	test_expect_success "$command: removed submodule leaves submodule directory and its contents in place" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1
+		)
+	'
+	# ... especially when it contains a .git directory.
+	test_expect_success "$command: removed submodule leaves submodule containing a .git directory alone" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules/sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			test_git_directory_exists sub1 &&
+			! test -e sub1
+		)
+	'
+	# Replacing a submodule with files in a directory ...
+	test_expect_success "$command: replace submodule with a directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			test_must_fail $command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory
+		)
+	'
+	# ... absorbing a .git directory.
+	test_expect_success "$command: replace submodule containing a .git directory with a directory must fail" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules/sub1 &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_submodule_content sub1 origin/modify_sub1
+			test_git_directory_exists sub1
+		)
+	'
+	# Replacing it with a file
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file
+		)
+	'
+
+	# ... even if the submodule contains ignored files
+	test_expect_success "$command: replace submodule with a file ignoring ignored files" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/expect &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file
+		)
+	'
+
+	# ... but stops for untracked files that would be lost
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/untracked_file &&
+			test_must_fail $command replace_sub1_with_file &&
+			test_superproject_content origin/add_sub1 &&
+			test -f sub1/untracked_file
+		)
+	'
+
+	########################## Modified submodule #########################
+	# Updating a submodule sha1 updates the submodule's work tree
+	test_expect_success "$command: modified submodule updates submodule work tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1 origin/modify_sub1 &&
+			$command modify_sub1 &&
+			test_superproject_content origin/modify_sub1 &&
+			test_submodule_content sub1 origin/modify_sub1
+		)
+	'
+	# Updating a submodule to an invalid sha1 doesn't update the
+	# submodule's work tree, subsequent update will fail
+	test_expect_success "$command: modified submodule does not update submodule work tree to invalid commit" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t invalid_sub1 origin/invalid_sub1 &&
+			test_must_fail $command invalid_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Updating a submodule from an invalid sha1 updates
+	test_expect_success "$command: modified submodule does not update submodule work tree from invalid commit" '
+		prolog &&
+		reset_work_tree_to_interested invalid_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t valid_sub1 origin/valid_sub1 &&
+			test_must_fail $command valid_sub1 &&
+			test_superproject_content origin/invalid_sub1
+		)
+	'
+}
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 06/18] make is_submodule_populated gently

[Stefan Beller]

We need the gentle version in a later patch. As we have just one caller,
migrate the caller.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/grep.c | 2 +-
 submodule.c    | 7 ++-----
 submodule.h    | 8 +++++++-
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/builtin/grep.c b/builtin/grep.c
index 2c727ef499..b17835aed6 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -616,7 +616,7 @@ static int grep_submodule(struct grep_opt *opt, const unsigned char *sha1,
 {
 	if (!is_submodule_initialized(path))
 		return 0;
-	if (!is_submodule_populated(path)) {
+	if (!is_submodule_populated_gently(path, NULL)) {
 		/*
 		 * If searching history, check for the presense of the
 		 * submodule's gitdir before skipping the submodule.
diff --git a/submodule.c b/submodule.c
index 3b98766a6b..0e55372f37 100644
--- a/submodule.c
+++ b/submodule.c
@@ -234,15 +234,12 @@ int is_submodule_initialized(const char *path)
 	return ret;
 }
 
-/*
- * Determine if a submodule has been populated at a given 'path'
- */
-int is_submodule_populated(const char *path)
+int is_submodule_populated_gently(const char *path, int *return_error_code)
 {
 	int ret = 0;
 	char *gitdir = xstrfmt("%s/.git", path);
 
-	if (resolve_gitdir(gitdir))
+	if (resolve_gitdir_gently(gitdir, return_error_code))
 		ret = 1;
 
 	free(gitdir);
diff --git a/submodule.h b/submodule.h
index 05ab674f06..0b915bd3ac 100644
--- a/submodule.h
+++ b/submodule.h
@@ -41,7 +41,13 @@ extern int submodule_config(const char *var, const char *value, void *cb);
 extern void gitmodules_config(void);
 extern void gitmodules_config_sha1(const unsigned char *commit_sha1);
 extern int is_submodule_initialized(const char *path);
-extern int is_submodule_populated(const char *path);
+/*
+ * Determine if a submodule has been populated at a given 'path' by checking if
+ * the <path>/.git resolves to a valid git repository.
+ * If return_error_code is NULL, die on error.
+ * Otherwise the return error code is the same as of resolve_gitdir_gently.
+ */
+extern int is_submodule_populated_gently(const char *path, int *return_error_code);
 extern int parse_submodule_update_strategy(const char *value,
 		struct submodule_update_strategy *dst);
 extern const char *submodule_strategy_to_string(const struct submodule_update_strategy *s);
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 07/18] connect_work_tree_and_git_dir: safely create leading directories

[Stefan Beller]

In a later patch we'll use connect_work_tree_and_git_dir when the
directory for the gitlink file doesn't exist yet. This patch makes
connect_work_tree_and_git_dir safe to use for both cases of
either the git dir or the working dir missing.

To do so, we need to call safe_create_leading_directories[_const]
on both directories. However this has to happen before we construct
the absolute paths as real_pathdup assumes the directories to
be there already.

So for both the config file in the git dir as well as the .git link
file we need to
a) construct the name
b) call SCLD
c) get the absolute path
d) once a-c is done for both we can consume the absolute path
   to compute the relative path to each other and store those
   relative paths.

The implementation provided here puts a) and b) for both cases first,
and then performs c and d after.

One of the two users of 'connect_work_tree_and_git_dir' already checked
for the directory being there, so we can loose that check as
connect_work_tree_and_git_dir handles this functionality now.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 dir.c       | 32 +++++++++++++++++++++-----------
 submodule.c | 11 ++---------
 2 files changed, 23 insertions(+), 20 deletions(-)

diff --git a/dir.c b/dir.c
index 4541f9e146..6f52af7abb 100644
--- a/dir.c
+++ b/dir.c
@@ -2728,23 +2728,33 @@ void untracked_cache_add_to_index(struct index_state *istate,
 /* Update gitfile and core.worktree setting to connect work tree and git dir */
 void connect_work_tree_and_git_dir(const char *work_tree_, const char *git_dir_)
 {
-	struct strbuf file_name = STRBUF_INIT;
+	struct strbuf gitfile_sb = STRBUF_INIT;
+	struct strbuf cfg_sb = STRBUF_INIT;
 	struct strbuf rel_path = STRBUF_INIT;
-	char *git_dir = real_pathdup(git_dir_);
-	char *work_tree = real_pathdup(work_tree_);
+	char *git_dir, *work_tree;
 
-	/* Update gitfile */
-	strbuf_addf(&file_name, "%s/.git", work_tree);
-	write_file(file_name.buf, "gitdir: %s",
-		   relative_path(git_dir, work_tree, &rel_path));
+	/* Prepare .git file */
+	strbuf_addf(&gitfile_sb, "%s/.git", work_tree_);
+	if (safe_create_leading_directories_const(gitfile_sb.buf))
+		die(_("could not create directories for %s"), gitfile_sb.buf);
+
+	/* Prepare config file */
+	strbuf_addf(&cfg_sb, "%s/config", git_dir_);
+	if (safe_create_leading_directories_const(cfg_sb.buf))
+		die(_("could not create directories for %s"), cfg_sb.buf);
 
+	git_dir = real_pathdup(git_dir_);
+	work_tree = real_pathdup(work_tree_);
+
+	/* Write .git file */
+	write_file(gitfile_sb.buf, "gitdir: %s",
+		   relative_path(git_dir, work_tree, &rel_path));
 	/* Update core.worktree setting */
-	strbuf_reset(&file_name);
-	strbuf_addf(&file_name, "%s/config", git_dir);
-	git_config_set_in_file(file_name.buf, "core.worktree",
+	git_config_set_in_file(cfg_sb.buf, "core.worktree",
 			       relative_path(work_tree, git_dir, &rel_path));
 
-	strbuf_release(&file_name);
+	strbuf_release(&gitfile_sb);
+	strbuf_release(&cfg_sb);
 	strbuf_release(&rel_path);
 	free(work_tree);
 	free(git_dir);
diff --git a/submodule.c b/submodule.c
index 0e55372f37..04d185738f 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1442,8 +1442,6 @@ void absorb_git_dir_into_superproject(const char *prefix,
 
 	/* Not populated? */
 	if (!sub_git_dir) {
-		char *real_new_git_dir;
-		const char *new_git_dir;
 		const struct submodule *sub;
 
 		if (err_code == READ_GITFILE_ERR_STAT_FAILED) {
@@ -1466,13 +1464,8 @@ void absorb_git_dir_into_superproject(const char *prefix,
 		sub = submodule_from_path(null_sha1, path);
 		if (!sub)
 			die(_("could not lookup name for submodule '%s'"), path);
-		new_git_dir = git_path("modules/%s", sub->name);
-		if (safe_create_leading_directories_const(new_git_dir) < 0)
-			die(_("could not create directory '%s'"), new_git_dir);
-		real_new_git_dir = real_pathdup(new_git_dir);
-		connect_work_tree_and_git_dir(path, real_new_git_dir);
-
-		free(real_new_git_dir);
+		connect_work_tree_and_git_dir(path,
+			git_path("modules/%s", sub->name));
 	} else {
 		/* Is it already absorbed into the superprojects git dir? */
 		char *real_sub_git_dir = real_pathdup(sub_git_dir);
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 08/18] update submodules: add submodule config parsing

[Stefan Beller]

Similar to b33a15b08 (push: add recurseSubmodules config option,
2015-11-17) and 027771fcb1 (submodule: allow erroneous values for the
fetchRecurseSubmodules option, 2015-08-17), we add submodule-config code
that is later used to parse whether we are interested in updating
submodules.

We need the `die_on_error` parameter to be able to call this parsing
function for the config file as well, which if incorrect lets Git die.

As we're just touching the header file, also mark all functions extern.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule-config.c | 20 ++++++++++++++++++++
 submodule-config.h | 17 +++++++++--------
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/submodule-config.c b/submodule-config.c
index 93453909cf..3e8e380d98 100644
--- a/submodule-config.c
+++ b/submodule-config.c
@@ -234,6 +234,26 @@ int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg)
 	return parse_fetch_recurse(opt, arg, 1);
 }
 
+static int parse_update_recurse(const char *opt, const char *arg,
+				int die_on_error)
+{
+	switch (git_config_maybe_bool(opt, arg)) {
+	case 1:
+		return RECURSE_SUBMODULES_ON;
+	case 0:
+		return RECURSE_SUBMODULES_OFF;
+	default:
+		if (die_on_error)
+			die("bad %s argument: %s", opt, arg);
+		return RECURSE_SUBMODULES_ERROR;
+	}
+}
+
+int parse_update_recurse_submodules_arg(const char *opt, const char *arg)
+{
+	return parse_update_recurse(opt, arg, 1);
+}
+
 static int parse_push_recurse(const char *opt, const char *arg,
 			       int die_on_error)
 {
diff --git a/submodule-config.h b/submodule-config.h
index 70f19363fd..d434ecdb45 100644
--- a/submodule-config.h
+++ b/submodule-config.h
@@ -22,16 +22,17 @@ struct submodule {
 	int recommend_shallow;
 };
 
-int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg);
-int parse_push_recurse_submodules_arg(const char *opt, const char *arg);
-int parse_submodule_config_option(const char *var, const char *value);
-const struct submodule *submodule_from_name(const unsigned char *commit_or_tree,
-		const char *name);
-const struct submodule *submodule_from_path(const unsigned char *commit_or_tree,
-		const char *path);
+extern int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_update_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_push_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_submodule_config_option(const char *var, const char *value);
+extern const struct submodule *submodule_from_name(
+		const unsigned char *commit_or_tree, const char *name);
+extern const struct submodule *submodule_from_path(
+		const unsigned char *commit_or_tree, const char *path);
 extern int gitmodule_sha1_from_commit(const unsigned char *commit_sha1,
 				      unsigned char *gitmodules_sha1,
 				      struct strbuf *rev);
-void submodule_free(void);
+extern void submodule_free(void);
 
 #endif /* SUBMODULE_CONFIG_H */
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 09/18] update submodules: add a config option to determine if submodules are updated

[Stefan Beller]

In later patches we introduce the options and flag for commands
that modify the working directory, e.g. git-checkout.

Have a central place to store such settings whether we want to update
a submodule.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 6 ++++++
 submodule.h | 1 +
 2 files changed, 7 insertions(+)

diff --git a/submodule.c b/submodule.c
index 04d185738f..591f4a694e 100644
--- a/submodule.c
+++ b/submodule.c
@@ -17,6 +17,7 @@
 #include "worktree.h"
 
 static int config_fetch_recurse_submodules = RECURSE_SUBMODULES_ON_DEMAND;
+static int config_update_recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 static int parallel_jobs = 1;
 static struct string_list changed_submodule_paths = STRING_LIST_INIT_NODUP;
 static int initialized_fetch_ref_tips;
@@ -542,6 +543,11 @@ void set_config_fetch_recurse_submodules(int value)
 	config_fetch_recurse_submodules = value;
 }
 
+void set_config_update_recurse_submodules(int value)
+{
+	config_update_recurse_submodules = value;
+}
+
 static int has_remote(const char *refname, const struct object_id *oid,
 		      int flags, void *cb_data)
 {
diff --git a/submodule.h b/submodule.h
index 0b915bd3ac..b4e60c08d2 100644
--- a/submodule.h
+++ b/submodule.h
@@ -64,6 +64,7 @@ extern void show_submodule_inline_diff(FILE *f, const char *path,
 		const char *del, const char *add, const char *reset,
 		const struct diff_options *opt);
 extern void set_config_fetch_recurse_submodules(int value);
+extern void set_config_update_recurse_submodules(int value);
 extern void check_for_new_submodule_commits(unsigned char new_sha1[20]);
 extern int fetch_populated_submodules(const struct argv_array *options,
 			       const char *prefix, int command_line_option,
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 10/18] submodules: introduce check to see whether to touch a submodule

[Stefan Beller]

In later patches we introduce the --recurse-submodule flag for commands
that modify the working directory, e.g. git-checkout.

It is potentially expensive to check if a submodule needs an update,
because a common theme to interact with submodules is to spawn a child
process for each interaction.

So let's introduce a function that checks if a submodule needs
to be checked for an update before attempting the update.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 16 ++++++++++++++++
 submodule.h |  7 +++++++
 2 files changed, 23 insertions(+)

diff --git a/submodule.c b/submodule.c
index 591f4a694e..8b2c0212be 100644
--- a/submodule.c
+++ b/submodule.c
@@ -548,6 +548,22 @@ void set_config_update_recurse_submodules(int value)
 	config_update_recurse_submodules = value;
 }
 
+int should_update_submodules(void)
+{
+	return config_update_recurse_submodules == RECURSE_SUBMODULES_ON;
+}
+
+const struct submodule *submodule_from_ce(const struct cache_entry *ce)
+{
+	if (!S_ISGITLINK(ce->ce_mode))
+		return NULL;
+
+	if (!should_update_submodules())
+		return NULL;
+
+	return submodule_from_path(null_sha1, ce->name);
+}
+
 static int has_remote(const char *refname, const struct object_id *oid,
 		      int flags, void *cb_data)
 {
diff --git a/submodule.h b/submodule.h
index b4e60c08d2..6f3fe85c7c 100644
--- a/submodule.h
+++ b/submodule.h
@@ -65,6 +65,13 @@ extern void show_submodule_inline_diff(FILE *f, const char *path,
 		const struct diff_options *opt);
 extern void set_config_fetch_recurse_submodules(int value);
 extern void set_config_update_recurse_submodules(int value);
+/* Check if we want to update any submodule.*/
+extern int should_update_submodules(void);
+/*
+ * Returns the submodule struct if the given ce entry is a submodule
+ * and it should be updated. Returns NULL otherwise.
+ */
+extern const struct submodule *submodule_from_ce(const struct cache_entry *ce);
 extern void check_for_new_submodule_commits(unsigned char new_sha1[20]);
 extern int fetch_populated_submodules(const struct argv_array *options,
 			       const char *prefix, int command_line_option,
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 11/18] update submodules: move up prepare_submodule_repo_env

[Stefan Beller]

In a later patch we need to prepare the submodule environment with
another git directory, so split up the function.

Also move it up in the file such that we do not need to declare the
function later before using it.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/submodule.c b/submodule.c
index 8b2c0212be..0b2596e88a 100644
--- a/submodule.c
+++ b/submodule.c
@@ -356,6 +356,23 @@ static void print_submodule_summary(struct rev_info *rev, FILE *f,
 	strbuf_release(&sb);
 }
 
+static void prepare_submodule_repo_env_no_git_dir(struct argv_array *out)
+{
+	const char * const *var;
+
+	for (var = local_repo_env; *var; var++) {
+		if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
+			argv_array_push(out, *var);
+	}
+}
+
+void prepare_submodule_repo_env(struct argv_array *out)
+{
+	prepare_submodule_repo_env_no_git_dir(out);
+	argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
+			 DEFAULT_GIT_DIR_ENVIRONMENT);
+}
+
 /* Helper function to display the submodule header line prior to the full
  * summary output. If it can locate the submodule objects directory it will
  * attempt to lookup both the left and right commits and put them into the
@@ -1390,18 +1407,6 @@ int parallel_submodules(void)
 	return parallel_jobs;
 }
 
-void prepare_submodule_repo_env(struct argv_array *out)
-{
-	const char * const *var;
-
-	for (var = local_repo_env; *var; var++) {
-		if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
-			argv_array_push(out, *var);
-	}
-	argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
-			 DEFAULT_GIT_DIR_ENVIRONMENT);
-}
-
 /*
  * Embeds a single submodules git directory into the superprojects git dir,
  * non recursively.
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 12/18] update submodules: add submodule_move_head

[Stefan Beller]

In later patches we introduce the options and flag for commands
that modify the working directory, e.g. git-checkout.

This piece of code will be used universally for
all these working tree modifications as it
* supports dry run to answer the question:
  "Is it safe to change the submodule to this new state?"
  e.g. is it overwriting untracked files or are there local
  changes that would be overwritten?
* supports a force flag that can be used for resetting
  the tree.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 submodule.h |   7 ++++
 2 files changed, 142 insertions(+)

diff --git a/submodule.c b/submodule.c
index 0b2596e88a..bc5fecf8c5 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1239,6 +1239,141 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
 	return ret;
 }
 
+static int submodule_has_dirty_index(const struct submodule *sub)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	argv_array_pushl(&cp.args, "diff-index", "--quiet", \
+					"--cached", "HEAD", NULL);
+	cp.no_stdin = 1;
+	cp.no_stdout = 1;
+	cp.dir = sub->path;
+	if (start_command(&cp))
+		die("could not recurse into submodule '%s'", sub->path);
+
+	return finish_command(&cp);
+}
+
+static void submodule_reset_index(const char *path)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.dir = path;
+
+	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
+	argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
+
+	argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);
+
+	if (run_command(&cp))
+		die("could not reset submodule index");
+}
+
+/**
+ * Moves a submodule at a given path from a given head to another new head.
+ * For edge cases (a submodule coming into existence or removing a submodule)
+ * pass NULL for old or new respectively.
+ */
+int submodule_move_head(const char *path,
+			 const char *old,
+			 const char *new,
+			 unsigned flags)
+{
+	int ret = 0;
+	struct child_process cp = CHILD_PROCESS_INIT;
+	const struct submodule *sub;
+
+	sub = submodule_from_path(null_sha1, path);
+
+	if (!sub)
+		die("BUG: could not get submodule information for '%s'", path);
+
+	if (old && !(flags & SUBMODULE_MOVE_HEAD_FORCE)) {
+		/* Check if the submodule has a dirty index. */
+		if (submodule_has_dirty_index(sub))
+			return error(_("submodule '%s' has dirty index"), path);
+	}
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
+		if (old) {
+			if (!submodule_uses_gitfile(path))
+				absorb_git_dir_into_superproject("", path,
+					ABSORB_GITDIR_RECURSE_SUBMODULES);
+		} else {
+			struct strbuf sb = STRBUF_INIT;
+			strbuf_addf(&sb, "%s/modules/%s",
+				    get_git_common_dir(), sub->name);
+			connect_work_tree_and_git_dir(path, sb.buf);
+			strbuf_release(&sb);
+
+			/* make sure the index is clean as well */
+			submodule_reset_index(path);
+		}
+	}
+
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.dir = path;
+
+	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
+	argv_array_pushl(&cp.args, "read-tree", NULL);
+
+	if (flags & SUBMODULE_MOVE_HEAD_DRY_RUN)
+		argv_array_push(&cp.args, "-n");
+	else
+		argv_array_push(&cp.args, "-u");
+
+	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
+		argv_array_push(&cp.args, "--reset");
+	else
+		argv_array_push(&cp.args, "-m");
+
+	argv_array_push(&cp.args, old ? old : EMPTY_TREE_SHA1_HEX);
+	argv_array_push(&cp.args, new ? new : EMPTY_TREE_SHA1_HEX);
+
+	if (run_command(&cp)) {
+		ret = -1;
+		goto out;
+	}
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
+		if (new) {
+			struct child_process cp1 = CHILD_PROCESS_INIT;
+			/* also set the HEAD accordingly */
+			cp1.git_cmd = 1;
+			cp1.no_stdin = 1;
+			cp1.dir = path;
+
+			argv_array_pushl(&cp1.args, "update-ref", "HEAD",
+					 new ? new : EMPTY_TREE_SHA1_HEX, NULL);
+
+			if (run_command(&cp1)) {
+				ret = -1;
+				goto out;
+			}
+		} else {
+			struct strbuf sb = STRBUF_INIT;
+
+			strbuf_addf(&sb, "%s/.git", path);
+			unlink_or_warn(sb.buf);
+			strbuf_release(&sb);
+
+			if (is_empty_dir(path))
+				rmdir_or_warn(path);
+		}
+	}
+out:
+	return ret;
+}
+
 static int find_first_merges(struct object_array *result, const char *path,
 		struct commit *a, struct commit *b)
 {
diff --git a/submodule.h b/submodule.h
index 6f3fe85c7c..4cdf6445f7 100644
--- a/submodule.h
+++ b/submodule.h
@@ -96,6 +96,13 @@ extern int push_unpushed_submodules(struct sha1_array *commits,
 extern void connect_work_tree_and_git_dir(const char *work_tree, const char *git_dir);
 extern int parallel_submodules(void);
 
+#define SUBMODULE_MOVE_HEAD_DRY_RUN (1<<0)
+#define SUBMODULE_MOVE_HEAD_FORCE   (1<<1)
+extern int submodule_move_head(const char *path,
+			       const char *old,
+			       const char *new,
+			       unsigned flags);
+
 /*
  * Prepare the "env_array" parameter of a "struct child_process" for executing
  * a submodule by clearing any repo-specific envirionment variables, but
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 13/18] unpack-trees: pass old oid to verify_clean_submodule

[Stefan Beller]

The check (which uses the old oid) is yet to be implemented, but this part
is just a refactor, so it can go separately first.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 unpack-trees.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 3a8ee19fe8..616a0ae4b2 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1407,7 +1407,8 @@ static void invalidate_ce_path(const struct cache_entry *ce,
  * Currently, git does not checkout subprojects during a superproject
  * checkout, so it is not going to overwrite anything.
  */
-static int verify_clean_submodule(const struct cache_entry *ce,
+static int verify_clean_submodule(const char *old_sha1,
+				  const struct cache_entry *ce,
 				  enum unpack_trees_error_types error_type,
 				  struct unpack_trees_options *o)
 {
@@ -1427,16 +1428,18 @@ static int verify_clean_subdirectory(const struct cache_entry *ce,
 	struct dir_struct d;
 	char *pathbuf;
 	int cnt = 0;
-	unsigned char sha1[20];
 
-	if (S_ISGITLINK(ce->ce_mode) &&
-	    resolve_gitlink_ref(ce->name, "HEAD", sha1) == 0) {
-		/* If we are not going to update the submodule, then
+	if (S_ISGITLINK(ce->ce_mode)) {
+		unsigned char sha1[20];
+		int sub_head = resolve_gitlink_ref(ce->name, "HEAD", sha1);
+		/*
+		 * If we are not going to update the submodule, then
 		 * we don't care.
 		 */
-		if (!hashcmp(sha1, ce->oid.hash))
+		if (!sub_head && !hashcmp(sha1, ce->oid.hash))
 			return 0;
-		return verify_clean_submodule(ce, error_type, o);
+		return verify_clean_submodule(sub_head ? NULL : sha1_to_hex(sha1),
+					      ce, error_type, o);
 	}
 
 	/*
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 14/18] unpack-trees: check if we can perform the operation for submodules

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 unpack-trees.c | 131 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
 unpack-trees.h |   1 +
 2 files changed, 123 insertions(+), 9 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 616a0ae4b2..8333da2cc9 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -10,6 +10,8 @@
 #include "attr.h"
 #include "split-index.h"
 #include "dir.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 /*
  * Error messages expected by scripts out of plumbing commands such as
@@ -45,6 +47,9 @@ static const char *unpack_plumbing_errors[NB_UNPACK_TREES_ERROR_TYPES] = {
 
 	/* ERROR_WOULD_LOSE_ORPHANED_REMOVED */
 	"Working tree file '%s' would be removed by sparse checkout update.",
+
+	/* ERROR_WOULD_LOSE_SUBMODULE */
+	"Submodule '%s' cannot checkout new HEAD.",
 };
 
 #define ERRORMSG(o,type) \
@@ -161,6 +166,8 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 		_("The following working tree files would be overwritten by sparse checkout update:\n%s");
 	msgs[ERROR_WOULD_LOSE_ORPHANED_REMOVED] =
 		_("The following working tree files would be removed by sparse checkout update:\n%s");
+	msgs[ERROR_WOULD_LOSE_SUBMODULE] =
+		_("Submodule '%s' cannot checkout new HEAD");
 
 	opts->show_all_errors = 1;
 	/* rejected paths may not have a static buffer */
@@ -240,12 +247,75 @@ static void display_error_msgs(struct unpack_trees_options *o)
 		fprintf(stderr, _("Aborting\n"));
 }
 
+static int check_submodule_move_head(const struct cache_entry *ce,
+				     const char *old_id,
+				     const char *new_id,
+				     struct unpack_trees_options *o)
+{
+	const struct submodule *sub = submodule_from_ce(ce);
+	if (!sub)
+		return 0;
+
+	switch (sub->update_strategy.type) {
+	case SM_UPDATE_UNSPECIFIED:
+	case SM_UPDATE_CHECKOUT:
+		if (submodule_move_head(ce->name, old_id, new_id, SUBMODULE_MOVE_HEAD_DRY_RUN))
+			return o->gently ? -1 :
+				add_rejected_path(o, ERROR_WOULD_LOSE_SUBMODULE, ce->name);
+		return 0;
+	case SM_UPDATE_NONE:
+		return 0;
+	case SM_UPDATE_REBASE:
+	case SM_UPDATE_MERGE:
+	case SM_UPDATE_COMMAND:
+	default:
+		warning(_("submodule update strategy not supported for submodule '%s'"), ce->name);
+		return -1;
+	}
+}
+
+static void reload_gitmodules_file(struct index_state *index,
+				   struct checkout *state)
+{
+	int i;
+	for (i = 0; i < index->cache_nr; i++) {
+		struct cache_entry *ce = index->cache[i];
+		if (ce->ce_flags & CE_UPDATE) {
+			int r = strcmp(ce->name, ".gitmodules");
+			if (r < 0)
+				continue;
+			else if (r == 0) {
+				submodule_free();
+				checkout_entry(ce, state, NULL);
+				gitmodules_config();
+				git_config(submodule_config, NULL);
+			} else
+				break;
+		}
+	}
+}
+
 /*
  * Unlink the last component and schedule the leading directories for
  * removal, such that empty directories get removed.
  */
 static void unlink_entry(const struct cache_entry *ce)
 {
+	const struct submodule *sub = submodule_from_ce(ce);
+	if (sub) {
+		switch (sub->update_strategy.type) {
+		case SM_UPDATE_UNSPECIFIED:
+		case SM_UPDATE_CHECKOUT:
+		case SM_UPDATE_REBASE:
+		case SM_UPDATE_MERGE:
+			submodule_move_head(ce->name, "HEAD", NULL,
+					    SUBMODULE_MOVE_HEAD_FORCE);
+			break;
+		case SM_UPDATE_NONE:
+		case SM_UPDATE_COMMAND:
+			return; /* Do not touch the submodule. */
+		}
+	}
 	if (!check_leading_path(ce->name, ce_namelen(ce)))
 		return;
 	if (remove_or_warn(ce->ce_mode, ce->name))
@@ -301,6 +371,9 @@ static int check_updates(struct unpack_trees_options *o)
 	remove_marked_cache_entries(index);
 	remove_scheduled_dirs();
 
+	if (should_update_submodules() && o->update && !o->dry_run)
+		reload_gitmodules_file(index, &state);
+
 	for (i = 0; i < index->cache_nr; i++) {
 		struct cache_entry *ce = index->cache[i];
 
@@ -1358,17 +1431,26 @@ static int verify_uptodate_1(const struct cache_entry *ce,
 	if (!lstat(ce->name, &st)) {
 		int flags = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE;
 		unsigned changed = ie_match_stat(o->src_index, ce, &st, flags);
+
+		if (submodule_from_ce(ce)) {
+			int r = check_submodule_move_head(ce,
+				"HEAD", oid_to_hex(&ce->oid), o);
+			if (r)
+				return o->gently ? -1 :
+					add_rejected_path(o, error_type, ce->name);
+			return 0;
+		}
+
 		if (!changed)
 			return 0;
 		/*
-		 * NEEDSWORK: the current default policy is to allow
-		 * submodule to be out of sync wrt the superproject
-		 * index.  This needs to be tightened later for
-		 * submodules that are marked to be automatically
-		 * checked out.
+		 * Historic default policy was to allow submodule to be out
+		 * of sync wrt the superproject index. If the submodule was
+		 * not considered interesting above, we don't care here.
 		 */
 		if (S_ISGITLINK(ce->ce_mode))
 			return 0;
+
 		errno = 0;
 	}
 	if (errno == ENOENT)
@@ -1412,7 +1494,11 @@ static int verify_clean_submodule(const char *old_sha1,
 				  enum unpack_trees_error_types error_type,
 				  struct unpack_trees_options *o)
 {
-	return 0;
+	if (!submodule_from_ce(ce))
+		return 0;
+
+	return check_submodule_move_head(ce, old_sha1,
+					 oid_to_hex(&ce->oid), o);
 }
 
 static int verify_clean_subdirectory(const struct cache_entry *ce,
@@ -1578,9 +1664,15 @@ static int verify_absent_1(const struct cache_entry *ce,
 		path = xmemdupz(ce->name, len);
 		if (lstat(path, &st))
 			ret = error_errno("cannot stat '%s'", path);
-		else
-			ret = check_ok_to_remove(path, len, DT_UNKNOWN, NULL,
-						 &st, error_type, o);
+		else {
+			if (submodule_from_ce(ce))
+				ret = check_submodule_move_head(ce,
+								oid_to_hex(&ce->oid),
+								NULL, o);
+			else
+				ret = check_ok_to_remove(path, len, DT_UNKNOWN, NULL,
+							 &st, error_type, o);
+		}
 		free(path);
 		return ret;
 	} else if (lstat(ce->name, &st)) {
@@ -1588,6 +1680,10 @@ static int verify_absent_1(const struct cache_entry *ce,
 			return error_errno("cannot stat '%s'", ce->name);
 		return 0;
 	} else {
+		if (submodule_from_ce(ce))
+			return check_submodule_move_head(ce, oid_to_hex(&ce->oid),
+							 NULL, o);
+
 		return check_ok_to_remove(ce->name, ce_namelen(ce),
 					  ce_to_dtype(ce), ce, &st,
 					  error_type, o);
@@ -1643,6 +1739,15 @@ static int merged_entry(const struct cache_entry *ce,
 			return -1;
 		}
 		invalidate_ce_path(merge, o);
+
+		if (submodule_from_ce(ce)) {
+			int ret = check_submodule_move_head(ce, NULL,
+							    oid_to_hex(&ce->oid),
+							    o);
+			if (ret)
+				return ret;
+		}
+
 	} else if (!(old->ce_flags & CE_CONFLICTED)) {
 		/*
 		 * See if we can re-use the old CE directly?
@@ -1663,6 +1768,14 @@ static int merged_entry(const struct cache_entry *ce,
 			update |= old->ce_flags & (CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
 			invalidate_ce_path(old, o);
 		}
+
+		if (submodule_from_ce(ce)) {
+			int ret = check_submodule_move_head(ce, oid_to_hex(&old->oid),
+							    oid_to_hex(&ce->oid),
+							    o);
+			if (ret)
+				return ret;
+		}
 	} else {
 		/*
 		 * Previously unmerged entry left as an existence
diff --git a/unpack-trees.h b/unpack-trees.h
index 36a73a6d00..6c48117b84 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -21,6 +21,7 @@ enum unpack_trees_error_types {
 	ERROR_SPARSE_NOT_UPTODATE_FILE,
 	ERROR_WOULD_LOSE_ORPHANED_OVERWRITTEN,
 	ERROR_WOULD_LOSE_ORPHANED_REMOVED,
+	ERROR_WOULD_LOSE_SUBMODULE,
 	NB_UNPACK_TREES_ERROR_TYPES
 };
 
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 15/18] read-cache, remove_marked_cache_entries: wipe selected submodules.

