[RFC] git-submodule update: Add --commit option

["W. Trevor King" <wking@tremily.us>]

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This option triggers automatic commits when `submodule update` changes
any gitlinked submodule SHA-1s.  The commit message contains a
`shortlog` summary of the changes for each changed submodule.
---

On Tue, Nov 27, 2012 at 07:51:42PM +0100, Heiko Voigt wrote:
> BTW, I am more and more convinced that an automatically manufactured
> commit on update with --branch should be the default. What do other
> think? Sascha raised a concern that he would not want this, but as far as
> I understood he let the CI-server do that so I see no downside to
> natively adding that to git. People who want to manually craft those
> commits can still amend the generated commit. Since this is all about
> helping people keeping their submodules updated why not go the full way?

Here's a first pass (without documentation) for automatic commits on
submodule updates.  There have been a number of requests for
automatically-committed submodule updates due to submodule upstreams.
This patch shows how you can do that (if applied with my `submodule
update --remote` series), and reuse the same logic to automatically
commit changes due to local submodule changes (as shown here in the
new test).

I think the logic is pretty good, but the implementation is pretty
ugly due to POSIX shell variable limitations.  I'm basically trying to
pass an array of [(name, sm_path, sha1, subsha1), ...] into
commit_changes().  I though about perling-out in commit_changes(), but
I lack sufficient perl-fu to know how to tie clear_local_git_env, cd,
and shortlog up in a single open2 call.  If anyone can give me some
implementation pointers, that would be very helpful.

This is against v1.8.0 (without my --remote series).  To apply on top
of the --remote series, you'd have to save the original gitlinked
$sha1 and use that original value when constructing changed_modules.
I can attach this to the end of the --remote series if desired, but I
think this patch could also stand on its own.

Obviously this still needs documentation, etc., but I wanted feedback
on the implementation before I started digging into that.

Cheers,
Trevor

---
 git-submodule.sh            | 67 ++++++++++++++++++++++++++++++++++++++++++++-
 t/t7406-submodule-update.sh | 19 +++++++++++++
 2 files changed, 85 insertions(+), 1 deletion(-)

diff --git a/git-submodule.sh b/git-submodule.sh
index ab6b110..d9a59af 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -8,7 +8,7 @@ dashless=$(basename "$0" | sed -e 's/-/ /')
 USAGE="[--quiet] add [-b branch] [-f|--force] [--reference <repository>] [--] <repository> [<path>]
    or: $dashless [--quiet] status [--cached] [--recursive] [--] [<path>...]
    or: $dashless [--quiet] init [--] [<path>...]
-   or: $dashless [--quiet] update [--init] [-N|--no-fetch] [-f|--force] [--rebase] [--reference <repository>] [--merge] [--recursive] [--] [<path>...]
+   or: $dashless [--quiet] update [--init] [-N|--no-fetch] [-f|--force] [--commit] [--rebase] [--reference <repository>] [--merge] [--recursive] [--] [<path>...]
    or: $dashless [--quiet] summary [--cached|--files] [--summary-limit <n>] [commit] [--] [<path>...]
    or: $dashless [--quiet] foreach [--recursive] <command>
    or: $dashless [--quiet] sync [--] [<path>...]"
@@ -21,6 +21,7 @@ require_work_tree
 command=
 branch=
 force=
+commit=
 reference=
 cached=
 recursive=
@@ -240,6 +241,52 @@ module_clone()
 }
 
 #
+# Commit changed submodule gitlinks
+#
+# $1 = name-a;sha1