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 read-cache.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/read-cache.c b/read-cache.c
index 9054369dd0..9a2abacf7a 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -18,6 +18,8 @@
 #include "varint.h"
 #include "split-index.h"
 #include "utf8.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -520,6 +522,22 @@ int remove_index_entry_at(struct index_state *istate, int pos)
 	return 1;
 }
 
+static void remove_submodule_according_to_strategy(const struct submodule *sub)
+{
+	switch (sub->update_strategy.type) {
+	case SM_UPDATE_UNSPECIFIED:
+	case SM_UPDATE_CHECKOUT:
+	case SM_UPDATE_REBASE:
+	case SM_UPDATE_MERGE:
+		submodule_move_head(sub->path, "HEAD", NULL, \
+				    SUBMODULE_MOVE_HEAD_FORCE);
+		break;
+	case SM_UPDATE_NONE:
+	case SM_UPDATE_COMMAND:
+		; /* Do not touch the submodule. */
+	}
+}
+
 /*
  * Remove all cache entries marked for removal, that is where
  * CE_REMOVE is set in ce_flags.  This is much more effective than
@@ -532,8 +550,13 @@ void remove_marked_cache_entries(struct index_state *istate)
 
 	for (i = j = 0; i < istate->cache_nr; i++) {
 		if (ce_array[i]->ce_flags & CE_REMOVE) {
-			remove_name_hash(istate, ce_array[i]);
-			save_or_free_index_entry(istate, ce_array[i]);
+			const struct submodule *sub = submodule_from_ce(ce_array[i]);
+			if (sub) {
+				remove_submodule_according_to_strategy(sub);
+			} else {
+				remove_name_hash(istate, ce_array[i]);
+				save_or_free_index_entry(istate, ce_array[i]);
+			}
 		}
 		else
 			ce_array[j++] = ce_array[i];
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 16/18] entry.c: update submodules when interesting

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 entry.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/entry.c b/entry.c
index c6eea240b6..d2b512da90 100644
--- a/entry.c
+++ b/entry.c
@@ -2,6 +2,7 @@
 #include "blob.h"
 #include "dir.h"
 #include "streaming.h"
+#include "submodule.h"
 
 static void create_directories(const char *path, int path_len,
 			       const struct checkout *state)
@@ -146,6 +147,7 @@ static int write_entry(struct cache_entry *ce,
 	unsigned long size;
 	size_t wrote, newsize = 0;
 	struct stat st;
+	const struct submodule *sub;
 
 	if (ce_mode_s_ifmt == S_IFREG) {
 		struct stream_filter *filter = get_stream_filter(ce->name,
@@ -203,6 +205,10 @@ static int write_entry(struct cache_entry *ce,
 			return error("cannot create temporary submodule %s", path);
 		if (mkdir(path, 0777) < 0)
 			return error("cannot create submodule directory %s", path);
+		sub = submodule_from_ce(ce);
+		if (sub)
+			return submodule_move_head(ce->name,
+				NULL, oid_to_hex(&ce->oid), SUBMODULE_MOVE_HEAD_FORCE);
 		break;
 	default:
 		return error("unknown file mode for %s in index", path);
@@ -259,7 +265,31 @@ int checkout_entry(struct cache_entry *ce,
 	strbuf_add(&path, ce->name, ce_namelen(ce));
 
 	if (!check_path(path.buf, path.len, &st, state->base_dir_len)) {
+		const struct submodule *sub;
 		unsigned changed = ce_match_stat(ce, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
+		/*
+		 * Needs to be checked before !changed returns early,
+		 * as the possibly empty directory was not changed
+		 */
+		sub = submodule_from_ce(ce);
+		if (sub) {
+			int err;
+			if (!is_submodule_populated_gently(ce->name, &err)) {
+				struct stat sb;
+				if (lstat(ce->name, &sb))
+					die(_("could not stat file '%s'"), ce->name);
+				if (!(st.st_mode & S_IFDIR))
+					unlink_or_warn(ce->name);
+
+				return submodule_move_head(ce->name,
+					NULL, oid_to_hex(&ce->oid),
+					SUBMODULE_MOVE_HEAD_FORCE);
+			} else
+				return submodule_move_head(ce->name,
+					"HEAD", oid_to_hex(&ce->oid),
+					SUBMODULE_MOVE_HEAD_FORCE);
+		}
+
 		if (!changed)
 			return 0;
 		if (!state->force) {
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 17/18] builtin/checkout: add --recurse-submodules switch

[Stefan Beller]

This exposes a flag to recurse into submodules
in builtin/checkout making use of the code implemented
in prior patches.

A new failure mode is introduced in the submodule
update library, as the directory/submodule conflict
is not solved in prior patches.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/git-checkout.txt |  7 +++++++
 builtin/checkout.c             | 28 ++++++++++++++++++++++++++++
 t/lib-submodule-update.sh      | 23 +++++++++++++++++------
 t/t2013-checkout-submodule.sh  |  5 +++++
 4 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 8e2c0662dd..d6399c0af8 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -256,6 +256,13 @@ section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
 	out anyway. In other words, the ref can be held by more than one
 	worktree.
 
+--[no-]recurse-submodules::
+	Using --recurse-submodules will update the content of all initialized
+	submodules according to the commit recorded in the superproject. If
+	local modifications in a submodule would be overwritten the checkout
+	will fail unless `-f` is used. If nothing (or --no-recurse-submodules)
+	is used, the work trees of submodules will not be updated.
+
 <branch>::
 	Branch to checkout; if it refers to a branch (i.e., a name that,
 	when prepended with "refs/heads/", is a valid ref), then that
diff --git a/builtin/checkout.c b/builtin/checkout.c
index f174f50303..e9c5fcfaf8 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -21,12 +21,31 @@
 #include "submodule-config.h"
 #include "submodule.h"
 
+static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
+
 static const char * const checkout_usage[] = {
 	N_("git checkout [<options>] <branch>"),
 	N_("git checkout [<options>] [<branch>] -- <file>..."),
 	NULL,
 };
 
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
+{
+	if (unset) {
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
 struct checkout_opts {
 	int patch_mode;
 	int quiet;
@@ -1163,6 +1182,9 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 				N_("second guess 'git checkout <no-such-branch>'")),
 		OPT_BOOL(0, "ignore-other-worktrees", &opts.ignore_other_worktrees,
 			 N_("do not check if another worktree is holding the given ref")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules },
 		OPT_BOOL(0, "progress", &opts.show_progress, N_("force progress reporting")),
 		OPT_END(),
 	};
@@ -1193,6 +1215,12 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
 	}
 
+	if (recurse_submodules != RECURSE_SUBMODULES_OFF) {
+		git_config(submodule_config, NULL);
+		if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT)
+			set_config_update_recurse_submodules(recurse_submodules);
+	}
+
 	if ((!!opts.new_branch + !!opts.new_branch_force + !!opts.new_orphan_branch) > 1)
 		die(_("-b, -B and --orphan are mutually exclusive"));
 
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 5b885cfbf8..6a78139f90 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -782,6 +782,11 @@ test_submodule_forced_switch () {
 
 test_submodule_switch_recursing () {
 	command="$1"
+	RESULT=success
+	if test "$KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS" = 1
+	then
+		RESULT=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -891,7 +896,7 @@ test_submodule_switch_recursing () {
 	'
 	# Replacing a submodule with files in a directory must succeeds
 	# when the submodule is clean
-	test_expect_success "$command: replace submodule with a directory" '
+	test_expect_$RESULT "$command: replace submodule with a directory" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -903,7 +908,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... absorbing a .git directory.
-	test_expect_success "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
+	test_expect_$RESULT "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -931,7 +936,7 @@ test_submodule_switch_recursing () {
 	'
 
 	# ... must check its local work tree for untracked files
-	test_expect_success "$command: replace submodule with a file must fail with untracked files" '
+	test_expect_$RESULT "$command: replace submodule with a file must fail with untracked files" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -987,7 +992,8 @@ test_submodule_switch_recursing () {
 		)
 	'
 
-	test_expect_success "$command: modified submodule updates submodule recursively" '
+	# recursing deeper than one level doesn't work yet.
+	test_expect_failure "$command: modified submodule updates submodule recursively" '
 		prolog &&
 		reset_work_tree_to_interested add_nested_sub &&
 		(
@@ -1006,6 +1012,11 @@ test_submodule_switch_recursing () {
 # the superproject as well as the submodule is allowed.
 test_submodule_forced_switch_recursing () {
 	command="$1"
+	RESULT=success
+	if test "$KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS" = 1
+	then
+		RESULT=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear creates empty dir ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -1100,7 +1111,7 @@ test_submodule_forced_switch_recursing () {
 		)
 	'
 	# Replacing a submodule with files in a directory ...
-	test_expect_success "$command: replace submodule with a directory" '
+	test_expect_$RESULT "$command: replace submodule with a directory" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -1151,7 +1162,7 @@ test_submodule_forced_switch_recursing () {
 	'
 
 	# ... but stops for untracked files that would be lost
-	test_expect_success "$command: replace submodule with a file" '
+	test_expect_$RESULT "$command: replace submodule with a file stops for untracked files" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
diff --git a/t/t2013-checkout-submodule.sh b/t/t2013-checkout-submodule.sh
index 6847f75822..aa35223369 100755
--- a/t/t2013-checkout-submodule.sh
+++ b/t/t2013-checkout-submodule.sh
@@ -63,6 +63,11 @@ test_expect_success '"checkout <submodule>" honors submodule.*.ignore from .git/
 	! test -s actual
 '
 
+KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+test_submodule_switch_recursing "git checkout --recurse-submodules"
+
+test_submodule_forced_switch_recursing "git checkout -f --recurse-submodules"
+
 test_submodule_switch "git checkout"
 
 test_submodule_forced_switch "git checkout -f"
-- 
2.12.0.rc1.52.ge239d7e709.dirty

[PATCH 18/18] builtin/read-tree: add --recurse-submodules switch

[Stefan Beller]

A new known failure mode is introduced[1], which is actually not
a failure but a feature in read-tree. Unlike checkout for which
the recursive submodule tests were originally written, read-tree does
warn about ignored untracked files that would be overwritten.
For the sake of keeping the test library for submodules genric, just
mark the test as a failure.

[1] KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/git-read-tree.txt |  6 ++++++
 builtin/read-tree.c             | 29 +++++++++++++++++++++++++++++
 t/lib-submodule-update.sh       |  7 ++++++-
 t/t1013-read-tree-submodule.sh  |  7 +++++++
 4 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt
index fa1d557e5b..ed9d63ef4a 100644
--- a/Documentation/git-read-tree.txt
+++ b/Documentation/git-read-tree.txt
@@ -115,6 +115,12 @@ OPTIONS
 	directories the index file and index output file are
 	located in.
 
+--[no-]recurse-submodules::
+	Using --recurse-submodules will update the content of all initialized
+	submodules according to the commit recorded in the superproject by
+	calling read-tree recursively, also setting the submodules HEAD to be
+	detached at that commit.
+
 --no-sparse-checkout::
 	Disable sparse checkout support even if `core.sparseCheckout`
 	is true.
diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 8ba64bc785..2dc5cc06da 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -15,10 +15,13 @@
 #include "builtin.h"
 #include "parse-options.h"
 #include "resolve-undo.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 static int nr_trees;
 static int read_empty;
 static struct tree *trees[MAX_UNPACK_TREES];
+int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 
 static int list_tree(unsigned char *sha1)
 {
@@ -96,6 +99,23 @@ static int debug_merge(const struct cache_entry * const *stages,
 	return 0;
 }
 
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
+{
+	if (unset) {
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
 static struct lock_file lock_file;
 
 int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
@@ -137,6 +157,9 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 			 N_("skip applying sparse checkout filter")),
 		OPT_BOOL(0, "debug-unpack", &opts.debug_unpack,
 			 N_("debug unpack-trees")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules },
 		OPT_END()
 	};
 
@@ -152,6 +175,12 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 
 	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
 
+	if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT) {
+		gitmodules_config();
+		git_config(submodule_config, NULL);
+		set_config_update_recurse_submodules(RECURSE_SUBMODULES_ON);
+	}
+
 	prefix_set = opts.prefix ? 1 : 0;
 	if (1 < opts.merge + opts.reset + prefix_set)
 		die("Which one? -m, --reset, or --prefix?");
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 6a78139f90..949ebd546c 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -787,6 +787,11 @@ test_submodule_switch_recursing () {
 	then
 		RESULT=failure
 	fi
+	RESULT1=success
+	if test "$KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED" = 1
+	then
+		RESULT1=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -827,7 +832,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... but an ignored file is fine.
-	test_expect_success "$command: added submodule removes an untracked ignored file" '
+	test_expect_$RESULT1 "$command: added submodule removes an untracked ignored file" '
 		test_when_finished "rm submodule_update/.git/info/exclude" &&
 		prolog &&
 		reset_work_tree_to_interested no_submodule &&
diff --git a/t/t1013-read-tree-submodule.sh b/t/t1013-read-tree-submodule.sh
index 20526aed34..7019d0a04f 100755
--- a/t/t1013-read-tree-submodule.sh
+++ b/t/t1013-read-tree-submodule.sh
@@ -5,6 +5,13 @@ test_description='read-tree can handle submodules'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-submodule-update.sh
 
+KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED=1
+
+test_submodule_switch_recursing "git read-tree --recurse-submodules -u -m"
+
+test_submodule_forced_switch_recursing "git read-tree --recurse-submodules -u --reset"
+
 test_submodule_switch "git read-tree -u -m"
 
 test_submodule_forced_switch "git read-tree -u --reset"
-- 
2.12.0.rc1.52.ge239d7e709.dirty

Re: [PATCH 03/18] lib-submodule-update: teach test_submodule_content the -C <dir> flag

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> Signed-off-by: Stefan Beller <sbeller@google.com>
> ---
>  t/lib-submodule-update.sh | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
> index c0d6325133..00128f28b5 100755
> --- a/t/lib-submodule-update.sh
> +++ b/t/lib-submodule-update.sh
> @@ -193,6 +193,11 @@ test_superproject_content () {
>  # Test that the given submodule at path "$1" contains the content according
>  # to the submodule commit recorded in the superproject's commit "$2"
>  test_submodule_content () {
> +	if test x"$1" = "x-C"
> +	then
> +		cd "$2"
> +		shift; shift;

That's old fashoned like me ;-)  

It seems "shift [<n>]" is already used elsewhere in our test scripts
without getting complaints.

'git-difftool-helper.sh' is the only one that uses number above 1 in
the scripted Porcelains, so it is possible that an esoteric platform
without a shell that understands it may be built and used _without_
passing our test suite, so I'd be wary of using it in the scripted
Porcelains, but this is part of the test suite, so I would think it
is OK.

> +	fi
>  	if test $# != 2
>  	then
>  		echo "test_submodule_content needs two arguments"

Re: [PATCH 05/18] lib-submodule-update.sh: define tests for recursing into submodules

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> +	# ... and ignored files are ignroed

ignored.

Re: [PATCH 16/18] entry.c: update submodules when interesting

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> Signed-off-by: Stefan Beller <sbeller@google.com>
> ---
>  entry.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
>
> diff --git a/entry.c b/entry.c
> index c6eea240b6..d2b512da90 100644
> --- a/entry.c
> +++ b/entry.c
> @@ -2,6 +2,7 @@
>  #include "blob.h"
>  #include "dir.h"
>  #include "streaming.h"
> +#include "submodule.h"
>  
>  static void create_directories(const char *path, int path_len,
>  			       const struct checkout *state)
> @@ -146,6 +147,7 @@ static int write_entry(struct cache_entry *ce,
>  	unsigned long size;
>  	size_t wrote, newsize = 0;
>  	struct stat st;
> +	const struct submodule *sub;
>  
>  	if (ce_mode_s_ifmt == S_IFREG) {
>  		struct stream_filter *filter = get_stream_filter(ce->name,
> @@ -203,6 +205,10 @@ static int write_entry(struct cache_entry *ce,
>  			return error("cannot create temporary submodule %s", path);
>  		if (mkdir(path, 0777) < 0)
>  			return error("cannot create submodule directory %s", path);
> +		sub = submodule_from_ce(ce);
> +		if (sub)
> +			return submodule_move_head(ce->name,
> +				NULL, oid_to_hex(&ce->oid), SUBMODULE_MOVE_HEAD_FORCE);
>  		break;
>  	default:
>  		return error("unknown file mode for %s in index", path);
> @@ -259,7 +265,31 @@ int checkout_entry(struct cache_entry *ce,
>  	strbuf_add(&path, ce->name, ce_namelen(ce));
>  
>  	if (!check_path(path.buf, path.len, &st, state->base_dir_len)) {
> +		const struct submodule *sub;
>  		unsigned changed = ce_match_stat(ce, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
> +		/*
> +		 * Needs to be checked before !changed returns early,
> +		 * as the possibly empty directory was not changed
> +		 */
> +		sub = submodule_from_ce(ce);
> +		if (sub) {
> +			int err;
> +			if (!is_submodule_populated_gently(ce->name, &err)) {
> +				struct stat sb;
> +				if (lstat(ce->name, &sb))
> +					die(_("could not stat file '%s'"), ce->name);
> +				if (!(st.st_mode & S_IFDIR))
> +					unlink_or_warn(ce->name);

We found that the path ce->name is supposed to be a submodule that
is checked out, we found that the submodule is not yet populated, we
tried to make sure what is on that path, and its failure would cause
us to die().  All that is sensible.

Then we want to make sure the filesystem entity at the path
currently is a directory and otherwise unlink (i.e. we may have an
unrelated file that is not tracked there, or perhaps the user earlier
decided that replacing the submodule with a single file is a good
idea, but then getting rid of the change with "checkout -f" before
doing "git add" on that file).  That is also sensible.

But if that unlink fails, shouldn't we die, just like the case where
we cannot tell what is at the path ce->name?

And if that unlink succeeds, instead of having an empty directory,
we start the "move-head" call to switch from NULL to ce->oid without
having any directory.  Wouldn't we want to mkdir() here (and remove
mkdir() in submodule_move_head() if there is one---if there isn't
then I do not think this codepath would work)?

If we had a directory here, but if that directory is not empty,
should we proceed?  I am assuming (I haven't carefully read
"move-head") that it is OK because the "run an equivalent of
'checkout --detach ce->oid'" done by "move-head" would notice a
possible information loss to overwrite an untracked path (everything
is "untracked" as the head moves from NULL to ce->oid in this case),
and prevent it from happening.

Am I reading the design correctly?

> +				return submodule_move_head(ce->name,
> +					NULL, oid_to_hex(&ce->oid),
> +					SUBMODULE_MOVE_HEAD_FORCE);
> +			} else
> +				return submodule_move_head(ce->name,
> +					"HEAD", oid_to_hex(&ce->oid),
> +					SUBMODULE_MOVE_HEAD_FORCE);
> +		}
> +
>  		if (!changed)
>  			return 0;
>  		if (!state->force) {

Re: [PATCH 18/18] builtin/read-tree: add --recurse-submodules switch

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> A new known failure mode is introduced[1], which is actually not
> a failure but a feature in read-tree. Unlike checkout for which
> the recursive submodule tests were originally written, read-tree does
> warn about ignored untracked files that would be overwritten.
> For the sake of keeping the test library for submodules genric, just

generic

Re: [PATCH 15/18] read-cache, remove_marked_cache_entries: wipe selected submodules.

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> Signed-off-by: Stefan Beller <sbeller@google.com>
> ---
>  read-cache.c | 27 +++++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/read-cache.c b/read-cache.c
> index 9054369dd0..9a2abacf7a 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -18,6 +18,8 @@
>  #include "varint.h"
>  #include "split-index.h"
>  #include "utf8.h"
> +#include "submodule.h"
> +#include "submodule-config.h"
>  
>  /* Mask for the name length in ce_flags in the on-disk index */
>  
> @@ -520,6 +522,22 @@ int remove_index_entry_at(struct index_state *istate, int pos)
>  	return 1;
>  }
>  
> +static void remove_submodule_according_to_strategy(const struct submodule *sub)
> +{
> +	switch (sub->update_strategy.type) {
> +	case SM_UPDATE_UNSPECIFIED:
> +	case SM_UPDATE_CHECKOUT:
> +	case SM_UPDATE_REBASE:
> +	case SM_UPDATE_MERGE:
> +		submodule_move_head(sub->path, "HEAD", NULL, \

What is this backslash doing here?

> +				    SUBMODULE_MOVE_HEAD_FORCE);
> +		break;
> +	case SM_UPDATE_NONE:
> +	case SM_UPDATE_COMMAND:
> +		; /* Do not touch the submodule. */
> +	}
> +}
> +
>  /*
>   * Remove all cache entries marked for removal, that is where
>   * CE_REMOVE is set in ce_flags.  This is much more effective than
> @@ -532,8 +550,13 @@ void remove_marked_cache_entries(struct index_state *istate)
>  
>  	for (i = j = 0; i < istate->cache_nr; i++) {
>  		if (ce_array[i]->ce_flags & CE_REMOVE) {
> -			remove_name_hash(istate, ce_array[i]);
> -			save_or_free_index_entry(istate, ce_array[i]);
> +			const struct submodule *sub = submodule_from_ce(ce_array[i]);
> +			if (sub) {
> +				remove_submodule_according_to_strategy(sub);
> +			} else {
> +				remove_name_hash(istate, ce_array[i]);
> +				save_or_free_index_entry(istate, ce_array[i]);
> +			}

I cannot readily tell as the proposed log message is on the sketchy
side to explain the reasoning behind this, but this behaviour change
is done unconditionally (in other words, without introducing a flag
that is set by --recurse-submodules command line flag and switches
behaviour based on the flag) here.  What is the end-user visible
effect with this change?  Can we have a new test in this same patch
to demonstrate the desired behaviour introduced by this change (or
the bug this change fixes)?

>  		}
>  		else
>  			ce_array[j++] = ce_array[i];

Re: [PATCH 16/18] entry.c: update submodules when interesting

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

>> +			if (!is_submodule_populated_gently(ce->name, &err)) {
>> +				struct stat sb;
>> +				if (lstat(ce->name, &sb))
>> +					die(_("could not stat file '%s'"), ce->name);
>> +				if (!(st.st_mode & S_IFDIR))
>> +					unlink_or_warn(ce->name);
>
> We found that the path ce->name is supposed to be a submodule that
> is checked out, we found that the submodule is not yet populated, we
> tried to make sure what is on that path, and its failure would cause
> us to die().  All that is sensible.
> ...
> But if that unlink fails, shouldn't we die, just like the case where
> we cannot tell what is at the path ce->name?
>
> And if that unlink succeeds, instead of having an empty directory,
> we start the "move-head" call to switch from NULL to ce->oid without
> having any directory.  Wouldn't we want to mkdir() here (and remove
> mkdir() in submodule_move_head() if there is one---if there isn't
> then I do not think this codepath would work)?

In addition to mkdir(), would we also need the .git file that point
into superproject's .git/modules/ too?

Re: [PATCH 16/18] entry.c: update submodules when interesting

[Stefan Beller]

On Tue, Mar 7, 2017 at 3:04 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Junio C Hamano <gitster@pobox.com> writes:
>
>>> +                    if (!is_submodule_populated_gently(ce->name, &err)) {
>>> +                            struct stat sb;
>>> +                            if (lstat(ce->name, &sb))
>>> +                                    die(_("could not stat file '%s'"), ce->name);
>>> +                            if (!(st.st_mode & S_IFDIR))
>>> +                                    unlink_or_warn(ce->name);
>>
>> We found that the path ce->name is supposed to be a submodule that
>> is checked out, we found that the submodule is not yet populated, we
>> tried to make sure what is on that path, and its failure would cause
>> us to die().  All that is sensible.
>> ...
>> But if that unlink fails, shouldn't we die, just like the case where
>> we cannot tell what is at the path ce->name?
>>
>> And if that unlink succeeds, instead of having an empty directory,
>> we start the "move-head" call to switch from NULL to ce->oid without
>> having any directory.  Wouldn't we want to mkdir() here (and remove
>> mkdir() in submodule_move_head() if there is one---if there isn't
>> then I do not think this codepath would work)?
>
> In addition to mkdir(), would we also need the .git file that point
> into superproject's .git/modules/ too?

The move_head function takes care of it
Both creation as well as deletion are handled in the move_head function,
when either new or old is NULL.

We can drag that out of that function and have it at the appropriate places
manually.

Why do you think it is better design to have mkdir here and not in move_head?
(For me having everything in move_head was easier to understand,
maybe it is not for others)

Thanks,
Stefan

Re: [PATCH 15/18] read-cache, remove_marked_cache_entries: wipe selected submodules.

[Stefan Beller]

On Tue, Mar 7, 2017 at 2:42 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Stefan Beller <sbeller@google.com> writes:
>
>> Signed-off-by: Stefan Beller <sbeller@google.com>

>> +             submodule_move_head(sub->path, "HEAD", NULL, \
>
> What is this backslash doing here?

I am still bad at following coding conventions, apparently.
will remove.

>> @@ -532,8 +550,13 @@ void remove_marked_cache_entries(struct index_state *istate)
>>
>>       for (i = j = 0; i < istate->cache_nr; i++) {
>>               if (ce_array[i]->ce_flags & CE_REMOVE) {
>> -                     remove_name_hash(istate, ce_array[i]);
>> -                     save_or_free_index_entry(istate, ce_array[i]);
>> +                     const struct submodule *sub = submodule_from_ce(ce_array[i]);
>> +                     if (sub) {
>> +                             remove_submodule_according_to_strategy(sub);
>> +                     } else {
>> +                             remove_name_hash(istate, ce_array[i]);
>> +                             save_or_free_index_entry(istate, ce_array[i]);
>> +                     }
>
> I cannot readily tell as the proposed log message is on the sketchy
> side to explain the reasoning behind this, but this behaviour change
> is done unconditionally (in other words, without introducing a flag
> that is set by --recurse-submodules command line flag and switches
> behaviour based on the flag) here.  What is the end-user visible
> effect with this change?

submodule_from_ce returns always NULL, when such flag is not given.
From 10/18:

+const struct submodule *submodule_from_ce(const struct cache_entry *ce)
+{
+       if (!S_ISGITLINK(ce->ce_mode))
+               return NULL;
+
+       if (!should_update_submodules())
+               return NULL;
+
+       return submodule_from_path(null_sha1, ce->name);
+}

should_update_submodules is always false if such a flag is not set,
such that we end up in the else case which is literally the same as
the removed lines (they are just indented).

>  Can we have a new test in this same patch
> to demonstrate the desired behaviour introduced by this change (or
> the bug this change fixes)?

This doesn't fix a bug, but in case the flag is given (in patches 17,18)
this new code removes submodules that are no longer recorded in
the tree.

Re: [PATCH 16/18] entry.c: update submodules when interesting

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

>> In addition to mkdir(), would we also need the .git file that point
>> into superproject's .git/modules/ too?
>
> The move_head function takes care of it
> Both creation as well as deletion are handled in the move_head function,
> when either new or old is NULL.

Oh, if it does the creation of directory and adjusting of .git
gitfile, and handles other anomalies, I have no problem with it.

It was just that this codepath tried to handle some kind of anomaly
(namely, the user originally thought the submodule needs to be
changed to a regular file and then changed mind and wants to restore
it from the index) and yet not doing the full anomaly handling (like
"not even an empty directory exists" case) that confused me.

Re: [PATCH 15/18] read-cache, remove_marked_cache_entries: wipe selected submodules.

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> submodule_from_ce returns always NULL, when such flag is not given.
> From 10/18:
>
> +const struct submodule *submodule_from_ce(const struct cache_entry *ce)
> +{
> +       if (!S_ISGITLINK(ce->ce_mode))
> +               return NULL;
> +
> +       if (!should_update_submodules())
> +               return NULL;
> +
> +       return submodule_from_path(null_sha1, ce->name);
> +}
>
> should_update_submodules is always false if such a flag is not set,
> such that we end up in the else case which is literally the same as
> the removed lines (they are just indented).

I see.  

I didn't think a function this deep in the callchain that does not
take any parameter could possibly change the behaviour based on the
end-user input.  I was expecting that such a state (i.e. are we
recursive?  are we allowed to forcibly update the working tree
files?) would be kept part of something like "struct checkout" and
passed around the callchain.

That was why I didn't look at how that function answers "should
update?" question, and got puzzled.  Because it would imply there is
some hidden state that is accessible by everybody--a global variable
or something--which would point at a deeper design issue.

Re: [PATCH 15/18] read-cache, remove_marked_cache_entries: wipe selected submodules.

[Stefan Beller]

On Tue, Mar 7, 2017 at 5:14 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Stefan Beller <sbeller@google.com> writes:
>
>> submodule_from_ce returns always NULL, when such flag is not given.
>> From 10/18:
>>
>> +const struct submodule *submodule_from_ce(const struct cache_entry *ce)
>> +{
>> +       if (!S_ISGITLINK(ce->ce_mode))
>> +               return NULL;
>> +
>> +       if (!should_update_submodules())
>> +               return NULL;
>> +
>> +       return submodule_from_path(null_sha1, ce->name);
>> +}
>>
>> should_update_submodules is always false if such a flag is not set,
>> such that we end up in the else case which is literally the same as
>> the removed lines (they are just indented).
>
> I see.
>
> I didn't think a function this deep in the callchain that does not
> take any parameter could possibly change the behaviour based on the
> end-user input.  I was expecting that such a state (i.e. are we
> recursive?  are we allowed to forcibly update the working tree
> files?) would be kept part of something like "struct checkout" and
> passed around the callchain.
>
> That was why I didn't look at how that function answers "should
> update?" question, and got puzzled.  Because it would imply there is
> some hidden state that is accessible by everybody--a global variable
> or something--which would point at a deeper design issue.

Well it is just as deep as e.g. reacting on some bits of
struct unpack_trees_options in unpack-trees.c ?

But I can see how this is an issue with design.
I also think my previous answer was a straw man.

We only need to differentiate between 'ce' being a submodule
or not, because it should not be marked CE_REMOVE in
the non-recursive state.

Side-question:
Is there some doc (commit message), that explains the difference
between CE_REMOVE and CE_WT_REMOVE ?

Thanks,
Stefan

Re: [PATCH 15/18] read-cache, remove_marked_cache_entries: wipe selected submodules.

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> Side-question:
> Is there some doc (commit message), that explains the difference
> between CE_REMOVE and CE_WT_REMOVE ?

That's something you need to ask Duy, I think, as it was introduced
at e663db2f ("unpack-trees(): add CE_WT_REMOVE to remove on worktree
alone", 2009-08-20) and was added for the sparse checkout stuff.

During my review of the series that added the feature, I only had
time to make sure that the patches do not change the behaviour when
it is not in use, ignoring the other side of "if" statement that
checked ce_skip_worktree(ce) ;-)

[RFCv8 PATCH 00/17] Checkout aware of Submodules!

[Stefan Beller]

previous work:
https://public-inbox.org/git/20170306205919.9713-1-sbeller@google.com/

v8:
 * Thanks Ramsay; another variable is static now!
 * Thanks Junio; fixed typos (in comments and commit messages)!
 * dropped the patch touching read-cache.c; I realized it is bogus after
   inspecting it and trying to write a commit message.
 * All commits have commit messages now.
 * diff to Junios version below.
 
v7:
 * addressed Erics comment by fixing the bashism in t/lib-submodule-update.sh
diff to v6:
  diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
  index 5caae06bc5..949ebd546c 100755
  --- a/t/lib-submodule-update.sh
  +++ b/t/lib-submodule-update.sh
  @@ -255,7 +255,7 @@ test_superproject_content () {
   # Test that the given submodule at path "$1" contains the content according
   # to the submodule commit recorded in the superproject's commit "$2"
   test_submodule_content () {
  -       if test "$1" == "-C"
  +       if test x"$1" = "x-C"
          then
                  cd "$2"
                  shift; shift;
 * interdiff to v5 below
                  

v6:
 * added support for read-tree (see last patch) to see how generic the
   code of the previous patches is. I am pretty pleased with that patch.
 * marked two functions static. Thanks Ramsay!
 * fixed the recursive test; it still fails but it is the code that fails,
   not the test. For this I had to change the setup code slightly.
 * 2 new patches adding tiny refactoring to the submodule test lib.  
 * interdiff (to origin/sb/checkout-recurse-submodules, which is v5) below.

v5:
 * as v4 was the first version queued by Junio, we do have an interdiff below!
 * renamed functions
 * changed the API, now the caller has to take care of the submodule strategy
   themselves. (Note this can be different for different situations, e.g.
   when a submodule is deleted, we can do that for any strategy except none and
   !command. But for moving to a new state of the submodule we currently
   only implement "checkout" [unspecified defaults to checkout]. warning about
   the others, doing nothing there.)

v4:
 * addressed all comments of Brian, Junio and Brandon.
 Thanks!
 * one major point of change is the introduction of another patch
   "lib-submodule-update.sh: do not use ./. as submodule remote",
   as that took some time to track down the existing bug.
 
v3:
 * moved tests from t2013 to the generic submodule library.
 * factored out the refactoring patches to be up front
 * As I redid the complete implementation, I have the impression this time
   it is cleaner than previous versions.
 
 I think we still have to fix the corner cases of directory/file/submodule 
 conflicts before merging, but this serves as a status update on my current
 way of thinking how to implement the worktree commands being aware of
 submodules.
 
Thanks,
Stefan

v2:
* based on top of the series sent out an hour ago
  "[PATCHv4 0/5] submodule embedgitdirs"
* Try to embed a submodule if we need to remove it.
* Strictly do not change behavior if not giving the new flag.
* I think I missed some review comments from v1, but I'd like to get
  the current state out over the weekend, as a lot has changed so far.
  On Monday I'll go through the previous discussion with a comb to see
  if I missed something.
  
v1:
When working with submodules, nearly anytime after checking out
a different state of the projects, that has submodules changed
you'd run "git submodule update" with a current version of Git.

There are two problems with this approach:

* The "submodule update" command is dangerous as it
  doesn't check for work that may be lost in the submodule
  (e.g. a dangling commit).
* you may forget to run the command as checkout is supposed
  to do all the work for you.

Integrate updating the submodules into git checkout, with the same
safety promises that git-checkout has, i.e. not throw away data unless
asked to. This is done by first checking if the submodule is at the same
sha1 as it is recorded in the superproject. If there are changes we stop
proceeding the checkout just like it is when checking out a file that
has local changes.

The integration happens in the code that is also used in other commands
such that it will be easier in the future to make other commands aware
of submodule.

This also solves d/f conflicts in case you replace a file/directory
with a submodule or vice versa.

The patches are still a bit rough, but the overall series seems
promising enough to me that I want to put it out here.

Any review, specifically on the design level welcome!

Thanks,
Stefan
  
diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 2dc5cc06da..23e212ee8c 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -21,7 +21,7 @@
 static int nr_trees;
 static int read_empty;
 static struct tree *trees[MAX_UNPACK_TREES];
-int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
+static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 
 static int list_tree(unsigned char *sha1)
 {
diff --git a/read-cache.c b/read-cache.c
index 9a2abacf7a..9054369dd0 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -18,8 +18,6 @@
 #include "varint.h"
 #include "split-index.h"
 #include "utf8.h"
-#include "submodule.h"
-#include "submodule-config.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -522,22 +520,6 @@ int remove_index_entry_at(struct index_state *istate, int pos)
 	return 1;
 }
 
-static void remove_submodule_according_to_strategy(const struct submodule *sub)
-{
-	switch (sub->update_strategy.type) {
-	case SM_UPDATE_UNSPECIFIED:
-	case SM_UPDATE_CHECKOUT:
-	case SM_UPDATE_REBASE:
-	case SM_UPDATE_MERGE:
-		submodule_move_head(sub->path, "HEAD", NULL, \
-				    SUBMODULE_MOVE_HEAD_FORCE);
-		break;
-	case SM_UPDATE_NONE:
-	case SM_UPDATE_COMMAND:
-		; /* Do not touch the submodule. */
-	}
-}
-
 /*
  * Remove all cache entries marked for removal, that is where
  * CE_REMOVE is set in ce_flags.  This is much more effective than
@@ -550,13 +532,8 @@ void remove_marked_cache_entries(struct index_state *istate)
 
 	for (i = j = 0; i < istate->cache_nr; i++) {
 		if (ce_array[i]->ce_flags & CE_REMOVE) {
-			const struct submodule *sub = submodule_from_ce(ce_array[i]);
-			if (sub) {
-				remove_submodule_according_to_strategy(sub);
-			} else {
-				remove_name_hash(istate, ce_array[i]);
-				save_or_free_index_entry(istate, ce_array[i]);
-			}
+			remove_name_hash(istate, ce_array[i]);
+			save_or_free_index_entry(istate, ce_array[i]);
 		}
 		else
 			ce_array[j++] = ce_array[i];
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 949ebd546c..e195b590a1 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -954,7 +954,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 
-	# ... and ignored files are ignroed
+	# ... and ignored files are ignored
 	test_expect_success "$command: replace submodule with a file works ignores ignored files in submodule" '
 		test_when_finished "rm submodule_update/.git/modules/sub1/info/exclude" &&
 		prolog &&

[PATCH 01/17] lib-submodule-update.sh: reorder create_lib_submodule_repo

[Stefan Beller]

Redraw the ASCII art describing the setup using more space, such that
it is easier to understand.  The leaf commits are now ordered the same
way the actual code is ordered.

Add empty lines to the setup code separating each of the leaf commits,
each starting with a "checkout -b".

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 49 ++++++++++++++++++++++++++++-------------------
 1 file changed, 29 insertions(+), 20 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 915eb4a7c6..5df528ea81 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -15,22 +15,27 @@
 # - Tracked file replaced by submodule (replace_sub1_with_file =>
 #   replace_file_with_sub1)
 #
-#                   --O-----O
-#                  /  ^     replace_directory_with_sub1
-#                 /   replace_sub1_with_directory
-#                /----O
-#               /     ^
-#              /      modify_sub1
-#      O------O-------O
-#      ^      ^\      ^
-#      |      | \     remove_sub1
-#      |      |  -----O-----O
-#      |      |   \   ^     replace_file_with_sub1
-#      |      |    \  replace_sub1_with_file
-#      |   add_sub1 --O-----O
-# no_submodule        ^     valid_sub1
-#                     invalid_sub1
+#                     ----O
+#                    /    ^
+#                   /     remove_sub1
+#                  /
+#       add_sub1  /-------O
+#             |  /        ^
+#             | /         modify_sub1
+#             v/
+#      O------O-----------O---------O
+#      ^       \          ^         replace_directory_with_sub1
+#      |        \         replace_sub1_with_directory
+# no_submodule   \
+#                 --------O---------O
+#                  \      ^         replace_file_with_sub1
+#                   \     replace_sub1_with_file
+#                    \
+#                     ----O---------O
+#                         ^         valid_sub1
+#                         invalid_sub1
 #
+
 create_lib_submodule_repo () {
 	git init submodule_update_repo &&
 	(
@@ -49,10 +54,11 @@ create_lib_submodule_repo () {
 		git config submodule.sub1.ignore all &&
 		git add .gitmodules &&
 		git commit -m "Add sub1" &&
-		git checkout -b remove_sub1 &&
+
+		git checkout -b remove_sub1 add_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "modify_sub1" "add_sub1" &&
+		git checkout -b modify_sub1 add_sub1 &&
 		git submodule update &&
 		(
 			cd sub1 &&
@@ -67,7 +73,7 @@ create_lib_submodule_repo () {
 		git add sub1 &&
 		git commit -m "Modify sub1" &&
 
-		git checkout -b "replace_sub1_with_directory" "add_sub1" &&
+		git checkout -b replace_sub1_with_directory add_sub1 &&
 		git submodule update &&
 		git -C sub1 checkout modifications &&
 		git rm --cached sub1 &&
@@ -75,22 +81,25 @@ create_lib_submodule_repo () {
 		git config -f .gitmodules --remove-section "submodule.sub1" &&
 		git add .gitmodules sub1/* &&
 		git commit -m "Replace sub1 with directory" &&
+
 		git checkout -b replace_directory_with_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "replace_sub1_with_file" "add_sub1" &&
+		git checkout -b replace_sub1_with_file add_sub1 &&
 		git rm sub1 &&
 		echo "content" >sub1 &&
 		git add sub1 &&
 		git commit -m "Replace sub1 with file" &&
+
 		git checkout -b replace_file_with_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "invalid_sub1" "add_sub1" &&
+		git checkout -b invalid_sub1 add_sub1 &&
 		git update-index --cacheinfo 160000 0123456789012345678901234567890123456789 sub1 &&
 		git commit -m "Invalid sub1 commit" &&
 		git checkout -b valid_sub1 &&
 		git revert HEAD &&
+
 		git checkout master
 	)
 }
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 02/17] lib-submodule-update.sh: do not use ./. as submodule remote

[Stefan Beller]

Adding the repository itself as a submodule does not make sense in the
real world. In our test suite we used to do that out of convenience in
some tests as the current repository has easiest access for setting up
'just a submodule'.

However this doesn't quite test the real world, so let's do not follow
this pattern any further and actually create an independent repository
that we can use as a submodule.

When using './.' as the remote the superproject and submodule share the
same objects, such that testing if a given sha1 is a valid commit works
in either repository.  As running commands in an unpopulated submodule
fall back to the superproject, this happens in `reset_work_tree_to`
to determine if we need to populate the submodule. Fix this bug by
checking in the actual remote now.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 5df528ea81..c0d6325133 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -37,6 +37,17 @@
 #
 
 create_lib_submodule_repo () {
+	git init submodule_update_sub1 &&
+	(
+		cd submodule_update_sub1 &&
+		echo "expect" >>.gitignore &&
+		echo "actual" >>.gitignore &&
+		echo "x" >file1 &&
+		echo "y" >file2 &&
+		git add .gitignore file1 file2 &&
+		git commit -m "Base inside first submodule" &&
+		git branch "no_submodule"
+	) &&
 	git init submodule_update_repo &&
 	(
 		cd submodule_update_repo &&
@@ -49,7 +60,7 @@ create_lib_submodule_repo () {
 		git branch "no_submodule" &&
 
 		git checkout -b "add_sub1" &&
-		git submodule add ./. sub1 &&
+		git submodule add ../submodule_update_sub1 sub1 &&
 		git config -f .gitmodules submodule.sub1.ignore all &&
 		git config submodule.sub1.ignore all &&
 		git add .gitmodules &&
@@ -162,7 +173,7 @@ reset_work_tree_to () {
 		test_must_be_empty actual &&
 		sha1=$(git rev-parse --revs-only HEAD:sub1) &&
 		if test -n "$sha1" &&
-		   test $(cd "sub1" && git rev-parse --verify "$sha1^{commit}")
+		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$sha1^{commit}")
 		then
 			git submodule update --init --recursive "sub1"
 		fi
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 03/17] lib-submodule-update: teach test_submodule_content the -C <dir> flag

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index c0d6325133..00128f28b5 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -193,6 +193,11 @@ test_superproject_content () {
 # Test that the given submodule at path "$1" contains the content according
 # to the submodule commit recorded in the superproject's commit "$2"
 test_submodule_content () {
+	if test x"$1" = "x-C"
+	then
+		cd "$2"
+		shift; shift;
+	fi
 	if test $# != 2
 	then
 		echo "test_submodule_content needs two arguments"
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 04/17] lib-submodule-update.sh: replace sha1 by hash

[Stefan Beller]

Cleaning up code by generalising it.
Currently the mailing list discusses yet again how
to migrate away from sha1.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 00128f28b5..f52c49c838 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -171,9 +171,9 @@ reset_work_tree_to () {
 		git checkout -f "$1" &&
 		git status -u -s >actual &&
 		test_must_be_empty actual &&
-		sha1=$(git rev-parse --revs-only HEAD:sub1) &&
-		if test -n "$sha1" &&
-		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$sha1^{commit}")
+		hash=$(git rev-parse --revs-only HEAD:sub1) &&
+		if test -n "$hash" &&
+		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$hash^{commit}")
 		then
 			git submodule update --init --recursive "sub1"
 		fi
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 05/17] lib-submodule-update.sh: define tests for recursing into submodules

[Stefan Beller]

Currently lib-submodule-update.sh provides 2 functions
test_submodule_switch and test_submodule_forced_switch that are used by a
variety of tests to ensure that submodules behave as expected. The current
expected behavior is that submodules are not touched at all (see
42639d2317a for the exact setup).

In the future we want to teach all these commands to recurse
into submodules. To do that, we'll add two testing functions to
submodule-update-lib.sh: test_submodule_switch_recursing and
test_submodule_forced_switch_recursing.

These two functions behave in analogy to the already existing functions
just with a different expectation on submodule behavior. The submodule
in the working tree is expected to be updated to the recorded submodule
version. The behavior is analogous to e.g. the behavior of files in a
nested directory in the working tree, where a change to the working tree
handles any arising directory/file conflicts just fine.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 506 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 504 insertions(+), 2 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index f52c49c838..deba618bee 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -4,6 +4,7 @@
 # - New submodule (no_submodule => add_sub1)
 # - Removed submodule (add_sub1 => remove_sub1)
 # - Updated submodule (add_sub1 => modify_sub1)
+# - Updated submodule recursively (add_nested_sub => modify_sub1_recursively)
 # - Submodule updated to invalid commit (add_sub1 => invalid_sub1)
 # - Submodule updated from invalid commit (invalid_sub1 => valid_sub1)
 # - Submodule replaced by tracked files in directory (add_sub1 =>
@@ -19,8 +20,8 @@
 #                    /    ^
 #                   /     remove_sub1
 #                  /
-#       add_sub1  /-------O
-#             |  /        ^
+#       add_sub1  /-------O---------O--------O  modify_sub1_recursively
+#             |  /        ^         add_nested_sub
 #             | /         modify_sub1
 #             v/
 #      O------O-----------O---------O
@@ -48,6 +49,17 @@ create_lib_submodule_repo () {
 		git commit -m "Base inside first submodule" &&
 		git branch "no_submodule"
 	) &&
+	git init submodule_update_sub2 &&
+	(
+		cd submodule_update_sub2
+		echo "expect" >>.gitignore &&
+		echo "actual" >>.gitignore &&
+		echo "x" >file1 &&
+		echo "y" >file2 &&
+		git add .gitignore file1 file2 &&
+		git commit -m "nested submodule base" &&
+		git branch "no_submodule"
+	) &&
 	git init submodule_update_repo &&
 	(
 		cd submodule_update_repo &&
@@ -84,6 +96,26 @@ create_lib_submodule_repo () {
 		git add sub1 &&
 		git commit -m "Modify sub1" &&
 
+		git checkout -b add_nested_sub modify_sub1 &&
+		git -C sub1 checkout -b "add_nested_sub" &&
+		git -C sub1 submodule add --branch no_submodule ../submodule_update_sub2 sub2 &&
+		git -C sub1 commit -a -m "add a nested submodule" &&
+		git add sub1 &&
+		git commit -a -m "update submodule, that updates a nested submodule" &&
+		git checkout -b modify_sub1_recursively &&
+		git -C sub1 checkout -b modify_sub1_recursively &&
+		git -C sub1/sub2 checkout -b modify_sub1_recursively &&
+		echo change >sub1/sub2/file3 &&
+		git -C sub1/sub2 add file3 &&
+		git -C sub1/sub2 commit -m "make a change in nested sub" &&
+		git -C sub1 add sub2 &&
+		git -C sub1 commit -m "update nested sub" &&
+		git add sub1 &&
+		git commit -m "update sub1, that updates nested sub" &&
+		git -C sub1 push origin modify_sub1_recursively &&
+		git -C sub1/sub2 push origin modify_sub1_recursively &&
+		git -C sub1 submodule deinit -f --all &&
+
 		git checkout -b replace_sub1_with_directory add_sub1 &&
 		git submodule update &&
 		git -C sub1 checkout modifications &&
@@ -150,6 +182,15 @@ test_git_directory_is_unchanged () {
 	)
 }
 
+test_git_directory_exists() {
+	test -e ".git/modules/$1" &&
+	if test -f sub1/.git
+	then
+		# does core.worktree point at the right place?
+		test "$(git -C .git/modules/$1 config core.worktree)" = "../../../$1"
+	fi
+}
+
 # Helper function to be executed at the start of every test below, it sets up
 # the submodule repo if it doesn't exist and configures the most problematic
 # settings for diff.ignoreSubmodules.
@@ -180,6 +221,27 @@ reset_work_tree_to () {
 	)
 }
 
+reset_work_tree_to_interested () {
+	reset_work_tree_to $1 &&
+	# make the submodule git dirs available
+	if ! test -d submodule_update/.git/modules/sub1
+	then
+		mkdir -p submodule_update/.git/modules &&
+		cp -r submodule_update_repo/.git/modules/sub1 submodule_update/.git/modules/sub1
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1 config --unset core.worktree
+	fi &&
+	if ! test -d submodule_update/.git/modules/sub1/modules/sub2
+	then
+		mkdir -p submodule_update/.git/modules/sub1/modules &&
+		cp -r submodule_update_repo/.git/modules/sub1/modules/sub2 submodule_update/.git/modules/sub1/modules/sub2
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1/modules/sub2 config --unset core.worktree
+	fi &&
+	# indicate we are interested in the submodule:
+	git -C submodule_update config submodule.sub1.url "bogus" &&
+	# sub1 might not be checked out, so use the git dir
+	git -C submodule_update/.git/modules/sub1 config submodule.sub2.url "bogus"
+}
+
 # Test that the superproject contains the content according to commit "$1"
 # (the work tree must match the index for everything but submodules but the
 # index must exactly match the given commit including any submodule SHA-1s).
@@ -700,3 +762,443 @@ test_submodule_forced_switch () {
 		)
 	'
 }
+
+# Test that submodule contents are correctly updated when switching
+# between commits that change a submodule.
+# Test that the following transitions are correctly handled:
+# (These tests are also above in the case where we expect no change
+#  in the submodule)
+# - Updated submodule
+# - New submodule
+# - Removed submodule
+# - Directory containing tracked files replaced by submodule
+# - Submodule replaced by tracked files in directory
+# - Submodule replaced by tracked file with the same name
+# - tracked file replaced by submodule
+#
+# New test cases
+# - Removing a submodule with a git directory absorbs the submodules
+#   git directory first into the superproject.
+
+test_submodule_switch_recursing () {
+	command="$1"
+	######################### Appearing submodule #########################
+	# Switching to a commit letting a submodule appear checks it out ...
+	test_expect_success "$command: added submodule is checked out" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... ignoring an empty existing directory ...
+	test_expect_success "$command: added submodule is checked out in empty dir" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			mkdir sub1 &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... unless there is an untracked file in its place.
+	test_expect_success "$command: added submodule doesn't remove untracked file with same name" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			: >sub1 &&
+			test_must_fail $command add_sub1 &&
+			test_superproject_content origin/no_submodule &&
+			test_must_be_empty sub1
+		)
+	'
+	# ... but an ignored file is fine.
+	test_expect_success "$command: added submodule removes an untracked ignored file" '
+		test_when_finished "rm submodule_update/.git/info/exclude" &&
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			: >sub1 &&
+			echo sub1 >.git/info/exclude
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Replacing a tracked file with a submodule produces a checked out submodule
+	test_expect_success "$command: replace tracked file with submodule checks out submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_file &&
+		(
+			cd submodule_update &&
+			git branch -t replace_file_with_sub1 origin/replace_file_with_sub1 &&
+			$command replace_file_with_sub1 &&
+			test_superproject_content origin/replace_file_with_sub1 &&
+			test_submodule_content sub1 origin/replace_file_with_sub1
+		)
+	'
+	# ... as does removing a directory with tracked files with a submodule.
+	test_expect_success "$command: replace directory with submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_directory &&
+		(
+			cd submodule_update &&
+			git branch -t replace_directory_with_sub1 origin/replace_directory_with_sub1 &&
+			$command replace_directory_with_sub1 &&
+			test_superproject_content origin/replace_directory_with_sub1 &&
+			test_submodule_content sub1 origin/replace_directory_with_sub1
+		)
+	'
+
+	######################## Disappearing submodule #######################
+	# Removing a submodule removes its work tree ...
+	test_expect_success "$command: removed submodule removes submodules working tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1
+		)
+	'
+	# ... absorbing a .git directory along the way.
+	test_expect_success "$command: removed submodule absorbs submodules .git directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1 &&
+			test_git_directory_exists sub1
+		)
+	'
+	# Replacing a submodule with files in a directory must succeeds
+	# when the submodule is clean
+	test_expect_success "$command: replace submodule with a directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_submodule_content sub1 origin/replace_sub1_with_directory
+		)
+	'
+	# ... absorbing a .git directory.
+	test_expect_success "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_git_directory_exists sub1
+		)
+	'
+
+	# Replacing it with a file ...
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file &&
+			test -f sub1
+		)
+	'
+
+	# ... must check its local work tree for untracked files
+	test_expect_success "$command: replace submodule with a file must fail with untracked files" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/untrackedfile &&
+			test_must_fail $command replace_sub1_with_file &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+
+	# ... and ignored files are ignored
+	test_expect_success "$command: replace submodule with a file works ignores ignored files in submodule" '
+		test_when_finished "rm submodule_update/.git/modules/sub1/info/exclude" &&
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/ignored &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file &&
+			test -f sub1
+		)
+	'
+
+	########################## Modified submodule #########################
+	# Updating a submodule sha1 updates the submodule's work tree
+	test_expect_success "$command: modified submodule updates submodule work tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1 origin/modify_sub1 &&
+			$command modify_sub1 &&
+			test_superproject_content origin/modify_sub1 &&
+			test_submodule_content sub1 origin/modify_sub1
+		)
+	'
+
+	# Updating a submodule to an invalid sha1 doesn't update the
+	# superproject nor the submodule's work tree.
+	test_expect_success "$command: updating to a missing submodule commit fails" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t invalid_sub1 origin/invalid_sub1 &&
+			test_must_fail $command invalid_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+
+	test_expect_success "$command: modified submodule updates submodule recursively" '
+		prolog &&
+		reset_work_tree_to_interested add_nested_sub &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1_recursively origin/modify_sub1_recursively &&
+			$command modify_sub1_recursively &&
+			test_superproject_content origin/modify_sub1_recursively &&
+			test_submodule_content sub1 origin/modify_sub1_recursively &&
+			test_submodule_content -C sub1 sub2 origin/modify_sub1_recursively
+		)
+	'
+}
+
+# Test that submodule contents are updated when switching between commits
+# that change a submodule, but throwing away local changes in
+# the superproject as well as the submodule is allowed.
+test_submodule_forced_switch_recursing () {
+	command="$1"
+	######################### Appearing submodule #########################
+	# Switching to a commit letting a submodule appear creates empty dir ...
+	test_expect_success "$command: added submodule is checked out" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... and doesn't care if it already exists ...
+	test_expect_success "$command: added submodule ignores empty directory" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			mkdir sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... not caring about an untracked file either
+	test_expect_success "$command: added submodule does remove untracked unignored file with same name when forced" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			>sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Replacing a tracked file with a submodule checks out the submodule
+	test_expect_success "$command: replace tracked file with submodule populates the submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_file &&
+		(
+			cd submodule_update &&
+			git branch -t replace_file_with_sub1 origin/replace_file_with_sub1 &&
+			$command replace_file_with_sub1 &&
+			test_superproject_content origin/replace_file_with_sub1 &&
+			test_submodule_content sub1 origin/replace_file_with_sub1
+		)
+	'
+	# ... as does removing a directory with tracked files with a
+	# submodule.
+	test_expect_success "$command: replace directory with submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_directory &&
+		(
+			cd submodule_update &&
+			git branch -t replace_directory_with_sub1 origin/replace_directory_with_sub1 &&
+			$command replace_directory_with_sub1 &&
+			test_superproject_content origin/replace_directory_with_sub1 &&
+			test_submodule_content sub1 origin/replace_directory_with_sub1
+		)
+	'
+
+	######################## Disappearing submodule #######################
+	# Removing a submodule doesn't remove its work tree ...
+	test_expect_success "$command: removed submodule leaves submodule directory and its contents in place" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1
+		)
+	'
+	# ... especially when it contains a .git directory.
+	test_expect_success "$command: removed submodule leaves submodule containing a .git directory alone" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules/sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			test_git_directory_exists sub1 &&
+			! test -e sub1
+		)
+	'
+	# Replacing a submodule with files in a directory ...
+	test_expect_success "$command: replace submodule with a directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			test_must_fail $command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory
+		)
+	'
+	# ... absorbing a .git directory.
+	test_expect_success "$command: replace submodule containing a .git directory with a directory must fail" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules/sub1 &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_submodule_content sub1 origin/modify_sub1
+			test_git_directory_exists sub1
+		)
+	'
+	# Replacing it with a file
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file
+		)
+	'
+
+	# ... even if the submodule contains ignored files
+	test_expect_success "$command: replace submodule with a file ignoring ignored files" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/expect &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file
+		)
+	'
+
+	# ... but stops for untracked files that would be lost
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/untracked_file &&
+			test_must_fail $command replace_sub1_with_file &&
+			test_superproject_content origin/add_sub1 &&
+			test -f sub1/untracked_file
+		)
+	'
+
+	########################## Modified submodule #########################
+	# Updating a submodule sha1 updates the submodule's work tree
+	test_expect_success "$command: modified submodule updates submodule work tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1 origin/modify_sub1 &&
+			$command modify_sub1 &&
+			test_superproject_content origin/modify_sub1 &&
+			test_submodule_content sub1 origin/modify_sub1
+		)
+	'
+	# Updating a submodule to an invalid sha1 doesn't update the
+	# submodule's work tree, subsequent update will fail
+	test_expect_success "$command: modified submodule does not update submodule work tree to invalid commit" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t invalid_sub1 origin/invalid_sub1 &&
+			test_must_fail $command invalid_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Updating a submodule from an invalid sha1 updates
+	test_expect_success "$command: modified submodule does not update submodule work tree from invalid commit" '
+		prolog &&
+		reset_work_tree_to_interested invalid_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t valid_sub1 origin/valid_sub1 &&
+			test_must_fail $command valid_sub1 &&
+			test_superproject_content origin/invalid_sub1
+		)
+	'
+}
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 06/17] make is_submodule_populated gently

[Stefan Beller]

We need the gentle version in a later patch. As we have just one caller,
migrate the caller.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/grep.c | 2 +-
 submodule.c    | 7 ++-----
 submodule.h    | 8 +++++++-
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/builtin/grep.c b/builtin/grep.c
index 2c727ef499..b17835aed6 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -616,7 +616,7 @@ static int grep_submodule(struct grep_opt *opt, const unsigned char *sha1,
 {
 	if (!is_submodule_initialized(path))
 		return 0;
-	if (!is_submodule_populated(path)) {
+	if (!is_submodule_populated_gently(path, NULL)) {
 		/*
 		 * If searching history, check for the presense of the
 		 * submodule's gitdir before skipping the submodule.
diff --git a/submodule.c b/submodule.c
index 3b98766a6b..0e55372f37 100644
--- a/submodule.c
+++ b/submodule.c
@@ -234,15 +234,12 @@ int is_submodule_initialized(const char *path)
 	return ret;
 }
 
-/*
- * Determine if a submodule has been populated at a given 'path'
- */
-int is_submodule_populated(const char *path)
+int is_submodule_populated_gently(const char *path, int *return_error_code)
 {
 	int ret = 0;
 	char *gitdir = xstrfmt("%s/.git", path);
 
-	if (resolve_gitdir(gitdir))
+	if (resolve_gitdir_gently(gitdir, return_error_code))
 		ret = 1;
 
 	free(gitdir);
diff --git a/submodule.h b/submodule.h
index 05ab674f06..0b915bd3ac 100644
--- a/submodule.h
+++ b/submodule.h
@@ -41,7 +41,13 @@ extern int submodule_config(const char *var, const char *value, void *cb);
 extern void gitmodules_config(void);
 extern void gitmodules_config_sha1(const unsigned char *commit_sha1);
 extern int is_submodule_initialized(const char *path);
-extern int is_submodule_populated(const char *path);
+/*
+ * Determine if a submodule has been populated at a given 'path' by checking if
+ * the <path>/.git resolves to a valid git repository.
+ * If return_error_code is NULL, die on error.
+ * Otherwise the return error code is the same as of resolve_gitdir_gently.
+ */
+extern int is_submodule_populated_gently(const char *path, int *return_error_code);
 extern int parse_submodule_update_strategy(const char *value,
 		struct submodule_update_strategy *dst);
 extern const char *submodule_strategy_to_string(const struct submodule_update_strategy *s);
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 07/17] connect_work_tree_and_git_dir: safely create leading directories

[Stefan Beller]

In a later patch we'll use connect_work_tree_and_git_dir when the
directory for the gitlink file doesn't exist yet. This patch makes
connect_work_tree_and_git_dir safe to use for both cases of
either the git dir or the working dir missing.

To do so, we need to call safe_create_leading_directories[_const]
on both directories. However this has to happen before we construct
the absolute paths as real_pathdup assumes the directories to
be there already.

So for both the config file in the git dir as well as the .git link
file we need to
a) construct the name
b) call SCLD
c) get the absolute path
d) once a-c is done for both we can consume the absolute path
   to compute the relative path to each other and store those
   relative paths.

The implementation provided here puts a) and b) for both cases first,
and then performs c and d after.

One of the two users of 'connect_work_tree_and_git_dir' already checked
for the directory being there, so we can loose that check as
connect_work_tree_and_git_dir handles this functionality now.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 dir.c       | 32 +++++++++++++++++++++-----------
 submodule.c | 11 ++---------
 2 files changed, 23 insertions(+), 20 deletions(-)

diff --git a/dir.c b/dir.c
index 4541f9e146..6f52af7abb 100644
--- a/dir.c
+++ b/dir.c
@@ -2728,23 +2728,33 @@ void untracked_cache_add_to_index(struct index_state *istate,
 /* Update gitfile and core.worktree setting to connect work tree and git dir */
 void connect_work_tree_and_git_dir(const char *work_tree_, const char *git_dir_)
 {
-	struct strbuf file_name = STRBUF_INIT;
+	struct strbuf gitfile_sb = STRBUF_INIT;
+	struct strbuf cfg_sb = STRBUF_INIT;
 	struct strbuf rel_path = STRBUF_INIT;
-	char *git_dir = real_pathdup(git_dir_);
-	char *work_tree = real_pathdup(work_tree_);
+	char *git_dir, *work_tree;
 
-	/* Update gitfile */
-	strbuf_addf(&file_name, "%s/.git", work_tree);
-	write_file(file_name.buf, "gitdir: %s",
-		   relative_path(git_dir, work_tree, &rel_path));
+	/* Prepare .git file */
+	strbuf_addf(&gitfile_sb, "%s/.git", work_tree_);
+	if (safe_create_leading_directories_const(gitfile_sb.buf))
+		die(_("could not create directories for %s"), gitfile_sb.buf);
+
+	/* Prepare config file */
+	strbuf_addf(&cfg_sb, "%s/config", git_dir_);
+	if (safe_create_leading_directories_const(cfg_sb.buf))
+		die(_("could not create directories for %s"), cfg_sb.buf);
 
+	git_dir = real_pathdup(git_dir_);
+	work_tree = real_pathdup(work_tree_);
+
+	/* Write .git file */
+	write_file(gitfile_sb.buf, "gitdir: %s",
+		   relative_path(git_dir, work_tree, &rel_path));
 	/* Update core.worktree setting */
-	strbuf_reset(&file_name);
-	strbuf_addf(&file_name, "%s/config", git_dir);
-	git_config_set_in_file(file_name.buf, "core.worktree",
+	git_config_set_in_file(cfg_sb.buf, "core.worktree",
 			       relative_path(work_tree, git_dir, &rel_path));
 
-	strbuf_release(&file_name);
+	strbuf_release(&gitfile_sb);
+	strbuf_release(&cfg_sb);
 	strbuf_release(&rel_path);
 	free(work_tree);
 	free(git_dir);
diff --git a/submodule.c b/submodule.c
index 0e55372f37..04d185738f 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1442,8 +1442,6 @@ void absorb_git_dir_into_superproject(const char *prefix,
 
 	/* Not populated? */
 	if (!sub_git_dir) {
-		char *real_new_git_dir;
-		const char *new_git_dir;
 		const struct submodule *sub;
 
 		if (err_code == READ_GITFILE_ERR_STAT_FAILED) {
@@ -1466,13 +1464,8 @@ void absorb_git_dir_into_superproject(const char *prefix,
 		sub = submodule_from_path(null_sha1, path);
 		if (!sub)
 			die(_("could not lookup name for submodule '%s'"), path);
-		new_git_dir = git_path("modules/%s", sub->name);
-		if (safe_create_leading_directories_const(new_git_dir) < 0)
-			die(_("could not create directory '%s'"), new_git_dir);
-		real_new_git_dir = real_pathdup(new_git_dir);
-		connect_work_tree_and_git_dir(path, real_new_git_dir);
-
-		free(real_new_git_dir);
+		connect_work_tree_and_git_dir(path,
+			git_path("modules/%s", sub->name));
 	} else {
 		/* Is it already absorbed into the superprojects git dir? */
 		char *real_sub_git_dir = real_pathdup(sub_git_dir);
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 08/17] update submodules: add submodule config parsing

[Stefan Beller]

Similar to b33a15b08 (push: add recurseSubmodules config option,
2015-11-17) and 027771fcb1 (submodule: allow erroneous values for the
fetchRecurseSubmodules option, 2015-08-17), we add submodule-config code
that is later used to parse whether we are interested in updating
submodules.

We need the `die_on_error` parameter to be able to call this parsing
function for the config file as well, which if incorrect lets Git die.

As we're just touching the header file, also mark all functions extern.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule-config.c | 20 ++++++++++++++++++++
 submodule-config.h | 17 +++++++++--------
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/submodule-config.c b/submodule-config.c
index 93453909cf..3e8e380d98 100644
--- a/submodule-config.c
+++ b/submodule-config.c
@@ -234,6 +234,26 @@ int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg)
 	return parse_fetch_recurse(opt, arg, 1);
 }
 
+static int parse_update_recurse(const char *opt, const char *arg,
+				int die_on_error)
+{
+	switch (git_config_maybe_bool(opt, arg)) {
+	case 1:
+		return RECURSE_SUBMODULES_ON;
+	case 0:
+		return RECURSE_SUBMODULES_OFF;
+	default:
+		if (die_on_error)
+			die("bad %s argument: %s", opt, arg);
+		return RECURSE_SUBMODULES_ERROR;
+	}
+}
+
+int parse_update_recurse_submodules_arg(const char *opt, const char *arg)
+{
+	return parse_update_recurse(opt, arg, 1);
+}
+
 static int parse_push_recurse(const char *opt, const char *arg,
 			       int die_on_error)
 {
diff --git a/submodule-config.h b/submodule-config.h
index 70f19363fd..d434ecdb45 100644
--- a/submodule-config.h
+++ b/submodule-config.h
@@ -22,16 +22,17 @@ struct submodule {
 	int recommend_shallow;
 };
 
-int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg);
-int parse_push_recurse_submodules_arg(const char *opt, const char *arg);
-int parse_submodule_config_option(const char *var, const char *value);
-const struct submodule *submodule_from_name(const unsigned char *commit_or_tree,
-		const char *name);
-const struct submodule *submodule_from_path(const unsigned char *commit_or_tree,
-		const char *path);
+extern int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_update_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_push_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_submodule_config_option(const char *var, const char *value);
+extern const struct submodule *submodule_from_name(
+		const unsigned char *commit_or_tree, const char *name);
+extern const struct submodule *submodule_from_path(
+		const unsigned char *commit_or_tree, const char *path);
 extern int gitmodule_sha1_from_commit(const unsigned char *commit_sha1,
 				      unsigned char *gitmodules_sha1,
 				      struct strbuf *rev);
-void submodule_free(void);
+extern void submodule_free(void);
 
 #endif /* SUBMODULE_CONFIG_H */
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 09/17] update submodules: add a config option to determine if submodules are updated

[Stefan Beller]

In later patches we introduce the options and flag for commands
that modify the working directory, e.g. git-checkout.

Have a central place to store such settings whether we want to update
a submodule.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 6 ++++++
 submodule.h | 1 +
 2 files changed, 7 insertions(+)

diff --git a/submodule.c b/submodule.c
index 04d185738f..591f4a694e 100644
--- a/submodule.c
+++ b/submodule.c
@@ -17,6 +17,7 @@
 #include "worktree.h"
 
 static int config_fetch_recurse_submodules = RECURSE_SUBMODULES_ON_DEMAND;
+static int config_update_recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 static int parallel_jobs = 1;
 static struct string_list changed_submodule_paths = STRING_LIST_INIT_NODUP;
 static int initialized_fetch_ref_tips;
@@ -542,6 +543,11 @@ void set_config_fetch_recurse_submodules(int value)
 	config_fetch_recurse_submodules = value;
 }
 
+void set_config_update_recurse_submodules(int value)
+{
+	config_update_recurse_submodules = value;
+}
+
 static int has_remote(const char *refname, const struct object_id *oid,
 		      int flags, void *cb_data)
 {
diff --git a/submodule.h b/submodule.h
index 0b915bd3ac..b4e60c08d2 100644
--- a/submodule.h
+++ b/submodule.h
@@ -64,6 +64,7 @@ extern void show_submodule_inline_diff(FILE *f, const char *path,
 		const char *del, const char *add, const char *reset,
 		const struct diff_options *opt);
 extern void set_config_fetch_recurse_submodules(int value);
+extern void set_config_update_recurse_submodules(int value);
 extern void check_for_new_submodule_commits(unsigned char new_sha1[20]);
 extern int fetch_populated_submodules(const struct argv_array *options,
 			       const char *prefix, int command_line_option,
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 10/17] submodules: introduce check to see whether to touch a submodule

[Stefan Beller]

In later patches we introduce the --recurse-submodule flag for commands
that modify the working directory, e.g. git-checkout.

It is potentially expensive to check if a submodule needs an update,
because a common theme to interact with submodules is to spawn a child
process for each interaction.

So let's introduce a function that checks if a submodule needs
to be checked for an update before attempting the update.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 16 ++++++++++++++++
 submodule.h |  7 +++++++
 2 files changed, 23 insertions(+)

diff --git a/submodule.c b/submodule.c
index 591f4a694e..8b2c0212be 100644
--- a/submodule.c
+++ b/submodule.c
@@ -548,6 +548,22 @@ void set_config_update_recurse_submodules(int value)
 	config_update_recurse_submodules = value;
 }
 
+int should_update_submodules(void)
+{
+	return config_update_recurse_submodules == RECURSE_SUBMODULES_ON;
+}
+
+const struct submodule *submodule_from_ce(const struct cache_entry *ce)
+{
+	if (!S_ISGITLINK(ce->ce_mode))
+		return NULL;
+
+	if (!should_update_submodules())
+		return NULL;
+
+	return submodule_from_path(null_sha1, ce->name);
+}
+
 static int has_remote(const char *refname, const struct object_id *oid,
 		      int flags, void *cb_data)
 {
diff --git a/submodule.h b/submodule.h
index b4e60c08d2..6f3fe85c7c 100644
--- a/submodule.h
+++ b/submodule.h
@@ -65,6 +65,13 @@ extern void show_submodule_inline_diff(FILE *f, const char *path,
 		const struct diff_options *opt);
 extern void set_config_fetch_recurse_submodules(int value);
 extern void set_config_update_recurse_submodules(int value);
+/* Check if we want to update any submodule.*/
+extern int should_update_submodules(void);
+/*
+ * Returns the submodule struct if the given ce entry is a submodule
+ * and it should be updated. Returns NULL otherwise.
+ */
+extern const struct submodule *submodule_from_ce(const struct cache_entry *ce);
 extern void check_for_new_submodule_commits(unsigned char new_sha1[20]);
 extern int fetch_populated_submodules(const struct argv_array *options,
 			       const char *prefix, int command_line_option,
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 11/17] update submodules: move up prepare_submodule_repo_env

[Stefan Beller]

In a later patch we need to prepare the submodule environment with
another git directory, so split up the function.

Also move it up in the file such that we do not need to declare the
function later before using it.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/submodule.c b/submodule.c
index 8b2c0212be..0b2596e88a 100644
--- a/submodule.c
+++ b/submodule.c
@@ -356,6 +356,23 @@ static void print_submodule_summary(struct rev_info *rev, FILE *f,
 	strbuf_release(&sb);
 }
 
+static void prepare_submodule_repo_env_no_git_dir(struct argv_array *out)
+{
+	const char * const *var;
+
+	for (var = local_repo_env; *var; var++) {
+		if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
+			argv_array_push(out, *var);
+	}
+}
+
+void prepare_submodule_repo_env(struct argv_array *out)
+{
+	prepare_submodule_repo_env_no_git_dir(out);
+	argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
+			 DEFAULT_GIT_DIR_ENVIRONMENT);
+}
+
 /* Helper function to display the submodule header line prior to the full
  * summary output. If it can locate the submodule objects directory it will
  * attempt to lookup both the left and right commits and put them into the
@@ -1390,18 +1407,6 @@ int parallel_submodules(void)
 	return parallel_jobs;
 }
 
-void prepare_submodule_repo_env(struct argv_array *out)
-{
-	const char * const *var;
-
-	for (var = local_repo_env; *var; var++) {
-		if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
-			argv_array_push(out, *var);
-	}
-	argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
-			 DEFAULT_GIT_DIR_ENVIRONMENT);
-}
-
 /*
  * Embeds a single submodules git directory into the superprojects git dir,
  * non recursively.
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 12/17] update submodules: add submodule_move_head

[Stefan Beller]

In later patches we introduce the options and flag for commands
that modify the working directory, e.g. git-checkout.

This piece of code will be used universally for
all these working tree modifications as it
* supports dry run to answer the question:
  "Is it safe to change the submodule to this new state?"
  e.g. is it overwriting untracked files or are there local
  changes that would be overwritten?
* supports a force flag that can be used for resetting
  the tree.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 submodule.h |   7 ++++
 2 files changed, 142 insertions(+)

diff --git a/submodule.c b/submodule.c
index 0b2596e88a..bc5fecf8c5 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1239,6 +1239,141 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
 	return ret;
 }
 
+static int submodule_has_dirty_index(const struct submodule *sub)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	argv_array_pushl(&cp.args, "diff-index", "--quiet", \
+					"--cached", "HEAD", NULL);
+	cp.no_stdin = 1;
+	cp.no_stdout = 1;
+	cp.dir = sub->path;
+	if (start_command(&cp))
+		die("could not recurse into submodule '%s'", sub->path);
+
+	return finish_command(&cp);
+}
+
+static void submodule_reset_index(const char *path)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.dir = path;
+
+	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
+	argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
+
+	argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);
+
+	if (run_command(&cp))
+		die("could not reset submodule index");
+}
+
+/**
+ * Moves a submodule at a given path from a given head to another new head.
+ * For edge cases (a submodule coming into existence or removing a submodule)
+ * pass NULL for old or new respectively.
+ */
+int submodule_move_head(const char *path,
+			 const char *old,
+			 const char *new,
+			 unsigned flags)
+{
+	int ret = 0;
+	struct child_process cp = CHILD_PROCESS_INIT;
+	const struct submodule *sub;
+
+	sub = submodule_from_path(null_sha1, path);
+
+	if (!sub)
+		die("BUG: could not get submodule information for '%s'", path);
+
+	if (old && !(flags & SUBMODULE_MOVE_HEAD_FORCE)) {
+		/* Check if the submodule has a dirty index. */
+		if (submodule_has_dirty_index(sub))
+			return error(_("submodule '%s' has dirty index"), path);
+	}
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
+		if (old) {
+			if (!submodule_uses_gitfile(path))
+				absorb_git_dir_into_superproject("", path,
+					ABSORB_GITDIR_RECURSE_SUBMODULES);
+		} else {
+			struct strbuf sb = STRBUF_INIT;
+			strbuf_addf(&sb, "%s/modules/%s",
+				    get_git_common_dir(), sub->name);
+			connect_work_tree_and_git_dir(path, sb.buf);
+			strbuf_release(&sb);
+
+			/* make sure the index is clean as well */
+			submodule_reset_index(path);
+		}
+	}
+
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.dir = path;
+
+	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
+	argv_array_pushl(&cp.args, "read-tree", NULL);
+
+	if (flags & SUBMODULE_MOVE_HEAD_DRY_RUN)
+		argv_array_push(&cp.args, "-n");
+	else
+		argv_array_push(&cp.args, "-u");
+
+	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
+		argv_array_push(&cp.args, "--reset");
+	else
+		argv_array_push(&cp.args, "-m");
+
+	argv_array_push(&cp.args, old ? old : EMPTY_TREE_SHA1_HEX);
+	argv_array_push(&cp.args, new ? new : EMPTY_TREE_SHA1_HEX);
+
+	if (run_command(&cp)) {
+		ret = -1;
+		goto out;
+	}
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
+		if (new) {
+			struct child_process cp1 = CHILD_PROCESS_INIT;
+			/* also set the HEAD accordingly */
+			cp1.git_cmd = 1;
+			cp1.no_stdin = 1;
+			cp1.dir = path;
+
+			argv_array_pushl(&cp1.args, "update-ref", "HEAD",
+					 new ? new : EMPTY_TREE_SHA1_HEX, NULL);
+
+			if (run_command(&cp1)) {
+				ret = -1;
+				goto out;
+			}
+		} else {
+			struct strbuf sb = STRBUF_INIT;
+
+			strbuf_addf(&sb, "%s/.git", path);
+			unlink_or_warn(sb.buf);
+			strbuf_release(&sb);
+
+			if (is_empty_dir(path))
+				rmdir_or_warn(path);
+		}
+	}
+out:
+	return ret;
+}
+
 static int find_first_merges(struct object_array *result, const char *path,
 		struct commit *a, struct commit *b)
 {
diff --git a/submodule.h b/submodule.h
index 6f3fe85c7c..4cdf6445f7 100644
--- a/submodule.h
+++ b/submodule.h
@@ -96,6 +96,13 @@ extern int push_unpushed_submodules(struct sha1_array *commits,
 extern void connect_work_tree_and_git_dir(const char *work_tree, const char *git_dir);
 extern int parallel_submodules(void);
 
+#define SUBMODULE_MOVE_HEAD_DRY_RUN (1<<0)
+#define SUBMODULE_MOVE_HEAD_FORCE   (1<<1)
+extern int submodule_move_head(const char *path,
+			       const char *old,
+			       const char *new,
+			       unsigned flags);
+
 /*
  * Prepare the "env_array" parameter of a "struct child_process" for executing
  * a submodule by clearing any repo-specific envirionment variables, but
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 13/17] unpack-trees: pass old oid to verify_clean_submodule

[Stefan Beller]

The check (which uses the old oid) is yet to be implemented, but this part
is just a refactor, so it can go separately first.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 unpack-trees.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 3a8ee19fe8..616a0ae4b2 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1407,7 +1407,8 @@ static void invalidate_ce_path(const struct cache_entry *ce,
  * Currently, git does not checkout subprojects during a superproject
  * checkout, so it is not going to overwrite anything.
  */
-static int verify_clean_submodule(const struct cache_entry *ce,
+static int verify_clean_submodule(const char *old_sha1,
+				  const struct cache_entry *ce,
 				  enum unpack_trees_error_types error_type,
 				  struct unpack_trees_options *o)
 {
@@ -1427,16 +1428,18 @@ static int verify_clean_subdirectory(const struct cache_entry *ce,
 	struct dir_struct d;
 	char *pathbuf;
 	int cnt = 0;
-	unsigned char sha1[20];
 
-	if (S_ISGITLINK(ce->ce_mode) &&
-	    resolve_gitlink_ref(ce->name, "HEAD", sha1) == 0) {
-		/* If we are not going to update the submodule, then
+	if (S_ISGITLINK(ce->ce_mode)) {
+		unsigned char sha1[20];
+		int sub_head = resolve_gitlink_ref(ce->name, "HEAD", sha1);
+		/*
+		 * If we are not going to update the submodule, then
 		 * we don't care.
 		 */
-		if (!hashcmp(sha1, ce->oid.hash))
+		if (!sub_head && !hashcmp(sha1, ce->oid.hash))
 			return 0;
-		return verify_clean_submodule(ce, error_type, o);
+		return verify_clean_submodule(sub_head ? NULL : sha1_to_hex(sha1),
+					      ce, error_type, o);
 	}
 
 	/*
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 14/17] unpack-trees: check if we can perform the operation for submodules

[Stefan Beller]

In a later patch we'll support submodule entries to be
in sync with the tree in working tree changing commands,
such as checkout or read-tree.

When a new submodule entry changes in the tree, we need to
check if there are conflicts (directory/file conflicts)
for the tree. Add this check for submodules to be
performed before the working tree is touched.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 unpack-trees.c | 131 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
 unpack-trees.h |   1 +
 2 files changed, 123 insertions(+), 9 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 616a0ae4b2..8333da2cc9 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -10,6 +10,8 @@
 #include "attr.h"
 #include "split-index.h"
 #include "dir.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 /*
  * Error messages expected by scripts out of plumbing commands such as
@@ -45,6 +47,9 @@ static const char *unpack_plumbing_errors[NB_UNPACK_TREES_ERROR_TYPES] = {
 
 	/* ERROR_WOULD_LOSE_ORPHANED_REMOVED */
 	"Working tree file '%s' would be removed by sparse checkout update.",
+
+	/* ERROR_WOULD_LOSE_SUBMODULE */
+	"Submodule '%s' cannot checkout new HEAD.",
 };
 
 #define ERRORMSG(o,type) \
@@ -161,6 +166,8 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 		_("The following working tree files would be overwritten by sparse checkout update:\n%s");
 	msgs[ERROR_WOULD_LOSE_ORPHANED_REMOVED] =
 		_("The following working tree files would be removed by sparse checkout update:\n%s");
+	msgs[ERROR_WOULD_LOSE_SUBMODULE] =
+		_("Submodule '%s' cannot checkout new HEAD");
 
 	opts->show_all_errors = 1;
 	/* rejected paths may not have a static buffer */
@@ -240,12 +247,75 @@ static void display_error_msgs(struct unpack_trees_options *o)
 		fprintf(stderr, _("Aborting\n"));
 }
 
+static int check_submodule_move_head(const struct cache_entry *ce,
+				     const char *old_id,
+				     const char *new_id,
+				     struct unpack_trees_options *o)
+{
+	const struct submodule *sub = submodule_from_ce(ce);
+	if (!sub)
+		return 0;
+
+	switch (sub->update_strategy.type) {
+	case SM_UPDATE_UNSPECIFIED:
+	case SM_UPDATE_CHECKOUT:
+		if (submodule_move_head(ce->name, old_id, new_id, SUBMODULE_MOVE_HEAD_DRY_RUN))
+			return o->gently ? -1 :
+				add_rejected_path(o, ERROR_WOULD_LOSE_SUBMODULE, ce->name);
+		return 0;
+	case SM_UPDATE_NONE:
+		return 0;
+	case SM_UPDATE_REBASE:
+	case SM_UPDATE_MERGE:
+	case SM_UPDATE_COMMAND:
+	default:
+		warning(_("submodule update strategy not supported for submodule '%s'"), ce->name);
+		return -1;
+	}
+}
+
+static void reload_gitmodules_file(struct index_state *index,
+				   struct checkout *state)
+{
+	int i;
+	for (i = 0; i < index->cache_nr; i++) {
+		struct cache_entry *ce = index->cache[i];
+		if (ce->ce_flags & CE_UPDATE) {
+			int r = strcmp(ce->name, ".gitmodules");
+			if (r < 0)
+				continue;
+			else if (r == 0) {
+				submodule_free();
+				checkout_entry(ce, state, NULL);
+				gitmodules_config();
+				git_config(submodule_config, NULL);
+			} else
+				break;
+		}
+	}
+}
+
 /*
  * Unlink the last component and schedule the leading directories for
  * removal, such that empty directories get removed.
  */
 static void unlink_entry(const struct cache_entry *ce)
 {
+	const struct submodule *sub = submodule_from_ce(ce);
+	if (sub) {
+		switch (sub->update_strategy.type) {
+		case SM_UPDATE_UNSPECIFIED:
+		case SM_UPDATE_CHECKOUT:
+		case SM_UPDATE_REBASE:
+		case SM_UPDATE_MERGE:
+			submodule_move_head(ce->name, "HEAD", NULL,
+					    SUBMODULE_MOVE_HEAD_FORCE);
+			break;
+		case SM_UPDATE_NONE:
+		case SM_UPDATE_COMMAND:
+			return; /* Do not touch the submodule. */
+		}
+	}
 	if (!check_leading_path(ce->name, ce_namelen(ce)))
 		return;
 	if (remove_or_warn(ce->ce_mode, ce->name))
@@ -301,6 +371,9 @@ static int check_updates(struct unpack_trees_options *o)
 	remove_marked_cache_entries(index);
 	remove_scheduled_dirs();
 
+	if (should_update_submodules() && o->update && !o->dry_run)
+		reload_gitmodules_file(index, &state);
+
 	for (i = 0; i < index->cache_nr; i++) {
 		struct cache_entry *ce = index->cache[i];
 
@@ -1358,17 +1431,26 @@ static int verify_uptodate_1(const struct cache_entry *ce,
 	if (!lstat(ce->name, &st)) {
 		int flags = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE;
 		unsigned changed = ie_match_stat(o->src_index, ce, &st, flags);
+
+		if (submodule_from_ce(ce)) {
+			int r = check_submodule_move_head(ce,
+				"HEAD", oid_to_hex(&ce->oid), o);
+			if (r)
+				return o->gently ? -1 :
+					add_rejected_path(o, error_type, ce->name);
+			return 0;
+		}
+
 		if (!changed)
 			return 0;
 		/*
-		 * NEEDSWORK: the current default policy is to allow
-		 * submodule to be out of sync wrt the superproject
-		 * index.  This needs to be tightened later for
-		 * submodules that are marked to be automatically
-		 * checked out.
+		 * Historic default policy was to allow submodule to be out
+		 * of sync wrt the superproject index. If the submodule was
+		 * not considered interesting above, we don't care here.
 		 */
 		if (S_ISGITLINK(ce->ce_mode))
 			return 0;
+
 		errno = 0;
 	}
 	if (errno == ENOENT)
@@ -1412,7 +1494,11 @@ static int verify_clean_submodule(const char *old_sha1,
 				  enum unpack_trees_error_types error_type,
 				  struct unpack_trees_options *o)
 {
-	return 0;
+	if (!submodule_from_ce(ce))
+		return 0;
+
+	return check_submodule_move_head(ce, old_sha1,
+					 oid_to_hex(&ce->oid), o);
 }
 
 static int verify_clean_subdirectory(const struct cache_entry *ce,
@@ -1578,9 +1664,15 @@ static int verify_absent_1(const struct cache_entry *ce,
 		path = xmemdupz(ce->name, len);
 		if (lstat(path, &st))
 			ret = error_errno("cannot stat '%s'", path);
-		else
-			ret = check_ok_to_remove(path, len, DT_UNKNOWN, NULL,
-						 &st, error_type, o);
+		else {
+			if (submodule_from_ce(ce))
+				ret = check_submodule_move_head(ce,
+								oid_to_hex(&ce->oid),
+								NULL, o);
+			else
+				ret = check_ok_to_remove(path, len, DT_UNKNOWN, NULL,
+							 &st, error_type, o);
+		}
 		free(path);
 		return ret;
 	} else if (lstat(ce->name, &st)) {
@@ -1588,6 +1680,10 @@ static int verify_absent_1(const struct cache_entry *ce,
 			return error_errno("cannot stat '%s'", ce->name);
 		return 0;
 	} else {
+		if (submodule_from_ce(ce))
+			return check_submodule_move_head(ce, oid_to_hex(&ce->oid),
+							 NULL, o);
+
 		return check_ok_to_remove(ce->name, ce_namelen(ce),
 					  ce_to_dtype(ce), ce, &st,
 					  error_type, o);
@@ -1643,6 +1739,15 @@ static int merged_entry(const struct cache_entry *ce,
 			return -1;
 		}
 		invalidate_ce_path(merge, o);
+
+		if (submodule_from_ce(ce)) {
+			int ret = check_submodule_move_head(ce, NULL,
+							    oid_to_hex(&ce->oid),
+							    o);
+			if (ret)
+				return ret;
+		}
+
 	} else if (!(old->ce_flags & CE_CONFLICTED)) {
 		/*
 		 * See if we can re-use the old CE directly?
@@ -1663,6 +1768,14 @@ static int merged_entry(const struct cache_entry *ce,
 			update |= old->ce_flags & (CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
 			invalidate_ce_path(old, o);
 		}
+
+		if (submodule_from_ce(ce)) {
+			int ret = check_submodule_move_head(ce, oid_to_hex(&old->oid),
+							    oid_to_hex(&ce->oid),
+							    o);
+			if (ret)
+				return ret;
+		}
 	} else {
 		/*
 		 * Previously unmerged entry left as an existence
diff --git a/unpack-trees.h b/unpack-trees.h
index 36a73a6d00..6c48117b84 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -21,6 +21,7 @@ enum unpack_trees_error_types {
 	ERROR_SPARSE_NOT_UPTODATE_FILE,
 	ERROR_WOULD_LOSE_ORPHANED_OVERWRITTEN,
 	ERROR_WOULD_LOSE_ORPHANED_REMOVED,
+	ERROR_WOULD_LOSE_SUBMODULE,
 	NB_UNPACK_TREES_ERROR_TYPES
 };
 
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 15/17] entry.c: create submodules when interesting

[Stefan Beller]

When a submodule is introduced with a new revision
we need to create the submodule in the worktree as well.
As 'submodule_move_head' handles edge cases, all we have
to do is call it from within the function that creates
new files in the working tree for workingtree operations.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 entry.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/entry.c b/entry.c
index c6eea240b6..d2b512da90 100644
--- a/entry.c
+++ b/entry.c
@@ -2,6 +2,7 @@
 #include "blob.h"
 #include "dir.h"
 #include "streaming.h"
+#include "submodule.h"
 
 static void create_directories(const char *path, int path_len,
 			       const struct checkout *state)
@@ -146,6 +147,7 @@ static int write_entry(struct cache_entry *ce,
 	unsigned long size;
 	size_t wrote, newsize = 0;
 	struct stat st;
+	const struct submodule *sub;
 
 	if (ce_mode_s_ifmt == S_IFREG) {
 		struct stream_filter *filter = get_stream_filter(ce->name,
@@ -203,6 +205,10 @@ static int write_entry(struct cache_entry *ce,
 			return error("cannot create temporary submodule %s", path);
 		if (mkdir(path, 0777) < 0)
 			return error("cannot create submodule directory %s", path);
+		sub = submodule_from_ce(ce);
+		if (sub)
+			return submodule_move_head(ce->name,
+				NULL, oid_to_hex(&ce->oid), SUBMODULE_MOVE_HEAD_FORCE);
 		break;
 	default:
 		return error("unknown file mode for %s in index", path);
@@ -259,7 +265,31 @@ int checkout_entry(struct cache_entry *ce,
 	strbuf_add(&path, ce->name, ce_namelen(ce));
 
 	if (!check_path(path.buf, path.len, &st, state->base_dir_len)) {
+		const struct submodule *sub;
 		unsigned changed = ce_match_stat(ce, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
+		/*
+		 * Needs to be checked before !changed returns early,
+		 * as the possibly empty directory was not changed
+		 */
+		sub = submodule_from_ce(ce);
+		if (sub) {
+			int err;
+			if (!is_submodule_populated_gently(ce->name, &err)) {
+				struct stat sb;
+				if (lstat(ce->name, &sb))
+					die(_("could not stat file '%s'"), ce->name);
+				if (!(st.st_mode & S_IFDIR))
+					unlink_or_warn(ce->name);
+
+				return submodule_move_head(ce->name,
+					NULL, oid_to_hex(&ce->oid),
+					SUBMODULE_MOVE_HEAD_FORCE);
+			} else
+				return submodule_move_head(ce->name,
+					"HEAD", oid_to_hex(&ce->oid),
+					SUBMODULE_MOVE_HEAD_FORCE);
+		}
+
 		if (!changed)
 			return 0;
 		if (!state->force) {
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 16/17] builtin/checkout: add --recurse-submodules switch

[Stefan Beller]

This exposes a flag to recurse into submodules
in builtin/checkout making use of the code implemented
in prior patches.

A new failure mode is introduced in the submodule
update library, as the directory/submodule conflict
is not solved in prior patches.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/git-checkout.txt |  7 +++++++
 builtin/checkout.c             | 28 ++++++++++++++++++++++++++++
 t/lib-submodule-update.sh      | 23 +++++++++++++++++------
 t/t2013-checkout-submodule.sh  |  5 +++++
 4 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 8e2c0662dd..d6399c0af8 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -256,6 +256,13 @@ section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
 	out anyway. In other words, the ref can be held by more than one
 	worktree.
 
+--[no-]recurse-submodules::
+	Using --recurse-submodules will update the content of all initialized
+	submodules according to the commit recorded in the superproject. If
+	local modifications in a submodule would be overwritten the checkout
+	will fail unless `-f` is used. If nothing (or --no-recurse-submodules)
+	is used, the work trees of submodules will not be updated.
+
 <branch>::
 	Branch to checkout; if it refers to a branch (i.e., a name that,
 	when prepended with "refs/heads/", is a valid ref), then that
diff --git a/builtin/checkout.c b/builtin/checkout.c
index f174f50303..e9c5fcfaf8 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -21,12 +21,31 @@
 #include "submodule-config.h"
 #include "submodule.h"
 
+static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
+
 static const char * const checkout_usage[] = {
 	N_("git checkout [<options>] <branch>"),
 	N_("git checkout [<options>] [<branch>] -- <file>..."),
 	NULL,
 };
 
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
+{
+	if (unset) {
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
 struct checkout_opts {
 	int patch_mode;
 	int quiet;
@@ -1163,6 +1182,9 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 				N_("second guess 'git checkout <no-such-branch>'")),
 		OPT_BOOL(0, "ignore-other-worktrees", &opts.ignore_other_worktrees,
 			 N_("do not check if another worktree is holding the given ref")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules },
 		OPT_BOOL(0, "progress", &opts.show_progress, N_("force progress reporting")),
 		OPT_END(),
 	};
@@ -1193,6 +1215,12 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
 	}
 
+	if (recurse_submodules != RECURSE_SUBMODULES_OFF) {
+		git_config(submodule_config, NULL);
+		if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT)
+			set_config_update_recurse_submodules(recurse_submodules);
+	}
+
 	if ((!!opts.new_branch + !!opts.new_branch_force + !!opts.new_orphan_branch) > 1)
 		die(_("-b, -B and --orphan are mutually exclusive"));
 
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index deba618bee..0b659b530d 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -782,6 +782,11 @@ test_submodule_forced_switch () {
 
 test_submodule_switch_recursing () {
 	command="$1"
+	RESULT=success
+	if test "$KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS" = 1
+	then
+		RESULT=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -891,7 +896,7 @@ test_submodule_switch_recursing () {
 	'
 	# Replacing a submodule with files in a directory must succeeds
 	# when the submodule is clean
-	test_expect_success "$command: replace submodule with a directory" '
+	test_expect_$RESULT "$command: replace submodule with a directory" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -903,7 +908,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... absorbing a .git directory.
-	test_expect_success "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
+	test_expect_$RESULT "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -931,7 +936,7 @@ test_submodule_switch_recursing () {
 	'
 
 	# ... must check its local work tree for untracked files
-	test_expect_success "$command: replace submodule with a file must fail with untracked files" '
+	test_expect_$RESULT "$command: replace submodule with a file must fail with untracked files" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -987,7 +992,8 @@ test_submodule_switch_recursing () {
 		)
 	'
 
-	test_expect_success "$command: modified submodule updates submodule recursively" '
+	# recursing deeper than one level doesn't work yet.
+	test_expect_failure "$command: modified submodule updates submodule recursively" '
 		prolog &&
 		reset_work_tree_to_interested add_nested_sub &&
 		(
@@ -1006,6 +1012,11 @@ test_submodule_switch_recursing () {
 # the superproject as well as the submodule is allowed.
 test_submodule_forced_switch_recursing () {
 	command="$1"
+	RESULT=success
+	if test "$KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS" = 1
+	then
+		RESULT=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear creates empty dir ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -1100,7 +1111,7 @@ test_submodule_forced_switch_recursing () {
 		)
 	'
 	# Replacing a submodule with files in a directory ...
-	test_expect_success "$command: replace submodule with a directory" '
+	test_expect_$RESULT "$command: replace submodule with a directory" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -1151,7 +1162,7 @@ test_submodule_forced_switch_recursing () {
 	'
 
 	# ... but stops for untracked files that would be lost
-	test_expect_success "$command: replace submodule with a file" '
+	test_expect_$RESULT "$command: replace submodule with a file stops for untracked files" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
diff --git a/t/t2013-checkout-submodule.sh b/t/t2013-checkout-submodule.sh
index 6847f75822..aa35223369 100755
--- a/t/t2013-checkout-submodule.sh
+++ b/t/t2013-checkout-submodule.sh
@@ -63,6 +63,11 @@ test_expect_success '"checkout <submodule>" honors submodule.*.ignore from .git/
 	! test -s actual
 '
 
+KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+test_submodule_switch_recursing "git checkout --recurse-submodules"
+
+test_submodule_forced_switch_recursing "git checkout -f --recurse-submodules"
+
 test_submodule_switch "git checkout"
 
 test_submodule_forced_switch "git checkout -f"
-- 
2.12.0.rc1.45.g207f5fbb2b

[PATCH 17/17] builtin/read-tree: add --recurse-submodules switch

[Stefan Beller]

A new known failure mode is introduced[1], which is actually not
a failure but a feature in read-tree. Unlike checkout for which
the recursive submodule tests were originally written, read-tree does
warn about ignored untracked files that would be overwritten.
For the sake of keeping the test library for submodules generic, just
mark the test as a failure.

[1] KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/git-read-tree.txt |  6 ++++++
 builtin/read-tree.c             | 29 +++++++++++++++++++++++++++++
 t/lib-submodule-update.sh       |  7 ++++++-
 t/t1013-read-tree-submodule.sh  |  7 +++++++
 4 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt
index fa1d557e5b..ed9d63ef4a 100644
--- a/Documentation/git-read-tree.txt
+++ b/Documentation/git-read-tree.txt
@@ -115,6 +115,12 @@ OPTIONS
 	directories the index file and index output file are
 	located in.
 
+--[no-]recurse-submodules::
+	Using --recurse-submodules will update the content of all initialized
+	submodules according to the commit recorded in the superproject by
+	calling read-tree recursively, also setting the submodules HEAD to be
+	detached at that commit.
+
 --no-sparse-checkout::
 	Disable sparse checkout support even if `core.sparseCheckout`
 	is true.
diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 8ba64bc785..23e212ee8c 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -15,10 +15,13 @@
 #include "builtin.h"
 #include "parse-options.h"
 #include "resolve-undo.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 static int nr_trees;
 static int read_empty;
 static struct tree *trees[MAX_UNPACK_TREES];
+static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 
 static int list_tree(unsigned char *sha1)
 {
@@ -96,6 +99,23 @@ static int debug_merge(const struct cache_entry * const *stages,
 	return 0;
 }
 
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
+{
+	if (unset) {
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
 static struct lock_file lock_file;
 
 int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
@@ -137,6 +157,9 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 			 N_("skip applying sparse checkout filter")),
 		OPT_BOOL(0, "debug-unpack", &opts.debug_unpack,
 			 N_("debug unpack-trees")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules },
 		OPT_END()
 	};
 
@@ -152,6 +175,12 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 
 	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
 
+	if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT) {
+		gitmodules_config();
+		git_config(submodule_config, NULL);
+		set_config_update_recurse_submodules(RECURSE_SUBMODULES_ON);
+	}
+
 	prefix_set = opts.prefix ? 1 : 0;
 	if (1 < opts.merge + opts.reset + prefix_set)
 		die("Which one? -m, --reset, or --prefix?");
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 0b659b530d..e195b590a1 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -787,6 +787,11 @@ test_submodule_switch_recursing () {
 	then
 		RESULT=failure
 	fi
+	RESULT1=success
+	if test "$KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED" = 1
+	then
+		RESULT1=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -827,7 +832,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... but an ignored file is fine.
-	test_expect_success "$command: added submodule removes an untracked ignored file" '
+	test_expect_$RESULT1 "$command: added submodule removes an untracked ignored file" '
 		test_when_finished "rm submodule_update/.git/info/exclude" &&
 		prolog &&
 		reset_work_tree_to_interested no_submodule &&
diff --git a/t/t1013-read-tree-submodule.sh b/t/t1013-read-tree-submodule.sh
index 20526aed34..7019d0a04f 100755
--- a/t/t1013-read-tree-submodule.sh
+++ b/t/t1013-read-tree-submodule.sh
@@ -5,6 +5,13 @@ test_description='read-tree can handle submodules'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-submodule-update.sh
 
+KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED=1
+
+test_submodule_switch_recursing "git read-tree --recurse-submodules -u -m"
+
+test_submodule_forced_switch_recursing "git read-tree --recurse-submodules -u --reset"
+
 test_submodule_switch "git read-tree -u -m"
 
 test_submodule_forced_switch "git read-tree -u --reset"
-- 
2.12.0.rc1.45.g207f5fbb2b

Re: [PATCH 07/17] connect_work_tree_and_git_dir: safely create leading directories

[Brandon Williams]

On 03/09, Stefan Beller wrote:
> In a later patch we'll use connect_work_tree_and_git_dir when the
> directory for the gitlink file doesn't exist yet. This patch makes
> connect_work_tree_and_git_dir safe to use for both cases of
> either the git dir or the working dir missing.
> 
> To do so, we need to call safe_create_leading_directories[_const]
> on both directories. However this has to happen before we construct
> the absolute paths as real_pathdup assumes the directories to
> be there already.
> 
> So for both the config file in the git dir as well as the .git link
> file we need to
> a) construct the name
> b) call SCLD
> c) get the absolute path
> d) once a-c is done for both we can consume the absolute path
>    to compute the relative path to each other and store those
>    relative paths.
> 
> The implementation provided here puts a) and b) for both cases first,
> and then performs c and d after.
> 
> One of the two users of 'connect_work_tree_and_git_dir' already checked
> for the directory being there, so we can loose that check as
> connect_work_tree_and_git_dir handles this functionality now.
> 
> Signed-off-by: Stefan Beller <sbeller@google.com>
> ---
>  dir.c       | 32 +++++++++++++++++++++-----------
>  submodule.c | 11 ++---------
>  2 files changed, 23 insertions(+), 20 deletions(-)
> 
> diff --git a/dir.c b/dir.c
> index 4541f9e146..6f52af7abb 100644
> --- a/dir.c
> +++ b/dir.c
> @@ -2728,23 +2728,33 @@ void untracked_cache_add_to_index(struct index_state *istate,
>  /* Update gitfile and core.worktree setting to connect work tree and git dir */
>  void connect_work_tree_and_git_dir(const char *work_tree_, const char *git_dir_)
>  {
> -	struct strbuf file_name = STRBUF_INIT;
> +	struct strbuf gitfile_sb = STRBUF_INIT;
> +	struct strbuf cfg_sb = STRBUF_INIT;
>  	struct strbuf rel_path = STRBUF_INIT;
> -	char *git_dir = real_pathdup(git_dir_);
> -	char *work_tree = real_pathdup(work_tree_);
> +	char *git_dir, *work_tree;
>  
> -	/* Update gitfile */
> -	strbuf_addf(&file_name, "%s/.git", work_tree);
> -	write_file(file_name.buf, "gitdir: %s",
> -		   relative_path(git_dir, work_tree, &rel_path));
> +	/* Prepare .git file */
> +	strbuf_addf(&gitfile_sb, "%s/.git", work_tree_);
> +	if (safe_create_leading_directories_const(gitfile_sb.buf))
> +		die(_("could not create directories for %s"), gitfile_sb.buf);
> +
> +	/* Prepare config file */
> +	strbuf_addf(&cfg_sb, "%s/config", git_dir_);
> +	if (safe_create_leading_directories_const(cfg_sb.buf))
> +		die(_("could not create directories for %s"), cfg_sb.buf);
>  
> +	git_dir = real_pathdup(git_dir_);
> +	work_tree = real_pathdup(work_tree_);

Just a note that this is a spot that'll be affected by the change to
real_pathdup() which adds a 'die_on_error' parameter to correct bad
behaviour I introduced.

> +
> +	/* Write .git file */
> +	write_file(gitfile_sb.buf, "gitdir: %s",
> +		   relative_path(git_dir, work_tree, &rel_path));
>  	/* Update core.worktree setting */
> -	strbuf_reset(&file_name);
> -	strbuf_addf(&file_name, "%s/config", git_dir);
> -	git_config_set_in_file(file_name.buf, "core.worktree",
> +	git_config_set_in_file(cfg_sb.buf, "core.worktree",
>  			       relative_path(work_tree, git_dir, &rel_path));
>  
> -	strbuf_release(&file_name);
> +	strbuf_release(&gitfile_sb);
> +	strbuf_release(&cfg_sb);
>  	strbuf_release(&rel_path);
>  	free(work_tree);
>  	free(git_dir);
> diff --git a/submodule.c b/submodule.c
> index 0e55372f37..04d185738f 100644
> --- a/submodule.c
> +++ b/submodule.c
> @@ -1442,8 +1442,6 @@ void absorb_git_dir_into_superproject(const char *prefix,
>  
>  	/* Not populated? */
>  	if (!sub_git_dir) {
> -		char *real_new_git_dir;
> -		const char *new_git_dir;
>  		const struct submodule *sub;
>  
>  		if (err_code == READ_GITFILE_ERR_STAT_FAILED) {
> @@ -1466,13 +1464,8 @@ void absorb_git_dir_into_superproject(const char *prefix,
>  		sub = submodule_from_path(null_sha1, path);
>  		if (!sub)
>  			die(_("could not lookup name for submodule '%s'"), path);
> -		new_git_dir = git_path("modules/%s", sub->name);
> -		if (safe_create_leading_directories_const(new_git_dir) < 0)
> -			die(_("could not create directory '%s'"), new_git_dir);
> -		real_new_git_dir = real_pathdup(new_git_dir);
> -		connect_work_tree_and_git_dir(path, real_new_git_dir);
> -
> -		free(real_new_git_dir);
> +		connect_work_tree_and_git_dir(path,
> +			git_path("modules/%s", sub->name));
>  	} else {
>  		/* Is it already absorbed into the superprojects git dir? */
>  		char *real_sub_git_dir = real_pathdup(sub_git_dir);
> -- 
> 2.12.0.rc1.45.g207f5fbb2b
> 

-- 
Brandon Williams

Re: [PATCH 12/17] update submodules: add submodule_move_head

[Brandon Williams]

On 03/09, Stefan Beller wrote:
> In later patches we introduce the options and flag for commands
> that modify the working directory, e.g. git-checkout.
> 
> This piece of code will be used universally for
> all these working tree modifications as it
> * supports dry run to answer the question:
>   "Is it safe to change the submodule to this new state?"
>   e.g. is it overwriting untracked files or are there local
>   changes that would be overwritten?
> * supports a force flag that can be used for resetting
>   the tree.
> 
> Signed-off-by: Stefan Beller <sbeller@google.com>
> ---
>  submodule.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  submodule.h |   7 ++++
>  2 files changed, 142 insertions(+)
> 
> diff --git a/submodule.c b/submodule.c
> index 0b2596e88a..bc5fecf8c5 100644
> --- a/submodule.c
> +++ b/submodule.c
> @@ -1239,6 +1239,141 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
>  	return ret;
>  }
>  
> +static int submodule_has_dirty_index(const struct submodule *sub)
> +{
> +	struct child_process cp = CHILD_PROCESS_INIT;
> +
> +	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
> +
> +	cp.git_cmd = 1;
> +	argv_array_pushl(&cp.args, "diff-index", "--quiet", \
> +					"--cached", "HEAD", NULL);

The formatting of this line is a little odd.  Also you can drop the
backslash.

Mostly because I haven't dug too deep yet/can't remember: Does
diff-index do the correct thing with nested submodules?  If I remember
correctly it does so this shouldn't be a problem.

> +	cp.no_stdin = 1;
> +	cp.no_stdout = 1;
> +	cp.dir = sub->path;
> +	if (start_command(&cp))
> +		die("could not recurse into submodule '%s'", sub->path);
> +
> +	return finish_command(&cp);
> +}
> +
> +static void submodule_reset_index(const char *path)
> +{
> +	struct child_process cp = CHILD_PROCESS_INIT;
> +	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
> +
> +	cp.git_cmd = 1;
> +	cp.no_stdin = 1;
> +	cp.dir = path;
> +
> +	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
> +	argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
> +
> +	argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);
> +
> +	if (run_command(&cp))
> +		die("could not reset submodule index");
> +}
> +
> +/**
> + * Moves a submodule at a given path from a given head to another new head.
> + * For edge cases (a submodule coming into existence or removing a submodule)
> + * pass NULL for old or new respectively.
> + */
> +int submodule_move_head(const char *path,
> +			 const char *old,
> +			 const char *new,
> +			 unsigned flags)
> +{
> +	int ret = 0;
> +	struct child_process cp = CHILD_PROCESS_INIT;
> +	const struct submodule *sub;
> +
> +	sub = submodule_from_path(null_sha1, path);
> +
> +	if (!sub)
> +		die("BUG: could not get submodule information for '%s'", path);
> +
> +	if (old && !(flags & SUBMODULE_MOVE_HEAD_FORCE)) {
> +		/* Check if the submodule has a dirty index. */
> +		if (submodule_has_dirty_index(sub))
> +			return error(_("submodule '%s' has dirty index"), path);
> +	}
> +
> +	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
> +		if (old) {
> +			if (!submodule_uses_gitfile(path))
> +				absorb_git_dir_into_superproject("", path,
> +					ABSORB_GITDIR_RECURSE_SUBMODULES);
> +		} else {
> +			struct strbuf sb = STRBUF_INIT;
> +			strbuf_addf(&sb, "%s/modules/%s",
> +				    get_git_common_dir(), sub->name);
> +			connect_work_tree_and_git_dir(path, sb.buf);
> +			strbuf_release(&sb);
> +
> +			/* make sure the index is clean as well */
> +			submodule_reset_index(path);
> +		}
> +	}
> +
> +	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
> +
> +	cp.git_cmd = 1;
> +	cp.no_stdin = 1;
> +	cp.dir = path;
> +
> +	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
> +	argv_array_pushl(&cp.args, "read-tree", NULL);
> +
> +	if (flags & SUBMODULE_MOVE_HEAD_DRY_RUN)
> +		argv_array_push(&cp.args, "-n");
> +	else
> +		argv_array_push(&cp.args, "-u");
> +
> +	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
> +		argv_array_push(&cp.args, "--reset");
> +	else
> +		argv_array_push(&cp.args, "-m");
> +
> +	argv_array_push(&cp.args, old ? old : EMPTY_TREE_SHA1_HEX);
> +	argv_array_push(&cp.args, new ? new : EMPTY_TREE_SHA1_HEX);
> +
> +	if (run_command(&cp)) {
> +		ret = -1;
> +		goto out;
> +	}
> +
> +	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
> +		if (new) {
> +			struct child_process cp1 = CHILD_PROCESS_INIT;
> +			/* also set the HEAD accordingly */
> +			cp1.git_cmd = 1;
> +			cp1.no_stdin = 1;
> +			cp1.dir = path;
> +
> +			argv_array_pushl(&cp1.args, "update-ref", "HEAD",
> +					 new ? new : EMPTY_TREE_SHA1_HEX, NULL);
> +
> +			if (run_command(&cp1)) {
> +				ret = -1;
> +				goto out;
> +			}
> +		} else {
> +			struct strbuf sb = STRBUF_INIT;
> +
> +			strbuf_addf(&sb, "%s/.git", path);
> +			unlink_or_warn(sb.buf);
> +			strbuf_release(&sb);
> +
> +			if (is_empty_dir(path))
> +				rmdir_or_warn(path);
> +		}
> +	}
> +out:
> +	return ret;
> +}
> +
>  static int find_first_merges(struct object_array *result, const char *path,
>  		struct commit *a, struct commit *b)
>  {
> diff --git a/submodule.h b/submodule.h
> index 6f3fe85c7c..4cdf6445f7 100644
> --- a/submodule.h
> +++ b/submodule.h
> @@ -96,6 +96,13 @@ extern int push_unpushed_submodules(struct sha1_array *commits,
>  extern void connect_work_tree_and_git_dir(const char *work_tree, const char *git_dir);
>  extern int parallel_submodules(void);
>  
> +#define SUBMODULE_MOVE_HEAD_DRY_RUN (1<<0)
> +#define SUBMODULE_MOVE_HEAD_FORCE   (1<<1)
> +extern int submodule_move_head(const char *path,
> +			       const char *old,
> +			       const char *new,
> +			       unsigned flags);
> +
>  /*
>   * Prepare the "env_array" parameter of a "struct child_process" for executing
>   * a submodule by clearing any repo-specific envirionment variables, but
> -- 
> 2.12.0.rc1.45.g207f5fbb2b
> 

-- 
Brandon Williams

Re: [PATCH 12/17] update submodules: add submodule_move_head

[Brandon Williams]

On 03/09, Stefan Beller wrote:
> +static void submodule_reset_index(const char *path)
> +{
> +	struct child_process cp = CHILD_PROCESS_INIT;
> +	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
> +
> +	cp.git_cmd = 1;
> +	cp.no_stdin = 1;
> +	cp.dir = path;
> +
> +	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);

What happens with nested submodules? As in can we reach this code path
with super_prefix already being set?  If so we would need to include
that as part of the super_prefix being passed to the child.  Just
looking for some clarification.

> +	argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
> +
> +	argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);
> +
> +	if (run_command(&cp))
> +		die("could not reset submodule index");
> +}
> +

-- 
Brandon Williams

Re: [PATCH 12/17] update submodules: add submodule_move_head

[Brandon Williams]

On 03/09, Stefan Beller wrote:
> +/**
> + * Moves a submodule at a given path from a given head to another new head.
> + * For edge cases (a submodule coming into existence or removing a submodule)
> + * pass NULL for old or new respectively.
> + */
> +int submodule_move_head(const char *path,
> +			 const char *old,
> +			 const char *new,
> +			 unsigned flags)
> +{
> +	int ret = 0;
> +	struct child_process cp = CHILD_PROCESS_INIT;
> +	const struct submodule *sub;
> +
> +	sub = submodule_from_path(null_sha1, path);
> +
> +	if (!sub)
> +		die("BUG: could not get submodule information for '%s'", path);
> +
> +	if (old && !(flags & SUBMODULE_MOVE_HEAD_FORCE)) {
> +		/* Check if the submodule has a dirty index. */
> +		if (submodule_has_dirty_index(sub))
> +			return error(_("submodule '%s' has dirty index"), path);
> +	}
> +
> +	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
> +		if (old) {
> +			if (!submodule_uses_gitfile(path))
> +				absorb_git_dir_into_superproject("", path,
> +					ABSORB_GITDIR_RECURSE_SUBMODULES);
> +		} else {
> +			struct strbuf sb = STRBUF_INIT;
> +			strbuf_addf(&sb, "%s/modules/%s",
> +				    get_git_common_dir(), sub->name);
> +			connect_work_tree_and_git_dir(path, sb.buf);
> +			strbuf_release(&sb);
> +
> +			/* make sure the index is clean as well */
> +			submodule_reset_index(path);
> +		}
> +	}
> +
> +	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
> +
> +	cp.git_cmd = 1;
> +	cp.no_stdin = 1;
> +	cp.dir = path;
> +
> +	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);

Missed this one too.  Same question as the other spot.


-- 
Brandon Williams

Re: [PATCH 07/17] connect_work_tree_and_git_dir: safely create leading directories

[Junio C Hamano]

Brandon Williams <bmwill@google.com> writes:

>> +	git_dir = real_pathdup(git_dir_);
>> +	work_tree = real_pathdup(work_tree_);
>
> Just a note that this is a spot that'll be affected by the change to
> real_pathdup() which adds a 'die_on_error' parameter to correct bad
> behaviour I introduced.

Thanks for a reminder.  I _think_ I resolved this correctly when I
replaced the previous one with this round to re-queue on 'pu'.

Re: [PATCH 12/17] update submodules: add submodule_move_head

[Junio C Hamano]

Brandon Williams <bmwill@google.com> writes:

>> diff --git a/submodule.c b/submodule.c
>> index 0b2596e88a..bc5fecf8c5 100644
>> --- a/submodule.c
>> +++ b/submodule.c
>> @@ -1239,6 +1239,141 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
>>  	return ret;
>>  }
>>  
>> +static int submodule_has_dirty_index(const struct submodule *sub)
>> +{
>> +	struct child_process cp = CHILD_PROCESS_INIT;
>> +
>> +	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
>> +
>> +	cp.git_cmd = 1;
>> +	argv_array_pushl(&cp.args, "diff-index", "--quiet", \
>> +					"--cached", "HEAD", NULL);
>
> The formatting of this line is a little odd.  Also you can drop the
> backslash.

Heh.  I think I saw and pointed out the same during the review of
the previous round X-<.  It is a bit disappointing.

>> +static void submodule_reset_index(const char *path)
>> +{
>> +	struct child_process cp = CHILD_PROCESS_INIT;
>> +	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
>> +
>> +	cp.git_cmd = 1;
>> +	cp.no_stdin = 1;
>> +	cp.dir = path;
>> +
>> +	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
>> +	argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
>> +
>> +	argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);

Somewhat related; will this use of --super-prefix be affected when
we split it into two for "adjust pathspec" prefix and "adjust
output" prefix?

Re: [PATCH 12/17] update submodules: add submodule_move_head

[Brandon Williams]

On 03/11, Junio C Hamano wrote:
> Brandon Williams <bmwill@google.com> writes:
> 
> >> diff --git a/submodule.c b/submodule.c
> >> index 0b2596e88a..bc5fecf8c5 100644
> >> --- a/submodule.c
> >> +++ b/submodule.c
> >> @@ -1239,6 +1239,141 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
> >>  	return ret;
> >>  }
> >>  
> >> +static int submodule_has_dirty_index(const struct submodule *sub)
> >> +{
> >> +	struct child_process cp = CHILD_PROCESS_INIT;
> >> +
> >> +	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
> >> +
> >> +	cp.git_cmd = 1;
> >> +	argv_array_pushl(&cp.args, "diff-index", "--quiet", \
> >> +					"--cached", "HEAD", NULL);
> >
> > The formatting of this line is a little odd.  Also you can drop the
> > backslash.
> 
> Heh.  I think I saw and pointed out the same during the review of
> the previous round X-<.  It is a bit disappointing.
> 
> >> +static void submodule_reset_index(const char *path)
> >> +{
> >> +	struct child_process cp = CHILD_PROCESS_INIT;
> >> +	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
> >> +
> >> +	cp.git_cmd = 1;
> >> +	cp.no_stdin = 1;
> >> +	cp.dir = path;
> >> +
> >> +	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
> >> +	argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
> >> +
> >> +	argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);
> 
> Somewhat related; will this use of --super-prefix be affected when
> we split it into two for "adjust pathspec" prefix and "adjust
> output" prefix?

Maybe? From what we discussed we can have 'super_prefix' maintain its
current meaning (Path from root of parent down to the submodule) while
adding a new env var or option to pass the 'prefix' variable to the
child process (Path from root of parent to the directory the original
cmd was executed in).

So this shouldn't be affected unless we decide to change the semantics
of 'super_prefix'.

And I'm always torn on how best to do naming for the newer
functionality.  I think the easiest thing to do would be to have a
--prefix option to pass the 'prefix' from one process to the next, but
I'm sure there are other opinions on the matter.

-- 
Brandon Williams

Re: [PATCH 12/17] update submodules: add submodule_move_head

[Stefan Beller]

On Sat, Mar 11, 2017 at 11:09 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Brandon Williams <bmwill@google.com> writes:
>
>>> diff --git a/submodule.c b/submodule.c
>>> index 0b2596e88a..bc5fecf8c5 100644
>>> --- a/submodule.c
>>> +++ b/submodule.c
>>> @@ -1239,6 +1239,141 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
>>>      return ret;
>>>  }
>>>
>>> +static int submodule_has_dirty_index(const struct submodule *sub)
>>> +{
>>> +    struct child_process cp = CHILD_PROCESS_INIT;
>>> +
>>> +    prepare_submodule_repo_env_no_git_dir(&cp.env_array);
>>> +
>>> +    cp.git_cmd = 1;
>>> +    argv_array_pushl(&cp.args, "diff-index", "--quiet", \
>>> +                                    "--cached", "HEAD", NULL);
>>
>> The formatting of this line is a little odd.  Also you can drop the
>> backslash.
>
> Heh.  I think I saw and pointed out the same during the review of
> the previous round X-<.  It is a bit disappointing.

Yes. I remember having a local mixup of branches, such that I
fear I may have missed other feedback of the previous round as
well then. I do remember removing a backslash, so maybe I
got confused with another backslash as well.

I'll reroll with this fixed.

>
>>> +static void submodule_reset_index(const char *path)
>>> +{
>>> +    struct child_process cp = CHILD_PROCESS_INIT;
>>> +    prepare_submodule_repo_env_no_git_dir(&cp.env_array);
>>> +
>>> +    cp.git_cmd = 1;
>>> +    cp.no_stdin = 1;
>>> +    cp.dir = path;
>>> +
>>> +    argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
>>> +    argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
>>> +
>>> +    argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);
>
> Somewhat related; will this use of --super-prefix be affected when
> we split it into two for "adjust pathspec" prefix and "adjust
> output" prefix?

Let's see how the superproject prefixing evolves and what Brandon
sends out. When the superprefix changes its meaning I'll adjust here.

[PATCHv9 00/19] Checkout aware of Submodules!

[Stefan Beller]

previous work:
https://public-inbox.org/git/20170309221543.15897-1-sbeller@google.com/

v9:
 * inderdiff to current origin/sb/checkout-recurse-submodules below
 * fixed a '\' that was violating the style guide.
 * reordered the patches, such that
   -> the first two patches are Valerys series and could go on its own as
      a cleanup  
   -> added a new patch "submodule.c: get_super_prefix_or_empty" to
      have cleaner code.
 * split up the error conditions in the test lib for readability

v1..v8: see description in link to previous work above.

Thanks,
Stefan

diff --git a/submodule.c b/submodule.c
index bc5fecf8c5..929fc7bf04 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1239,6 +1239,14 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
 	return ret;
 }
 
+static const char *get_super_prefix_or_empty()
+{
+	const char *s = get_super_prefix();
+	if (!s)
+		s = "";
+	return s;
+}
+
 static int submodule_has_dirty_index(const struct submodule *sub)
 {
 	struct child_process cp = CHILD_PROCESS_INIT;
@@ -1246,8 +1254,8 @@ static int submodule_has_dirty_index(const struct submodule *sub)
 	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
 
 	cp.git_cmd = 1;
-	argv_array_pushl(&cp.args, "diff-index", "--quiet", \
-					"--cached", "HEAD", NULL);
+	argv_array_pushl(&cp.args, "diff-index", "--quiet",
+				   "--cached", "HEAD", NULL);
 	cp.no_stdin = 1;
 	cp.no_stdout = 1;
 	cp.dir = sub->path;
@@ -1266,7 +1274,8 @@ static void submodule_reset_index(const char *path)
 	cp.no_stdin = 1;
 	cp.dir = path;
 
-	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
+	argv_array_pushf(&cp.args, "--super-prefix=%s%s/",
+				   get_super_prefix_or_empty(), path);
 	argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
 
 	argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);
@@ -1323,7 +1332,8 @@ int submodule_move_head(const char *path,
 	cp.no_stdin = 1;
 	cp.dir = path;
 
-	argv_array_pushf(&cp.args, "--super-prefix=%s/", path);
+	argv_array_pushf(&cp.args, "--super-prefix=%s%s/",
+			get_super_prefix_or_empty(), path);
 	argv_array_pushl(&cp.args, "read-tree", NULL);
 
 	if (flags & SUBMODULE_MOVE_HEAD_DRY_RUN)
@@ -1573,11 +1583,8 @@ static void relocate_single_git_dir_into_superproject(const char *prefix,
 		die(_("could not create directory '%s'"), new_git_dir);
 	real_new_git_dir = real_pathdup(new_git_dir);
 
-	if (!prefix)
-		prefix = get_super_prefix();
-
 	fprintf(stderr, _("Migrating git directory of '%s%s' from\n'%s' to\n'%s'\n"),
-		prefix ? prefix : "", path,
+		get_super_prefix_or_empty(), path,
 		real_old_git_dir, real_new_git_dir);
 
 	relocate_gitdir(path, real_old_git_dir, real_new_git_dir);
@@ -1648,8 +1655,7 @@ void absorb_git_dir_into_superproject(const char *prefix,
 		if (flags & ~ABSORB_GITDIR_RECURSE_SUBMODULES)
 			die("BUG: we don't know how to pass the flags down?");
 
-		if (get_super_prefix())
-			strbuf_addstr(&sb, get_super_prefix());
+		strbuf_addstr(&sb, get_super_prefix_or_empty());
 		strbuf_addstr(&sb, path);
 		strbuf_addch(&sb, '/');
 
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index e195b590a1..fb4f7b014e 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -782,15 +782,20 @@ test_submodule_forced_switch () {
 
 test_submodule_switch_recursing () {
 	command="$1"
-	RESULT=success
+	RESULTDS=success
 	if test "$KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS" = 1
 	then
-		RESULT=failure
+		RESULTDS=failure
+	fi
+	RESULTR=success
+	if test "$KNOWN_FAILURE_SUBMODULE_RECURSIVE_NESTED" = 1
+	then
+		RESULTR=failure
 	fi
-	RESULT1=success
+	RESULTOI=success
 	if test "$KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED" = 1
 	then
-		RESULT1=failure
+		RESULTOI=failure
 	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
@@ -832,7 +837,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... but an ignored file is fine.
-	test_expect_$RESULT1 "$command: added submodule removes an untracked ignored file" '
+	test_expect_$RESULTOI "$command: added submodule removes an untracked ignored file" '
 		test_when_finished "rm submodule_update/.git/info/exclude" &&
 		prolog &&
 		reset_work_tree_to_interested no_submodule &&
@@ -901,7 +906,7 @@ test_submodule_switch_recursing () {
 	'
 	# Replacing a submodule with files in a directory must succeeds
 	# when the submodule is clean
-	test_expect_$RESULT "$command: replace submodule with a directory" '
+	test_expect_$RESULTDS "$command: replace submodule with a directory" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -913,7 +918,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... absorbing a .git directory.
-	test_expect_$RESULT "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
+	test_expect_$RESULTDS "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -941,7 +946,7 @@ test_submodule_switch_recursing () {
 	'
 
 	# ... must check its local work tree for untracked files
-	test_expect_$RESULT "$command: replace submodule with a file must fail with untracked files" '
+	test_expect_$RESULTDS "$command: replace submodule with a file must fail with untracked files" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -998,7 +1003,7 @@ test_submodule_switch_recursing () {
 	'
 
 	# recursing deeper than one level doesn't work yet.
-	test_expect_failure "$command: modified submodule updates submodule recursively" '
+	test_expect_$RESULTR "$command: modified submodule updates submodule recursively" '
 		prolog &&
 		reset_work_tree_to_interested add_nested_sub &&
 		(
@@ -1116,13 +1121,13 @@ test_submodule_forced_switch_recursing () {
 		)
 	'
 	# Replacing a submodule with files in a directory ...
-	test_expect_$RESULT "$command: replace submodule with a directory" '
+	test_expect_success "$command: replace submodule with a directory" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
 			cd submodule_update &&
 			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
-			test_must_fail $command replace_sub1_with_directory &&
+			$command replace_sub1_with_directory &&
 			test_superproject_content origin/replace_sub1_with_directory
 		)
 	'
diff --git a/t/t1013-read-tree-submodule.sh b/t/t1013-read-tree-submodule.sh
index 7019d0a04f..de1ba02dc5 100755
--- a/t/t1013-read-tree-submodule.sh
+++ b/t/t1013-read-tree-submodule.sh
@@ -5,6 +5,7 @@ test_description='read-tree can handle submodules'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-submodule-update.sh
 
+KNOWN_FAILURE_SUBMODULE_RECURSIVE_NESTED=1
 KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
 KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED=1
 
diff --git a/t/t2013-checkout-submodule.sh b/t/t2013-checkout-submodule.sh
index aa35223369..e8f70b806f 100755
--- a/t/t2013-checkout-submodule.sh
+++ b/t/t2013-checkout-submodule.sh
@@ -64,6 +64,7 @@ test_expect_success '"checkout <submodule>" honors submodule.*.ignore from .git/
 '
 
 KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+KNOWN_FAILURE_SUBMODULE_RECURSIVE_NESTED=1
 test_submodule_switch_recursing "git checkout --recurse-submodules"
 
 test_submodule_forced_switch_recursing "git checkout -f --recurse-submodules"

[PATCH 01/19] connect_work_tree_and_git_dir: safely create leading directories

[Stefan Beller]

In a later patch we'll use connect_work_tree_and_git_dir when the
directory for the gitlink file doesn't exist yet. This patch makes
connect_work_tree_and_git_dir safe to use for both cases of
either the git dir or the working dir missing.

To do so, we need to call safe_create_leading_directories[_const]
on both directories. However this has to happen before we construct
the absolute paths as real_pathdup assumes the directories to
be there already.

So for both the config file in the git dir as well as the .git link
file we need to
a) construct the name
b) call SCLD
c) get the absolute path
d) once a-c is done for both we can consume the absolute path
   to compute the relative path to each other and store those
   relative paths.

The implementation provided here puts a) and b) for both cases first,
and then performs c and d after.

One of the two users of 'connect_work_tree_and_git_dir' already checked
for the directory being there, so we can loose that check as
connect_work_tree_and_git_dir handles this functionality now.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 dir.c       | 32 +++++++++++++++++++++-----------
 submodule.c | 11 ++---------
 2 files changed, 23 insertions(+), 20 deletions(-)

diff --git a/dir.c b/dir.c
index 4541f9e146..6f52af7abb 100644
--- a/dir.c
+++ b/dir.c
@@ -2728,23 +2728,33 @@ void untracked_cache_add_to_index(struct index_state *istate,
 /* Update gitfile and core.worktree setting to connect work tree and git dir */
 void connect_work_tree_and_git_dir(const char *work_tree_, const char *git_dir_)
 {
-	struct strbuf file_name = STRBUF_INIT;
+	struct strbuf gitfile_sb = STRBUF_INIT;
+	struct strbuf cfg_sb = STRBUF_INIT;
 	struct strbuf rel_path = STRBUF_INIT;
-	char *git_dir = real_pathdup(git_dir_);
-	char *work_tree = real_pathdup(work_tree_);
+	char *git_dir, *work_tree;
 
-	/* Update gitfile */
-	strbuf_addf(&file_name, "%s/.git", work_tree);
-	write_file(file_name.buf, "gitdir: %s",
-		   relative_path(git_dir, work_tree, &rel_path));
+	/* Prepare .git file */
+	strbuf_addf(&gitfile_sb, "%s/.git", work_tree_);
+	if (safe_create_leading_directories_const(gitfile_sb.buf))
+		die(_("could not create directories for %s"), gitfile_sb.buf);
+
+	/* Prepare config file */
+	strbuf_addf(&cfg_sb, "%s/config", git_dir_);
+	if (safe_create_leading_directories_const(cfg_sb.buf))
+		die(_("could not create directories for %s"), cfg_sb.buf);
 
+	git_dir = real_pathdup(git_dir_);
+	work_tree = real_pathdup(work_tree_);
+
+	/* Write .git file */
+	write_file(gitfile_sb.buf, "gitdir: %s",
+		   relative_path(git_dir, work_tree, &rel_path));
 	/* Update core.worktree setting */
-	strbuf_reset(&file_name);
-	strbuf_addf(&file_name, "%s/config", git_dir);
-	git_config_set_in_file(file_name.buf, "core.worktree",
+	git_config_set_in_file(cfg_sb.buf, "core.worktree",
 			       relative_path(work_tree, git_dir, &rel_path));
 
-	strbuf_release(&file_name);
+	strbuf_release(&gitfile_sb);
+	strbuf_release(&cfg_sb);
 	strbuf_release(&rel_path);
 	free(work_tree);
 	free(git_dir);
diff --git a/submodule.c b/submodule.c
index 3b98766a6b..45e93a1d55 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1445,8 +1445,6 @@ void absorb_git_dir_into_superproject(const char *prefix,
 
 	/* Not populated? */
 	if (!sub_git_dir) {
-		char *real_new_git_dir;
-		const char *new_git_dir;
 		const struct submodule *sub;
 
 		if (err_code == READ_GITFILE_ERR_STAT_FAILED) {
@@ -1469,13 +1467,8 @@ void absorb_git_dir_into_superproject(const char *prefix,
 		sub = submodule_from_path(null_sha1, path);
 		if (!sub)
 			die(_("could not lookup name for submodule '%s'"), path);
-		new_git_dir = git_path("modules/%s", sub->name);
-		if (safe_create_leading_directories_const(new_git_dir) < 0)
-			die(_("could not create directory '%s'"), new_git_dir);
-		real_new_git_dir = real_pathdup(new_git_dir);
-		connect_work_tree_and_git_dir(path, real_new_git_dir);
-
-		free(real_new_git_dir);
+		connect_work_tree_and_git_dir(path,
+			git_path("modules/%s", sub->name));
 	} else {
 		/* Is it already absorbed into the superprojects git dir? */
 		char *real_sub_git_dir = real_pathdup(sub_git_dir);
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 02/19] submodule--helper.c: remove duplicate code

[Stefan Beller]

From: Valery Tolstov <me@vtolstov.org>

Remove code fragment from module_clone that duplicates functionality
of connect_work_tree_and_git_dir in dir.c

Signed-off-by: Valery Tolstov <me@vtolstov.org>
Reviewed-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/submodule--helper.c | 22 ++--------------------
 1 file changed, 2 insertions(+), 20 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 899dc334e3..86bafe1660 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -579,9 +579,7 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 	const char *name = NULL, *url = NULL, *depth = NULL;
 	int quiet = 0;
 	int progress = 0;
-	FILE *submodule_dot_git;
 	char *p, *path = NULL, *sm_gitdir;
-	struct strbuf rel_path = STRBUF_INIT;
 	struct strbuf sb = STRBUF_INIT;
 	struct string_list reference = STRING_LIST_INIT_NODUP;
 	char *sm_alternate = NULL, *error_strategy = NULL;
@@ -653,27 +651,12 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 		strbuf_reset(&sb);
 	}
 
-	/* Write a .git file in the submodule to redirect to the superproject. */
-	strbuf_addf(&sb, "%s/.git", path);
-	if (safe_create_leading_directories_const(sb.buf) < 0)
-		die(_("could not create leading directories of '%s'"), sb.buf);
-	submodule_dot_git = fopen(sb.buf, "w");
-	if (!submodule_dot_git)
-		die_errno(_("cannot open file '%s'"), sb.buf);
-
-	fprintf_or_die(submodule_dot_git, "gitdir: %s\n",
-		       relative_path(sm_gitdir, path, &rel_path));
-	if (fclose(submodule_dot_git))
-		die(_("could not close file %s"), sb.buf);
-	strbuf_reset(&sb);
-	strbuf_reset(&rel_path);
+	/* Connect module worktree and git dir */
+	connect_work_tree_and_git_dir(path, sm_gitdir);
 
-	/* Redirect the worktree of the submodule in the superproject's config */
 	p = git_pathdup_submodule(path, "config");
 	if (!p)
 		die(_("could not get submodule directory for '%s'"), path);
-	git_config_set_in_file(p, "core.worktree",
-			       relative_path(path, sm_gitdir, &rel_path));
 
 	/* setup alternateLocation and alternateErrorStrategy in the cloned submodule if needed */
 	git_config_get_string("submodule.alternateLocation", &sm_alternate);
@@ -689,7 +672,6 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 	free(error_strategy);
 
 	strbuf_release(&sb);
-	strbuf_release(&rel_path);
 	free(sm_gitdir);
 	free(path);
 	free(p);
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 03/19] lib-submodule-update.sh: reorder create_lib_submodule_repo

[Stefan Beller]

Redraw the ASCII art describing the setup using more space, such that
it is easier to understand.  The leaf commits are now ordered the same
way the actual code is ordered.

Add empty lines to the setup code separating each of the leaf commits,
each starting with a "checkout -b".

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 49 ++++++++++++++++++++++++++++-------------------
 1 file changed, 29 insertions(+), 20 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 915eb4a7c6..5df528ea81 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -15,22 +15,27 @@
 # - Tracked file replaced by submodule (replace_sub1_with_file =>
 #   replace_file_with_sub1)
 #
-#                   --O-----O
-#                  /  ^     replace_directory_with_sub1
-#                 /   replace_sub1_with_directory
-#                /----O
-#               /     ^
-#              /      modify_sub1
-#      O------O-------O
-#      ^      ^\      ^
-#      |      | \     remove_sub1
-#      |      |  -----O-----O
-#      |      |   \   ^     replace_file_with_sub1
-#      |      |    \  replace_sub1_with_file
-#      |   add_sub1 --O-----O
-# no_submodule        ^     valid_sub1
-#                     invalid_sub1
+#                     ----O
+#                    /    ^
+#                   /     remove_sub1
+#                  /
+#       add_sub1  /-------O
+#             |  /        ^
+#             | /         modify_sub1
+#             v/
+#      O------O-----------O---------O
+#      ^       \          ^         replace_directory_with_sub1
+#      |        \         replace_sub1_with_directory
+# no_submodule   \
+#                 --------O---------O
+#                  \      ^         replace_file_with_sub1
+#                   \     replace_sub1_with_file
+#                    \
+#                     ----O---------O
+#                         ^         valid_sub1
+#                         invalid_sub1
 #
+
 create_lib_submodule_repo () {
 	git init submodule_update_repo &&
 	(
@@ -49,10 +54,11 @@ create_lib_submodule_repo () {
 		git config submodule.sub1.ignore all &&
 		git add .gitmodules &&
 		git commit -m "Add sub1" &&
-		git checkout -b remove_sub1 &&
+
+		git checkout -b remove_sub1 add_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "modify_sub1" "add_sub1" &&
+		git checkout -b modify_sub1 add_sub1 &&
 		git submodule update &&
 		(
 			cd sub1 &&
@@ -67,7 +73,7 @@ create_lib_submodule_repo () {
 		git add sub1 &&
 		git commit -m "Modify sub1" &&
 
-		git checkout -b "replace_sub1_with_directory" "add_sub1" &&
+		git checkout -b replace_sub1_with_directory add_sub1 &&
 		git submodule update &&
 		git -C sub1 checkout modifications &&
 		git rm --cached sub1 &&
@@ -75,22 +81,25 @@ create_lib_submodule_repo () {
 		git config -f .gitmodules --remove-section "submodule.sub1" &&
 		git add .gitmodules sub1/* &&
 		git commit -m "Replace sub1 with directory" &&
+
 		git checkout -b replace_directory_with_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "replace_sub1_with_file" "add_sub1" &&
+		git checkout -b replace_sub1_with_file add_sub1 &&
 		git rm sub1 &&
 		echo "content" >sub1 &&
 		git add sub1 &&
 		git commit -m "Replace sub1 with file" &&
+
 		git checkout -b replace_file_with_sub1 &&
 		git revert HEAD &&
 
-		git checkout -b "invalid_sub1" "add_sub1" &&
+		git checkout -b invalid_sub1 add_sub1 &&
 		git update-index --cacheinfo 160000 0123456789012345678901234567890123456789 sub1 &&
 		git commit -m "Invalid sub1 commit" &&
 		git checkout -b valid_sub1 &&
 		git revert HEAD &&
+
 		git checkout master
 	)
 }
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 04/19] lib-submodule-update.sh: do not use ./. as submodule remote

[Stefan Beller]

Adding the repository itself as a submodule does not make sense in the
real world. In our test suite we used to do that out of convenience in
some tests as the current repository has easiest access for setting up
'just a submodule'.

However this doesn't quite test the real world, so let's do not follow
this pattern any further and actually create an independent repository
that we can use as a submodule.

When using './.' as the remote the superproject and submodule share the
same objects, such that testing if a given sha1 is a valid commit works
in either repository.  As running commands in an unpopulated submodule
fall back to the superproject, this happens in `reset_work_tree_to`
to determine if we need to populate the submodule. Fix this bug by
checking in the actual remote now.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 5df528ea81..c0d6325133 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -37,6 +37,17 @@
 #
 
 create_lib_submodule_repo () {
+	git init submodule_update_sub1 &&
+	(
+		cd submodule_update_sub1 &&
+		echo "expect" >>.gitignore &&
+		echo "actual" >>.gitignore &&
+		echo "x" >file1 &&
+		echo "y" >file2 &&
+		git add .gitignore file1 file2 &&
+		git commit -m "Base inside first submodule" &&
+		git branch "no_submodule"
+	) &&
 	git init submodule_update_repo &&
 	(
 		cd submodule_update_repo &&
@@ -49,7 +60,7 @@ create_lib_submodule_repo () {
 		git branch "no_submodule" &&
 
 		git checkout -b "add_sub1" &&
-		git submodule add ./. sub1 &&
+		git submodule add ../submodule_update_sub1 sub1 &&
 		git config -f .gitmodules submodule.sub1.ignore all &&
 		git config submodule.sub1.ignore all &&
 		git add .gitmodules &&
@@ -162,7 +173,7 @@ reset_work_tree_to () {
 		test_must_be_empty actual &&
 		sha1=$(git rev-parse --revs-only HEAD:sub1) &&
 		if test -n "$sha1" &&
-		   test $(cd "sub1" && git rev-parse --verify "$sha1^{commit}")
+		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$sha1^{commit}")
 		then
 			git submodule update --init --recursive "sub1"
 		fi
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 05/19] lib-submodule-update: teach test_submodule_content the -C <dir> flag

[Stefan Beller]

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index c0d6325133..00128f28b5 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -193,6 +193,11 @@ test_superproject_content () {
 # Test that the given submodule at path "$1" contains the content according
 # to the submodule commit recorded in the superproject's commit "$2"
 test_submodule_content () {
+	if test x"$1" = "x-C"
+	then
+		cd "$2"
+		shift; shift;
+	fi
 	if test $# != 2
 	then
 		echo "test_submodule_content needs two arguments"
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 06/19] lib-submodule-update.sh: replace sha1 by hash

[Stefan Beller]

Cleaning up code by generalising it.
Currently the mailing list discusses yet again how
to migrate away from sha1.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 00128f28b5..f52c49c838 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -171,9 +171,9 @@ reset_work_tree_to () {
 		git checkout -f "$1" &&
 		git status -u -s >actual &&
 		test_must_be_empty actual &&
-		sha1=$(git rev-parse --revs-only HEAD:sub1) &&
-		if test -n "$sha1" &&
-		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$sha1^{commit}")
+		hash=$(git rev-parse --revs-only HEAD:sub1) &&
+		if test -n "$hash" &&
+		   test $(cd "../submodule_update_sub1" && git rev-parse --verify "$hash^{commit}")
 		then
 			git submodule update --init --recursive "sub1"
 		fi
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 07/19] lib-submodule-update.sh: define tests for recursing into submodules

[Stefan Beller]

Currently lib-submodule-update.sh provides 2 functions
test_submodule_switch and test_submodule_forced_switch that are used by a
variety of tests to ensure that submodules behave as expected. The current
expected behavior is that submodules are not touched at all (see
42639d2317a for the exact setup).

In the future we want to teach all these commands to recurse
into submodules. To do that, we'll add two testing functions to
submodule-update-lib.sh: test_submodule_switch_recursing and
test_submodule_forced_switch_recursing.

These two functions behave in analogy to the already existing functions
just with a different expectation on submodule behavior. The submodule
in the working tree is expected to be updated to the recorded submodule
version. The behavior is analogous to e.g. the behavior of files in a
nested directory in the working tree, where a change to the working tree
handles any arising directory/file conflicts just fine.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/lib-submodule-update.sh | 506 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 504 insertions(+), 2 deletions(-)

diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index f52c49c838..ae560dc95c 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -4,6 +4,7 @@
 # - New submodule (no_submodule => add_sub1)
 # - Removed submodule (add_sub1 => remove_sub1)
 # - Updated submodule (add_sub1 => modify_sub1)
+# - Updated submodule recursively (add_nested_sub => modify_sub1_recursively)
 # - Submodule updated to invalid commit (add_sub1 => invalid_sub1)
 # - Submodule updated from invalid commit (invalid_sub1 => valid_sub1)
 # - Submodule replaced by tracked files in directory (add_sub1 =>
@@ -19,8 +20,8 @@
 #                    /    ^
 #                   /     remove_sub1
 #                  /
-#       add_sub1  /-------O
-#             |  /        ^
+#       add_sub1  /-------O---------O--------O  modify_sub1_recursively
+#             |  /        ^         add_nested_sub
 #             | /         modify_sub1
 #             v/
 #      O------O-----------O---------O
@@ -48,6 +49,17 @@ create_lib_submodule_repo () {
 		git commit -m "Base inside first submodule" &&
 		git branch "no_submodule"
 	) &&
+	git init submodule_update_sub2 &&
+	(
+		cd submodule_update_sub2
+		echo "expect" >>.gitignore &&
+		echo "actual" >>.gitignore &&
+		echo "x" >file1 &&
+		echo "y" >file2 &&
+		git add .gitignore file1 file2 &&
+		git commit -m "nested submodule base" &&
+		git branch "no_submodule"
+	) &&
 	git init submodule_update_repo &&
 	(
 		cd submodule_update_repo &&
@@ -84,6 +96,26 @@ create_lib_submodule_repo () {
 		git add sub1 &&
 		git commit -m "Modify sub1" &&
 
+		git checkout -b add_nested_sub modify_sub1 &&
+		git -C sub1 checkout -b "add_nested_sub" &&
+		git -C sub1 submodule add --branch no_submodule ../submodule_update_sub2 sub2 &&
+		git -C sub1 commit -a -m "add a nested submodule" &&
+		git add sub1 &&
+		git commit -a -m "update submodule, that updates a nested submodule" &&
+		git checkout -b modify_sub1_recursively &&
+		git -C sub1 checkout -b modify_sub1_recursively &&
+		git -C sub1/sub2 checkout -b modify_sub1_recursively &&
+		echo change >sub1/sub2/file3 &&
+		git -C sub1/sub2 add file3 &&
+		git -C sub1/sub2 commit -m "make a change in nested sub" &&
+		git -C sub1 add sub2 &&
+		git -C sub1 commit -m "update nested sub" &&
+		git add sub1 &&
+		git commit -m "update sub1, that updates nested sub" &&
+		git -C sub1 push origin modify_sub1_recursively &&
+		git -C sub1/sub2 push origin modify_sub1_recursively &&
+		git -C sub1 submodule deinit -f --all &&
+
 		git checkout -b replace_sub1_with_directory add_sub1 &&
 		git submodule update &&
 		git -C sub1 checkout modifications &&
@@ -150,6 +182,15 @@ test_git_directory_is_unchanged () {
 	)
 }
 
+test_git_directory_exists() {
+	test -e ".git/modules/$1" &&
+	if test -f sub1/.git
+	then
+		# does core.worktree point at the right place?
+		test "$(git -C .git/modules/$1 config core.worktree)" = "../../../$1"
+	fi
+}
+
 # Helper function to be executed at the start of every test below, it sets up
 # the submodule repo if it doesn't exist and configures the most problematic
 # settings for diff.ignoreSubmodules.
@@ -180,6 +221,27 @@ reset_work_tree_to () {
 	)
 }
 
+reset_work_tree_to_interested () {
+	reset_work_tree_to $1 &&
+	# make the submodule git dirs available
+	if ! test -d submodule_update/.git/modules/sub1
+	then
+		mkdir -p submodule_update/.git/modules &&
+		cp -r submodule_update_repo/.git/modules/sub1 submodule_update/.git/modules/sub1
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1 config --unset core.worktree
+	fi &&
+	if ! test -d submodule_update/.git/modules/sub1/modules/sub2
+	then
+		mkdir -p submodule_update/.git/modules/sub1/modules &&
+		cp -r submodule_update_repo/.git/modules/sub1/modules/sub2 submodule_update/.git/modules/sub1/modules/sub2
+		GIT_WORK_TREE=. git -C submodule_update/.git/modules/sub1/modules/sub2 config --unset core.worktree
+	fi &&
+	# indicate we are interested in the submodule:
+	git -C submodule_update config submodule.sub1.url "bogus" &&
+	# sub1 might not be checked out, so use the git dir
+	git -C submodule_update/.git/modules/sub1 config submodule.sub2.url "bogus"
+}
+
 # Test that the superproject contains the content according to commit "$1"
 # (the work tree must match the index for everything but submodules but the
 # index must exactly match the given commit including any submodule SHA-1s).
@@ -700,3 +762,443 @@ test_submodule_forced_switch () {
 		)
 	'
 }
+
+# Test that submodule contents are correctly updated when switching
+# between commits that change a submodule.
+# Test that the following transitions are correctly handled:
+# (These tests are also above in the case where we expect no change
+#  in the submodule)
+# - Updated submodule
+# - New submodule
+# - Removed submodule
+# - Directory containing tracked files replaced by submodule
+# - Submodule replaced by tracked files in directory
+# - Submodule replaced by tracked file with the same name
+# - tracked file replaced by submodule
+#
+# New test cases
+# - Removing a submodule with a git directory absorbs the submodules
+#   git directory first into the superproject.
+
+test_submodule_switch_recursing () {
+	command="$1"
+	######################### Appearing submodule #########################
+	# Switching to a commit letting a submodule appear checks it out ...
+	test_expect_success "$command: added submodule is checked out" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... ignoring an empty existing directory ...
+	test_expect_success "$command: added submodule is checked out in empty dir" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			mkdir sub1 &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... unless there is an untracked file in its place.
+	test_expect_success "$command: added submodule doesn't remove untracked file with same name" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			: >sub1 &&
+			test_must_fail $command add_sub1 &&
+			test_superproject_content origin/no_submodule &&
+			test_must_be_empty sub1
+		)
+	'
+	# ... but an ignored file is fine.
+	test_expect_success "$command: added submodule removes an untracked ignored file" '
+		test_when_finished "rm submodule_update/.git/info/exclude" &&
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			: >sub1 &&
+			echo sub1 >.git/info/exclude
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Replacing a tracked file with a submodule produces a checked out submodule
+	test_expect_success "$command: replace tracked file with submodule checks out submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_file &&
+		(
+			cd submodule_update &&
+			git branch -t replace_file_with_sub1 origin/replace_file_with_sub1 &&
+			$command replace_file_with_sub1 &&
+			test_superproject_content origin/replace_file_with_sub1 &&
+			test_submodule_content sub1 origin/replace_file_with_sub1
+		)
+	'
+	# ... as does removing a directory with tracked files with a submodule.
+	test_expect_success "$command: replace directory with submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_directory &&
+		(
+			cd submodule_update &&
+			git branch -t replace_directory_with_sub1 origin/replace_directory_with_sub1 &&
+			$command replace_directory_with_sub1 &&
+			test_superproject_content origin/replace_directory_with_sub1 &&
+			test_submodule_content sub1 origin/replace_directory_with_sub1
+		)
+	'
+
+	######################## Disappearing submodule #######################
+	# Removing a submodule removes its work tree ...
+	test_expect_success "$command: removed submodule removes submodules working tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1
+		)
+	'
+	# ... absorbing a .git directory along the way.
+	test_expect_success "$command: removed submodule absorbs submodules .git directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1 &&
+			test_git_directory_exists sub1
+		)
+	'
+	# Replacing a submodule with files in a directory must succeeds
+	# when the submodule is clean
+	test_expect_success "$command: replace submodule with a directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_submodule_content sub1 origin/replace_sub1_with_directory
+		)
+	'
+	# ... absorbing a .git directory.
+	test_expect_success "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_git_directory_exists sub1
+		)
+	'
+
+	# Replacing it with a file ...
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file &&
+			test -f sub1
+		)
+	'
+
+	# ... must check its local work tree for untracked files
+	test_expect_success "$command: replace submodule with a file must fail with untracked files" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/untrackedfile &&
+			test_must_fail $command replace_sub1_with_file &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+
+	# ... and ignored files are ignored
+	test_expect_success "$command: replace submodule with a file works ignores ignored files in submodule" '
+		test_when_finished "rm submodule_update/.git/modules/sub1/info/exclude" &&
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/ignored &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file &&
+			test -f sub1
+		)
+	'
+
+	########################## Modified submodule #########################
+	# Updating a submodule sha1 updates the submodule's work tree
+	test_expect_success "$command: modified submodule updates submodule work tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1 origin/modify_sub1 &&
+			$command modify_sub1 &&
+			test_superproject_content origin/modify_sub1 &&
+			test_submodule_content sub1 origin/modify_sub1
+		)
+	'
+
+	# Updating a submodule to an invalid sha1 doesn't update the
+	# superproject nor the submodule's work tree.
+	test_expect_success "$command: updating to a missing submodule commit fails" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t invalid_sub1 origin/invalid_sub1 &&
+			test_must_fail $command invalid_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+
+	test_expect_success "$command: modified submodule updates submodule recursively" '
+		prolog &&
+		reset_work_tree_to_interested add_nested_sub &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1_recursively origin/modify_sub1_recursively &&
+			$command modify_sub1_recursively &&
+			test_superproject_content origin/modify_sub1_recursively &&
+			test_submodule_content sub1 origin/modify_sub1_recursively &&
+			test_submodule_content -C sub1 sub2 origin/modify_sub1_recursively
+		)
+	'
+}
+
+# Test that submodule contents are updated when switching between commits
+# that change a submodule, but throwing away local changes in
+# the superproject as well as the submodule is allowed.
+test_submodule_forced_switch_recursing () {
+	command="$1"
+	######################### Appearing submodule #########################
+	# Switching to a commit letting a submodule appear creates empty dir ...
+	test_expect_success "$command: added submodule is checked out" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... and doesn't care if it already exists ...
+	test_expect_success "$command: added submodule ignores empty directory" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			mkdir sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# ... not caring about an untracked file either
+	test_expect_success "$command: added submodule does remove untracked unignored file with same name when forced" '
+		prolog &&
+		reset_work_tree_to_interested no_submodule &&
+		(
+			cd submodule_update &&
+			git branch -t add_sub1 origin/add_sub1 &&
+			>sub1 &&
+			$command add_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Replacing a tracked file with a submodule checks out the submodule
+	test_expect_success "$command: replace tracked file with submodule populates the submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_file &&
+		(
+			cd submodule_update &&
+			git branch -t replace_file_with_sub1 origin/replace_file_with_sub1 &&
+			$command replace_file_with_sub1 &&
+			test_superproject_content origin/replace_file_with_sub1 &&
+			test_submodule_content sub1 origin/replace_file_with_sub1
+		)
+	'
+	# ... as does removing a directory with tracked files with a
+	# submodule.
+	test_expect_success "$command: replace directory with submodule" '
+		prolog &&
+		reset_work_tree_to_interested replace_sub1_with_directory &&
+		(
+			cd submodule_update &&
+			git branch -t replace_directory_with_sub1 origin/replace_directory_with_sub1 &&
+			$command replace_directory_with_sub1 &&
+			test_superproject_content origin/replace_directory_with_sub1 &&
+			test_submodule_content sub1 origin/replace_directory_with_sub1
+		)
+	'
+
+	######################## Disappearing submodule #######################
+	# Removing a submodule doesn't remove its work tree ...
+	test_expect_success "$command: removed submodule leaves submodule directory and its contents in place" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			! test -e sub1
+		)
+	'
+	# ... especially when it contains a .git directory.
+	test_expect_success "$command: removed submodule leaves submodule containing a .git directory alone" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t remove_sub1 origin/remove_sub1 &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules/sub1 &&
+			$command remove_sub1 &&
+			test_superproject_content origin/remove_sub1 &&
+			test_git_directory_exists sub1 &&
+			! test -e sub1
+		)
+	'
+	# Replacing a submodule with files in a directory ...
+	test_expect_success "$command: replace submodule with a directory" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory
+		)
+	'
+	# ... absorbing a .git directory.
+	test_expect_success "$command: replace submodule containing a .git directory with a directory must fail" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_directory origin/replace_sub1_with_directory &&
+			replace_gitfile_with_git_dir sub1 &&
+			rm -rf .git/modules/sub1 &&
+			$command replace_sub1_with_directory &&
+			test_superproject_content origin/replace_sub1_with_directory &&
+			test_submodule_content sub1 origin/modify_sub1
+			test_git_directory_exists sub1
+		)
+	'
+	# Replacing it with a file
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file
+		)
+	'
+
+	# ... even if the submodule contains ignored files
+	test_expect_success "$command: replace submodule with a file ignoring ignored files" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/expect &&
+			$command replace_sub1_with_file &&
+			test_superproject_content origin/replace_sub1_with_file
+		)
+	'
+
+	# ... but stops for untracked files that would be lost
+	test_expect_success "$command: replace submodule with a file" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t replace_sub1_with_file origin/replace_sub1_with_file &&
+			: >sub1/untracked_file &&
+			test_must_fail $command replace_sub1_with_file &&
+			test_superproject_content origin/add_sub1 &&
+			test -f sub1/untracked_file
+		)
+	'
+
+	########################## Modified submodule #########################
+	# Updating a submodule sha1 updates the submodule's work tree
+	test_expect_success "$command: modified submodule updates submodule work tree" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t modify_sub1 origin/modify_sub1 &&
+			$command modify_sub1 &&
+			test_superproject_content origin/modify_sub1 &&
+			test_submodule_content sub1 origin/modify_sub1
+		)
+	'
+	# Updating a submodule to an invalid sha1 doesn't update the
+	# submodule's work tree, subsequent update will fail
+	test_expect_success "$command: modified submodule does not update submodule work tree to invalid commit" '
+		prolog &&
+		reset_work_tree_to_interested add_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t invalid_sub1 origin/invalid_sub1 &&
+			test_must_fail $command invalid_sub1 &&
+			test_superproject_content origin/add_sub1 &&
+			test_submodule_content sub1 origin/add_sub1
+		)
+	'
+	# Updating a submodule from an invalid sha1 updates
+	test_expect_success "$command: modified submodule does not update submodule work tree from invalid commit" '
+		prolog &&
+		reset_work_tree_to_interested invalid_sub1 &&
+		(
+			cd submodule_update &&
+			git branch -t valid_sub1 origin/valid_sub1 &&
+			test_must_fail $command valid_sub1 &&
+			test_superproject_content origin/invalid_sub1
+		)
+	'
+}
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 08/19] make is_submodule_populated gently

[Stefan Beller]

We need the gentle version in a later patch. As we have just one caller,
migrate the caller.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/grep.c | 2 +-
 submodule.c    | 7 ++-----
 submodule.h    | 8 +++++++-
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/builtin/grep.c b/builtin/grep.c
index 2c727ef499..b17835aed6 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -616,7 +616,7 @@ static int grep_submodule(struct grep_opt *opt, const unsigned char *sha1,
 {
 	if (!is_submodule_initialized(path))
 		return 0;
-	if (!is_submodule_populated(path)) {
+	if (!is_submodule_populated_gently(path, NULL)) {
 		/*
 		 * If searching history, check for the presense of the
 		 * submodule's gitdir before skipping the submodule.
diff --git a/submodule.c b/submodule.c
index 45e93a1d55..04d185738f 100644
--- a/submodule.c
+++ b/submodule.c
@@ -234,15 +234,12 @@ int is_submodule_initialized(const char *path)
 	return ret;
 }
 
-/*
- * Determine if a submodule has been populated at a given 'path'
- */
-int is_submodule_populated(const char *path)
+int is_submodule_populated_gently(const char *path, int *return_error_code)
 {
 	int ret = 0;
 	char *gitdir = xstrfmt("%s/.git", path);
 
-	if (resolve_gitdir(gitdir))
+	if (resolve_gitdir_gently(gitdir, return_error_code))
 		ret = 1;
 
 	free(gitdir);
diff --git a/submodule.h b/submodule.h
index 05ab674f06..0b915bd3ac 100644
--- a/submodule.h
+++ b/submodule.h
@@ -41,7 +41,13 @@ extern int submodule_config(const char *var, const char *value, void *cb);
 extern void gitmodules_config(void);
 extern void gitmodules_config_sha1(const unsigned char *commit_sha1);
 extern int is_submodule_initialized(const char *path);
-extern int is_submodule_populated(const char *path);
+/*
+ * Determine if a submodule has been populated at a given 'path' by checking if
+ * the <path>/.git resolves to a valid git repository.
+ * If return_error_code is NULL, die on error.
+ * Otherwise the return error code is the same as of resolve_gitdir_gently.
+ */
+extern int is_submodule_populated_gently(const char *path, int *return_error_code);
 extern int parse_submodule_update_strategy(const char *value,
 		struct submodule_update_strategy *dst);
 extern const char *submodule_strategy_to_string(const struct submodule_update_strategy *s);
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 09/19] update submodules: add submodule config parsing

[Stefan Beller]

Similar to b33a15b08 (push: add recurseSubmodules config option,
2015-11-17) and 027771fcb1 (submodule: allow erroneous values for the
fetchRecurseSubmodules option, 2015-08-17), we add submodule-config code
that is later used to parse whether we are interested in updating
submodules.

We need the `die_on_error` parameter to be able to call this parsing
function for the config file as well, which if incorrect lets Git die.

As we're just touching the header file, also mark all functions extern.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule-config.c | 20 ++++++++++++++++++++
 submodule-config.h | 17 +++++++++--------
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/submodule-config.c b/submodule-config.c
index 93453909cf..3e8e380d98 100644
--- a/submodule-config.c
+++ b/submodule-config.c
@@ -234,6 +234,26 @@ int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg)
 	return parse_fetch_recurse(opt, arg, 1);
 }
 
+static int parse_update_recurse(const char *opt, const char *arg,
+				int die_on_error)
+{
+	switch (git_config_maybe_bool(opt, arg)) {
+	case 1:
+		return RECURSE_SUBMODULES_ON;
+	case 0:
+		return RECURSE_SUBMODULES_OFF;
+	default:
+		if (die_on_error)
+			die("bad %s argument: %s", opt, arg);
+		return RECURSE_SUBMODULES_ERROR;
+	}
+}
+
+int parse_update_recurse_submodules_arg(const char *opt, const char *arg)
+{
+	return parse_update_recurse(opt, arg, 1);
+}
+
 static int parse_push_recurse(const char *opt, const char *arg,
 			       int die_on_error)
 {
diff --git a/submodule-config.h b/submodule-config.h
index 70f19363fd..d434ecdb45 100644
--- a/submodule-config.h
+++ b/submodule-config.h
@@ -22,16 +22,17 @@ struct submodule {
 	int recommend_shallow;
 };
 
-int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg);
-int parse_push_recurse_submodules_arg(const char *opt, const char *arg);
-int parse_submodule_config_option(const char *var, const char *value);
-const struct submodule *submodule_from_name(const unsigned char *commit_or_tree,
-		const char *name);
-const struct submodule *submodule_from_path(const unsigned char *commit_or_tree,
-		const char *path);
+extern int parse_fetch_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_update_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_push_recurse_submodules_arg(const char *opt, const char *arg);
+extern int parse_submodule_config_option(const char *var, const char *value);
+extern const struct submodule *submodule_from_name(
+		const unsigned char *commit_or_tree, const char *name);
+extern const struct submodule *submodule_from_path(
+		const unsigned char *commit_or_tree, const char *path);
 extern int gitmodule_sha1_from_commit(const unsigned char *commit_sha1,
 				      unsigned char *gitmodules_sha1,
 				      struct strbuf *rev);
-void submodule_free(void);
+extern void submodule_free(void);
 
 #endif /* SUBMODULE_CONFIG_H */
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 10/19] update submodules: add a config option to determine if submodules are updated

[Stefan Beller]

In later patches we introduce the options and flag for commands
that modify the working directory, e.g. git-checkout.

Have a central place to store such settings whether we want to update
a submodule.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 6 ++++++
 submodule.h | 1 +
 2 files changed, 7 insertions(+)

diff --git a/submodule.c b/submodule.c
index 04d185738f..591f4a694e 100644
--- a/submodule.c
+++ b/submodule.c
@@ -17,6 +17,7 @@
 #include "worktree.h"
 
 static int config_fetch_recurse_submodules = RECURSE_SUBMODULES_ON_DEMAND;
+static int config_update_recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 static int parallel_jobs = 1;
 static struct string_list changed_submodule_paths = STRING_LIST_INIT_NODUP;
 static int initialized_fetch_ref_tips;
@@ -542,6 +543,11 @@ void set_config_fetch_recurse_submodules(int value)
 	config_fetch_recurse_submodules = value;
 }
 
+void set_config_update_recurse_submodules(int value)
+{
+	config_update_recurse_submodules = value;
+}
+
 static int has_remote(const char *refname, const struct object_id *oid,
 		      int flags, void *cb_data)
 {
diff --git a/submodule.h b/submodule.h
index 0b915bd3ac..b4e60c08d2 100644
--- a/submodule.h
+++ b/submodule.h
@@ -64,6 +64,7 @@ extern void show_submodule_inline_diff(FILE *f, const char *path,
 		const char *del, const char *add, const char *reset,
 		const struct diff_options *opt);
 extern void set_config_fetch_recurse_submodules(int value);
+extern void set_config_update_recurse_submodules(int value);
 extern void check_for_new_submodule_commits(unsigned char new_sha1[20]);
 extern int fetch_populated_submodules(const struct argv_array *options,
 			       const char *prefix, int command_line_option,
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 11/19] submodules: introduce check to see whether to touch a submodule

[Stefan Beller]

In later patches we introduce the --recurse-submodule flag for commands
that modify the working directory, e.g. git-checkout.

It is potentially expensive to check if a submodule needs an update,
because a common theme to interact with submodules is to spawn a child
process for each interaction.

So let's introduce a function that checks if a submodule needs
to be checked for an update before attempting the update.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 16 ++++++++++++++++
 submodule.h |  7 +++++++
 2 files changed, 23 insertions(+)

diff --git a/submodule.c b/submodule.c
index 591f4a694e..8b2c0212be 100644
--- a/submodule.c
+++ b/submodule.c
@@ -548,6 +548,22 @@ void set_config_update_recurse_submodules(int value)
 	config_update_recurse_submodules = value;
 }
 
+int should_update_submodules(void)
+{
+	return config_update_recurse_submodules == RECURSE_SUBMODULES_ON;
+}
+
+const struct submodule *submodule_from_ce(const struct cache_entry *ce)
+{
+	if (!S_ISGITLINK(ce->ce_mode))
+		return NULL;
+
+	if (!should_update_submodules())
+		return NULL;
+
+	return submodule_from_path(null_sha1, ce->name);
+}
+
 static int has_remote(const char *refname, const struct object_id *oid,
 		      int flags, void *cb_data)
 {
diff --git a/submodule.h b/submodule.h
index b4e60c08d2..6f3fe85c7c 100644
--- a/submodule.h
+++ b/submodule.h
@@ -65,6 +65,13 @@ extern void show_submodule_inline_diff(FILE *f, const char *path,
 		const struct diff_options *opt);
 extern void set_config_fetch_recurse_submodules(int value);
 extern void set_config_update_recurse_submodules(int value);
+/* Check if we want to update any submodule.*/
+extern int should_update_submodules(void);
+/*
+ * Returns the submodule struct if the given ce entry is a submodule
+ * and it should be updated. Returns NULL otherwise.
+ */
+extern const struct submodule *submodule_from_ce(const struct cache_entry *ce);
 extern void check_for_new_submodule_commits(unsigned char new_sha1[20]);
 extern int fetch_populated_submodules(const struct argv_array *options,
 			       const char *prefix, int command_line_option,
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 12/19] update submodules: move up prepare_submodule_repo_env

[Stefan Beller]

In a later patch we need to prepare the submodule environment with
another git directory, so split up the function.

Also move it up in the file such that we do not need to declare the
function later before using it.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/submodule.c b/submodule.c
index 8b2c0212be..0b2596e88a 100644
--- a/submodule.c
+++ b/submodule.c
@@ -356,6 +356,23 @@ static void print_submodule_summary(struct rev_info *rev, FILE *f,
 	strbuf_release(&sb);
 }
 
+static void prepare_submodule_repo_env_no_git_dir(struct argv_array *out)
+{
+	const char * const *var;
+
+	for (var = local_repo_env; *var; var++) {
+		if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
+			argv_array_push(out, *var);
+	}
+}
+
+void prepare_submodule_repo_env(struct argv_array *out)
+{
+	prepare_submodule_repo_env_no_git_dir(out);
+	argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
+			 DEFAULT_GIT_DIR_ENVIRONMENT);
+}
+
 /* Helper function to display the submodule header line prior to the full
  * summary output. If it can locate the submodule objects directory it will
  * attempt to lookup both the left and right commits and put them into the
@@ -1390,18 +1407,6 @@ int parallel_submodules(void)
 	return parallel_jobs;
 }
 
-void prepare_submodule_repo_env(struct argv_array *out)
-{
-	const char * const *var;
-
-	for (var = local_repo_env; *var; var++) {
-		if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
-			argv_array_push(out, *var);
-	}
-	argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
-			 DEFAULT_GIT_DIR_ENVIRONMENT);
-}
-
 /*
  * Embeds a single submodules git directory into the superprojects git dir,
  * non recursively.
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 13/19] submodule.c: get_super_prefix_or_empty

[Stefan Beller]

In a later patch we need to use the super_prefix, and
in case it is NULL we can just assume it is empty.
Create a helper function for this.

We already have some use cases for this helper function,
convert them, too.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/submodule.c b/submodule.c
index 0b2596e88a..3501497a78 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1239,6 +1239,14 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
 	return ret;
 }
 
+static const char *get_super_prefix_or_empty()
+{
+	const char *s = get_super_prefix();
+	if (!s)
+		s = "";
+	return s;
+}
+
 static int find_first_merges(struct object_array *result, const char *path,
 		struct commit *a, struct commit *b)
 {
@@ -1438,11 +1446,8 @@ static void relocate_single_git_dir_into_superproject(const char *prefix,
 		die(_("could not create directory '%s'"), new_git_dir);
 	real_new_git_dir = real_pathdup(new_git_dir);
 
-	if (!prefix)
-		prefix = get_super_prefix();
-
 	fprintf(stderr, _("Migrating git directory of '%s%s' from\n'%s' to\n'%s'\n"),
-		prefix ? prefix : "", path,
+		get_super_prefix_or_empty(), path,
 		real_old_git_dir, real_new_git_dir);
 
 	relocate_gitdir(path, real_old_git_dir, real_new_git_dir);
@@ -1513,8 +1518,7 @@ void absorb_git_dir_into_superproject(const char *prefix,
 		if (flags & ~ABSORB_GITDIR_RECURSE_SUBMODULES)
 			die("BUG: we don't know how to pass the flags down?");
 
-		if (get_super_prefix())
-			strbuf_addstr(&sb, get_super_prefix());
+		strbuf_addstr(&sb, get_super_prefix_or_empty());
 		strbuf_addstr(&sb, path);
 		strbuf_addch(&sb, '/');
 
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 14/19] update submodules: add submodule_move_head

[Stefan Beller]

In later patches we introduce the options and flag for commands
that modify the working directory, e.g. git-checkout.

This piece of code will be used universally for
all these working tree modifications as it
* supports dry run to answer the question:
  "Is it safe to change the submodule to this new state?"
  e.g. is it overwriting untracked files or are there local
  changes that would be overwritten?
* supports a force flag that can be used for resetting
  the tree.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 submodule.c | 137 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 submodule.h |   7 ++++
 2 files changed, 144 insertions(+)

diff --git a/submodule.c b/submodule.c
index 3501497a78..929fc7bf04 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1247,6 +1247,143 @@ static const char *get_super_prefix_or_empty()
 	return s;
 }
 
+static int submodule_has_dirty_index(const struct submodule *sub)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	argv_array_pushl(&cp.args, "diff-index", "--quiet",
+				   "--cached", "HEAD", NULL);
+	cp.no_stdin = 1;
+	cp.no_stdout = 1;
+	cp.dir = sub->path;
+	if (start_command(&cp))
+		die("could not recurse into submodule '%s'", sub->path);
+
+	return finish_command(&cp);
+}
+
+static void submodule_reset_index(const char *path)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.dir = path;
+
+	argv_array_pushf(&cp.args, "--super-prefix=%s%s/",
+				   get_super_prefix_or_empty(), path);
+	argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
+
+	argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);
+
+	if (run_command(&cp))
+		die("could not reset submodule index");
+}
+
+/**
+ * Moves a submodule at a given path from a given head to another new head.
+ * For edge cases (a submodule coming into existence or removing a submodule)
+ * pass NULL for old or new respectively.
+ */
+int submodule_move_head(const char *path,
+			 const char *old,
+			 const char *new,
+			 unsigned flags)
+{
+	int ret = 0;
+	struct child_process cp = CHILD_PROCESS_INIT;
+	const struct submodule *sub;
+
+	sub = submodule_from_path(null_sha1, path);
+
+	if (!sub)
+		die("BUG: could not get submodule information for '%s'", path);
+
+	if (old && !(flags & SUBMODULE_MOVE_HEAD_FORCE)) {
+		/* Check if the submodule has a dirty index. */
+		if (submodule_has_dirty_index(sub))
+			return error(_("submodule '%s' has dirty index"), path);
+	}
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
+		if (old) {
+			if (!submodule_uses_gitfile(path))
+				absorb_git_dir_into_superproject("", path,
+					ABSORB_GITDIR_RECURSE_SUBMODULES);
+		} else {
+			struct strbuf sb = STRBUF_INIT;
+			strbuf_addf(&sb, "%s/modules/%s",
+				    get_git_common_dir(), sub->name);
+			connect_work_tree_and_git_dir(path, sb.buf);
+			strbuf_release(&sb);
+
+			/* make sure the index is clean as well */
+			submodule_reset_index(path);
+		}
+	}
+
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.dir = path;
+
+	argv_array_pushf(&cp.args, "--super-prefix=%s%s/",
+			get_super_prefix_or_empty(), path);
+	argv_array_pushl(&cp.args, "read-tree", NULL);
+
+	if (flags & SUBMODULE_MOVE_HEAD_DRY_RUN)
+		argv_array_push(&cp.args, "-n");
+	else
+		argv_array_push(&cp.args, "-u");
+
+	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
+		argv_array_push(&cp.args, "--reset");
+	else
+		argv_array_push(&cp.args, "-m");
+
+	argv_array_push(&cp.args, old ? old : EMPTY_TREE_SHA1_HEX);
+	argv_array_push(&cp.args, new ? new : EMPTY_TREE_SHA1_HEX);
+
+	if (run_command(&cp)) {
+		ret = -1;
+		goto out;
+	}
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
+		if (new) {
+			struct child_process cp1 = CHILD_PROCESS_INIT;
+			/* also set the HEAD accordingly */
+			cp1.git_cmd = 1;
+			cp1.no_stdin = 1;
+			cp1.dir = path;
+
+			argv_array_pushl(&cp1.args, "update-ref", "HEAD",
+					 new ? new : EMPTY_TREE_SHA1_HEX, NULL);
+
+			if (run_command(&cp1)) {
+				ret = -1;
+				goto out;
+			}
+		} else {
+			struct strbuf sb = STRBUF_INIT;
+
+			strbuf_addf(&sb, "%s/.git", path);
+			unlink_or_warn(sb.buf);
+			strbuf_release(&sb);
+
+			if (is_empty_dir(path))
+				rmdir_or_warn(path);
+		}
+	}
+out:
+	return ret;
+}
+
 static int find_first_merges(struct object_array *result, const char *path,
 		struct commit *a, struct commit *b)
 {
diff --git a/submodule.h b/submodule.h
index 6f3fe85c7c..4cdf6445f7 100644
--- a/submodule.h
+++ b/submodule.h
@@ -96,6 +96,13 @@ extern int push_unpushed_submodules(struct sha1_array *commits,
 extern void connect_work_tree_and_git_dir(const char *work_tree, const char *git_dir);
 extern int parallel_submodules(void);
 
+#define SUBMODULE_MOVE_HEAD_DRY_RUN (1<<0)
+#define SUBMODULE_MOVE_HEAD_FORCE   (1<<1)
+extern int submodule_move_head(const char *path,
+			       const char *old,
+			       const char *new,
+			       unsigned flags);
+
 /*
  * Prepare the "env_array" parameter of a "struct child_process" for executing
  * a submodule by clearing any repo-specific envirionment variables, but
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 15/19] unpack-trees: pass old oid to verify_clean_submodule

[Stefan Beller]

The check (which uses the old oid) is yet to be implemented, but this part
is just a refactor, so it can go separately first.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 unpack-trees.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 3a8ee19fe8..616a0ae4b2 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1407,7 +1407,8 @@ static void invalidate_ce_path(const struct cache_entry *ce,
  * Currently, git does not checkout subprojects during a superproject
  * checkout, so it is not going to overwrite anything.
  */
-static int verify_clean_submodule(const struct cache_entry *ce,
+static int verify_clean_submodule(const char *old_sha1,
+				  const struct cache_entry *ce,
 				  enum unpack_trees_error_types error_type,
 				  struct unpack_trees_options *o)
 {
@@ -1427,16 +1428,18 @@ static int verify_clean_subdirectory(const struct cache_entry *ce,
 	struct dir_struct d;
 	char *pathbuf;
 	int cnt = 0;
-	unsigned char sha1[20];
 
-	if (S_ISGITLINK(ce->ce_mode) &&
-	    resolve_gitlink_ref(ce->name, "HEAD", sha1) == 0) {
-		/* If we are not going to update the submodule, then
+	if (S_ISGITLINK(ce->ce_mode)) {
+		unsigned char sha1[20];
+		int sub_head = resolve_gitlink_ref(ce->name, "HEAD", sha1);
+		/*
+		 * If we are not going to update the submodule, then
 		 * we don't care.
 		 */
-		if (!hashcmp(sha1, ce->oid.hash))
+		if (!sub_head && !hashcmp(sha1, ce->oid.hash))
 			return 0;
-		return verify_clean_submodule(ce, error_type, o);
+		return verify_clean_submodule(sub_head ? NULL : sha1_to_hex(sha1),
+					      ce, error_type, o);
 	}
 
 	/*
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 16/19] unpack-trees: check if we can perform the operation for submodules

[Stefan Beller]

In a later patch we'll support submodule entries to be
in sync with the tree in working tree changing commands,
such as checkout or read-tree.

When a new submodule entry changes in the tree, we need to
check if there are conflicts (directory/file conflicts)
for the tree. Add this check for submodules to be
performed before the working tree is touched.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 unpack-trees.c | 131 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
 unpack-trees.h |   1 +
 2 files changed, 123 insertions(+), 9 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 616a0ae4b2..8333da2cc9 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -10,6 +10,8 @@
 #include "attr.h"
 #include "split-index.h"
 #include "dir.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 /*
  * Error messages expected by scripts out of plumbing commands such as
@@ -45,6 +47,9 @@ static const char *unpack_plumbing_errors[NB_UNPACK_TREES_ERROR_TYPES] = {
 
 	/* ERROR_WOULD_LOSE_ORPHANED_REMOVED */
 	"Working tree file '%s' would be removed by sparse checkout update.",
+
+	/* ERROR_WOULD_LOSE_SUBMODULE */
+	"Submodule '%s' cannot checkout new HEAD.",
 };
 
 #define ERRORMSG(o,type) \
@@ -161,6 +166,8 @@ void setup_unpack_trees_porcelain(struct unpack_trees_options *opts,
 		_("The following working tree files would be overwritten by sparse checkout update:\n%s");
 	msgs[ERROR_WOULD_LOSE_ORPHANED_REMOVED] =
 		_("The following working tree files would be removed by sparse checkout update:\n%s");
+	msgs[ERROR_WOULD_LOSE_SUBMODULE] =
+		_("Submodule '%s' cannot checkout new HEAD");
 
 	opts->show_all_errors = 1;
 	/* rejected paths may not have a static buffer */
@@ -240,12 +247,75 @@ static void display_error_msgs(struct unpack_trees_options *o)
 		fprintf(stderr, _("Aborting\n"));
 }
 
+static int check_submodule_move_head(const struct cache_entry *ce,
+				     const char *old_id,
+				     const char *new_id,
+				     struct unpack_trees_options *o)
+{
+	const struct submodule *sub = submodule_from_ce(ce);
+	if (!sub)
+		return 0;
+
+	switch (sub->update_strategy.type) {
+	case SM_UPDATE_UNSPECIFIED:
+	case SM_UPDATE_CHECKOUT:
+		if (submodule_move_head(ce->name, old_id, new_id, SUBMODULE_MOVE_HEAD_DRY_RUN))
+			return o->gently ? -1 :
+				add_rejected_path(o, ERROR_WOULD_LOSE_SUBMODULE, ce->name);
+		return 0;
+	case SM_UPDATE_NONE:
+		return 0;
+	case SM_UPDATE_REBASE:
+	case SM_UPDATE_MERGE:
+	case SM_UPDATE_COMMAND:
+	default:
+		warning(_("submodule update strategy not supported for submodule '%s'"), ce->name);
+		return -1;
+	}
+}
+
+static void reload_gitmodules_file(struct index_state *index,
+				   struct checkout *state)
+{
+	int i;
+	for (i = 0; i < index->cache_nr; i++) {
+		struct cache_entry *ce = index->cache[i];
+		if (ce->ce_flags & CE_UPDATE) {
+			int r = strcmp(ce->name, ".gitmodules");
+			if (r < 0)
+				continue;
+			else if (r == 0) {
+				submodule_free();
+				checkout_entry(ce, state, NULL);
+				gitmodules_config();
+				git_config(submodule_config, NULL);
+			} else
+				break;
+		}
+	}
+}
+
 /*
  * Unlink the last component and schedule the leading directories for
  * removal, such that empty directories get removed.
  */
 static void unlink_entry(const struct cache_entry *ce)
 {
+	const struct submodule *sub = submodule_from_ce(ce);
+	if (sub) {
+		switch (sub->update_strategy.type) {
+		case SM_UPDATE_UNSPECIFIED:
+		case SM_UPDATE_CHECKOUT:
+		case SM_UPDATE_REBASE:
+		case SM_UPDATE_MERGE:
+			submodule_move_head(ce->name, "HEAD", NULL,
+					    SUBMODULE_MOVE_HEAD_FORCE);
+			break;
+		case SM_UPDATE_NONE:
+		case SM_UPDATE_COMMAND:
+			return; /* Do not touch the submodule. */
+		}
+	}
 	if (!check_leading_path(ce->name, ce_namelen(ce)))
 		return;
 	if (remove_or_warn(ce->ce_mode, ce->name))
@@ -301,6 +371,9 @@ static int check_updates(struct unpack_trees_options *o)
 	remove_marked_cache_entries(index);
 	remove_scheduled_dirs();
 
+	if (should_update_submodules() && o->update && !o->dry_run)
+		reload_gitmodules_file(index, &state);
+
 	for (i = 0; i < index->cache_nr; i++) {
 		struct cache_entry *ce = index->cache[i];
 
@@ -1358,17 +1431,26 @@ static int verify_uptodate_1(const struct cache_entry *ce,
 	if (!lstat(ce->name, &st)) {
 		int flags = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE;
 		unsigned changed = ie_match_stat(o->src_index, ce, &st, flags);
+
+		if (submodule_from_ce(ce)) {
+			int r = check_submodule_move_head(ce,
+				"HEAD", oid_to_hex(&ce->oid), o);
+			if (r)
+				return o->gently ? -1 :
+					add_rejected_path(o, error_type, ce->name);
+			return 0;
+		}
+
 		if (!changed)
 			return 0;
 		/*
-		 * NEEDSWORK: the current default policy is to allow
-		 * submodule to be out of sync wrt the superproject
-		 * index.  This needs to be tightened later for
-		 * submodules that are marked to be automatically
-		 * checked out.
+		 * Historic default policy was to allow submodule to be out
+		 * of sync wrt the superproject index. If the submodule was
+		 * not considered interesting above, we don't care here.
 		 */
 		if (S_ISGITLINK(ce->ce_mode))
 			return 0;
+
 		errno = 0;
 	}
 	if (errno == ENOENT)
@@ -1412,7 +1494,11 @@ static int verify_clean_submodule(const char *old_sha1,
 				  enum unpack_trees_error_types error_type,
 				  struct unpack_trees_options *o)
 {
-	return 0;
+	if (!submodule_from_ce(ce))
+		return 0;
+
+	return check_submodule_move_head(ce, old_sha1,
+					 oid_to_hex(&ce->oid), o);
 }
 
 static int verify_clean_subdirectory(const struct cache_entry *ce,
@@ -1578,9 +1664,15 @@ static int verify_absent_1(const struct cache_entry *ce,
 		path = xmemdupz(ce->name, len);
 		if (lstat(path, &st))
 			ret = error_errno("cannot stat '%s'", path);
-		else
-			ret = check_ok_to_remove(path, len, DT_UNKNOWN, NULL,
-						 &st, error_type, o);
+		else {
+			if (submodule_from_ce(ce))
+				ret = check_submodule_move_head(ce,
+								oid_to_hex(&ce->oid),
+								NULL, o);
+			else
+				ret = check_ok_to_remove(path, len, DT_UNKNOWN, NULL,
+							 &st, error_type, o);
+		}
 		free(path);
 		return ret;
 	} else if (lstat(ce->name, &st)) {
@@ -1588,6 +1680,10 @@ static int verify_absent_1(const struct cache_entry *ce,
 			return error_errno("cannot stat '%s'", ce->name);
 		return 0;
 	} else {
+		if (submodule_from_ce(ce))
+			return check_submodule_move_head(ce, oid_to_hex(&ce->oid),
+							 NULL, o);
+
 		return check_ok_to_remove(ce->name, ce_namelen(ce),
 					  ce_to_dtype(ce), ce, &st,
 					  error_type, o);
@@ -1643,6 +1739,15 @@ static int merged_entry(const struct cache_entry *ce,
 			return -1;
 		}
 		invalidate_ce_path(merge, o);
+
+		if (submodule_from_ce(ce)) {
+			int ret = check_submodule_move_head(ce, NULL,
+							    oid_to_hex(&ce->oid),
+							    o);
+			if (ret)
+				return ret;
+		}
+
 	} else if (!(old->ce_flags & CE_CONFLICTED)) {
 		/*
 		 * See if we can re-use the old CE directly?
@@ -1663,6 +1768,14 @@ static int merged_entry(const struct cache_entry *ce,
 			update |= old->ce_flags & (CE_SKIP_WORKTREE | CE_NEW_SKIP_WORKTREE);
 			invalidate_ce_path(old, o);
 		}
+
+		if (submodule_from_ce(ce)) {
+			int ret = check_submodule_move_head(ce, oid_to_hex(&old->oid),
+							    oid_to_hex(&ce->oid),
+							    o);
+			if (ret)
+				return ret;
+		}
 	} else {
 		/*
 		 * Previously unmerged entry left as an existence
diff --git a/unpack-trees.h b/unpack-trees.h
index 36a73a6d00..6c48117b84 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -21,6 +21,7 @@ enum unpack_trees_error_types {
 	ERROR_SPARSE_NOT_UPTODATE_FILE,
 	ERROR_WOULD_LOSE_ORPHANED_OVERWRITTEN,
 	ERROR_WOULD_LOSE_ORPHANED_REMOVED,
+	ERROR_WOULD_LOSE_SUBMODULE,
 	NB_UNPACK_TREES_ERROR_TYPES
 };
 
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 17/19] entry.c: create submodules when interesting

[Stefan Beller]

When a submodule is introduced with a new revision
we need to create the submodule in the worktree as well.
As 'submodule_move_head' handles edge cases, all we have
to do is call it from within the function that creates
new files in the working tree for workingtree operations.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 entry.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/entry.c b/entry.c
index c6eea240b6..d2b512da90 100644
--- a/entry.c
+++ b/entry.c
@@ -2,6 +2,7 @@
 #include "blob.h"
 #include "dir.h"
 #include "streaming.h"
+#include "submodule.h"
 
 static void create_directories(const char *path, int path_len,
 			       const struct checkout *state)
@@ -146,6 +147,7 @@ static int write_entry(struct cache_entry *ce,
 	unsigned long size;
 	size_t wrote, newsize = 0;
 	struct stat st;
+	const struct submodule *sub;
 
 	if (ce_mode_s_ifmt == S_IFREG) {
 		struct stream_filter *filter = get_stream_filter(ce->name,
@@ -203,6 +205,10 @@ static int write_entry(struct cache_entry *ce,
 			return error("cannot create temporary submodule %s", path);
 		if (mkdir(path, 0777) < 0)
 			return error("cannot create submodule directory %s", path);
+		sub = submodule_from_ce(ce);
+		if (sub)
+			return submodule_move_head(ce->name,
+				NULL, oid_to_hex(&ce->oid), SUBMODULE_MOVE_HEAD_FORCE);
 		break;
 	default:
 		return error("unknown file mode for %s in index", path);
@@ -259,7 +265,31 @@ int checkout_entry(struct cache_entry *ce,
 	strbuf_add(&path, ce->name, ce_namelen(ce));
 
 	if (!check_path(path.buf, path.len, &st, state->base_dir_len)) {
+		const struct submodule *sub;
 		unsigned changed = ce_match_stat(ce, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
+		/*
+		 * Needs to be checked before !changed returns early,
+		 * as the possibly empty directory was not changed
+		 */
+		sub = submodule_from_ce(ce);
+		if (sub) {
+			int err;
+			if (!is_submodule_populated_gently(ce->name, &err)) {
+				struct stat sb;
+				if (lstat(ce->name, &sb))
+					die(_("could not stat file '%s'"), ce->name);
+				if (!(st.st_mode & S_IFDIR))
+					unlink_or_warn(ce->name);
+
+				return submodule_move_head(ce->name,
+					NULL, oid_to_hex(&ce->oid),
+					SUBMODULE_MOVE_HEAD_FORCE);
+			} else
+				return submodule_move_head(ce->name,
+					"HEAD", oid_to_hex(&ce->oid),
+					SUBMODULE_MOVE_HEAD_FORCE);
+		}
+
 		if (!changed)
 			return 0;
 		if (!state->force) {
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 18/19] builtin/checkout: add --recurse-submodules switch

[Stefan Beller]

This exposes a flag to recurse into submodules
in builtin/checkout making use of the code implemented
in prior patches.

A new failure mode is introduced in the submodule
update library, as the directory/submodule conflict
is not solved in prior patches.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/git-checkout.txt |  7 +++++++
 builtin/checkout.c             | 28 ++++++++++++++++++++++++++++
 t/lib-submodule-update.sh      | 26 +++++++++++++++++++++-----
 t/t2013-checkout-submodule.sh  |  6 ++++++
 4 files changed, 62 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 8e2c0662dd..d6399c0af8 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -256,6 +256,13 @@ section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
 	out anyway. In other words, the ref can be held by more than one
 	worktree.
 
+--[no-]recurse-submodules::
+	Using --recurse-submodules will update the content of all initialized
+	submodules according to the commit recorded in the superproject. If
+	local modifications in a submodule would be overwritten the checkout
+	will fail unless `-f` is used. If nothing (or --no-recurse-submodules)
+	is used, the work trees of submodules will not be updated.
+
 <branch>::
 	Branch to checkout; if it refers to a branch (i.e., a name that,
 	when prepended with "refs/heads/", is a valid ref), then that
diff --git a/builtin/checkout.c b/builtin/checkout.c
index f174f50303..e9c5fcfaf8 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -21,12 +21,31 @@
 #include "submodule-config.h"
 #include "submodule.h"
 
+static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
+
 static const char * const checkout_usage[] = {
 	N_("git checkout [<options>] <branch>"),
 	N_("git checkout [<options>] [<branch>] -- <file>..."),
 	NULL,
 };
 
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
+{
+	if (unset) {
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
 struct checkout_opts {
 	int patch_mode;
 	int quiet;
@@ -1163,6 +1182,9 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 				N_("second guess 'git checkout <no-such-branch>'")),
 		OPT_BOOL(0, "ignore-other-worktrees", &opts.ignore_other_worktrees,
 			 N_("do not check if another worktree is holding the given ref")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules },
 		OPT_BOOL(0, "progress", &opts.show_progress, N_("force progress reporting")),
 		OPT_END(),
 	};
@@ -1193,6 +1215,12 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
 	}
 
+	if (recurse_submodules != RECURSE_SUBMODULES_OFF) {
+		git_config(submodule_config, NULL);
+		if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT)
+			set_config_update_recurse_submodules(recurse_submodules);
+	}
+
 	if ((!!opts.new_branch + !!opts.new_branch_force + !!opts.new_orphan_branch) > 1)
 		die(_("-b, -B and --orphan are mutually exclusive"));
 
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index ae560dc95c..4e775a38b6 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -782,6 +782,16 @@ test_submodule_forced_switch () {
 
 test_submodule_switch_recursing () {
 	command="$1"
+	RESULTDS=success
+	if test "$KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS" = 1
+	then
+		RESULTDS=failure
+	fi
+	RESULTR=success
+	if test "$KNOWN_FAILURE_SUBMODULE_RECURSIVE_NESTED" = 1
+	then
+		RESULTR=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -891,7 +901,7 @@ test_submodule_switch_recursing () {
 	'
 	# Replacing a submodule with files in a directory must succeeds
 	# when the submodule is clean
-	test_expect_success "$command: replace submodule with a directory" '
+	test_expect_$RESULTDS "$command: replace submodule with a directory" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -903,7 +913,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... absorbing a .git directory.
-	test_expect_success "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
+	test_expect_$RESULTDS "$command: replace submodule containing a .git directory with a directory must absorb the git dir" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -931,7 +941,7 @@ test_submodule_switch_recursing () {
 	'
 
 	# ... must check its local work tree for untracked files
-	test_expect_success "$command: replace submodule with a file must fail with untracked files" '
+	test_expect_$RESULTDS "$command: replace submodule with a file must fail with untracked files" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
@@ -987,7 +997,8 @@ test_submodule_switch_recursing () {
 		)
 	'
 
-	test_expect_success "$command: modified submodule updates submodule recursively" '
+	# recursing deeper than one level doesn't work yet.
+	test_expect_$RESULTR "$command: modified submodule updates submodule recursively" '
 		prolog &&
 		reset_work_tree_to_interested add_nested_sub &&
 		(
@@ -1006,6 +1017,11 @@ test_submodule_switch_recursing () {
 # the superproject as well as the submodule is allowed.
 test_submodule_forced_switch_recursing () {
 	command="$1"
+	RESULT=success
+	if test "$KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS" = 1
+	then
+		RESULT=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear creates empty dir ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -1151,7 +1167,7 @@ test_submodule_forced_switch_recursing () {
 	'
 
 	# ... but stops for untracked files that would be lost
-	test_expect_success "$command: replace submodule with a file" '
+	test_expect_$RESULT "$command: replace submodule with a file stops for untracked files" '
 		prolog &&
 		reset_work_tree_to_interested add_sub1 &&
 		(
diff --git a/t/t2013-checkout-submodule.sh b/t/t2013-checkout-submodule.sh
index 6847f75822..e8f70b806f 100755
--- a/t/t2013-checkout-submodule.sh
+++ b/t/t2013-checkout-submodule.sh
@@ -63,6 +63,12 @@ test_expect_success '"checkout <submodule>" honors submodule.*.ignore from .git/
 	! test -s actual
 '
 
+KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+KNOWN_FAILURE_SUBMODULE_RECURSIVE_NESTED=1
+test_submodule_switch_recursing "git checkout --recurse-submodules"
+
+test_submodule_forced_switch_recursing "git checkout -f --recurse-submodules"
+
 test_submodule_switch "git checkout"
 
 test_submodule_forced_switch "git checkout -f"
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

[PATCH 19/19] builtin/read-tree: add --recurse-submodules switch

[Stefan Beller]

A new known failure mode is introduced[1], which is actually not
a failure but a feature in read-tree. Unlike checkout for which
the recursive submodule tests were originally written, read-tree does
warn about ignored untracked files that would be overwritten.
For the sake of keeping the test library for submodules generic, just
mark the test as a failure.

[1] KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/git-read-tree.txt |  6 ++++++
 builtin/read-tree.c             | 29 +++++++++++++++++++++++++++++
 t/lib-submodule-update.sh       |  7 ++++++-
 t/t1013-read-tree-submodule.sh  |  8 ++++++++
 4 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt
index fa1d557e5b..ed9d63ef4a 100644
--- a/Documentation/git-read-tree.txt
+++ b/Documentation/git-read-tree.txt
@@ -115,6 +115,12 @@ OPTIONS
 	directories the index file and index output file are
 	located in.
 
+--[no-]recurse-submodules::
+	Using --recurse-submodules will update the content of all initialized
+	submodules according to the commit recorded in the superproject by
+	calling read-tree recursively, also setting the submodules HEAD to be
+	detached at that commit.
+
 --no-sparse-checkout::
 	Disable sparse checkout support even if `core.sparseCheckout`
 	is true.
diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 8ba64bc785..23e212ee8c 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -15,10 +15,13 @@
 #include "builtin.h"
 #include "parse-options.h"
 #include "resolve-undo.h"
+#include "submodule.h"
+#include "submodule-config.h"
 
 static int nr_trees;
 static int read_empty;
 static struct tree *trees[MAX_UNPACK_TREES];
+static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 
 static int list_tree(unsigned char *sha1)
 {
@@ -96,6 +99,23 @@ static int debug_merge(const struct cache_entry * const *stages,
 	return 0;
 }
 
+static int option_parse_recurse_submodules(const struct option *opt,
+					   const char *arg, int unset)
+{
+	if (unset) {
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
 static struct lock_file lock_file;
 
 int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
@@ -137,6 +157,9 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 			 N_("skip applying sparse checkout filter")),
 		OPT_BOOL(0, "debug-unpack", &opts.debug_unpack,
 			 N_("debug unpack-trees")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules },
 		OPT_END()
 	};
 
@@ -152,6 +175,12 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 
 	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
 
+	if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT) {
+		gitmodules_config();
+		git_config(submodule_config, NULL);
+		set_config_update_recurse_submodules(RECURSE_SUBMODULES_ON);
+	}
+
 	prefix_set = opts.prefix ? 1 : 0;
 	if (1 < opts.merge + opts.reset + prefix_set)
 		die("Which one? -m, --reset, or --prefix?");
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 4e775a38b6..fb4f7b014e 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -792,6 +792,11 @@ test_submodule_switch_recursing () {
 	then
 		RESULTR=failure
 	fi
+	RESULTOI=success
+	if test "$KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED" = 1
+	then
+		RESULTOI=failure
+	fi
 	######################### Appearing submodule #########################
 	# Switching to a commit letting a submodule appear checks it out ...
 	test_expect_success "$command: added submodule is checked out" '
@@ -832,7 +837,7 @@ test_submodule_switch_recursing () {
 		)
 	'
 	# ... but an ignored file is fine.
-	test_expect_success "$command: added submodule removes an untracked ignored file" '
+	test_expect_$RESULTOI "$command: added submodule removes an untracked ignored file" '
 		test_when_finished "rm submodule_update/.git/info/exclude" &&
 		prolog &&
 		reset_work_tree_to_interested no_submodule &&
diff --git a/t/t1013-read-tree-submodule.sh b/t/t1013-read-tree-submodule.sh
index 20526aed34..de1ba02dc5 100755
--- a/t/t1013-read-tree-submodule.sh
+++ b/t/t1013-read-tree-submodule.sh
@@ -5,6 +5,14 @@ test_description='read-tree can handle submodules'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-submodule-update.sh
 
+KNOWN_FAILURE_SUBMODULE_RECURSIVE_NESTED=1
+KNOWN_FAILURE_DIRECTORY_SUBMODULE_CONFLICTS=1
+KNOWN_FAILURE_SUBMODULE_OVERWRITE_IGNORED_UNTRACKED=1
+
+test_submodule_switch_recursing "git read-tree --recurse-submodules -u -m"
+
+test_submodule_forced_switch_recursing "git read-tree --recurse-submodules -u --reset"
+
 test_submodule_switch "git read-tree -u -m"
 
 test_submodule_forced_switch "git read-tree -u --reset"
-- 
2.12.0.rc1.49.g0cfd38c5f6.dirty

Re: [PATCHv9 00/19] Checkout aware of Submodules!

[Brandon Williams]

On 03/14, Stefan Beller wrote:
> previous work:
> https://public-inbox.org/git/20170309221543.15897-1-sbeller@google.com/
> 
> v9:
>  * inderdiff to current origin/sb/checkout-recurse-submodules below
>  * fixed a '\' that was violating the style guide.
>  * reordered the patches, such that
>    -> the first two patches are Valerys series and could go on its own as
>       a cleanup  
>    -> added a new patch "submodule.c: get_super_prefix_or_empty" to
>       have cleaner code.
>  * split up the error conditions in the test lib for readability

Changes looks sensible to me.

-- 
Brandon Williams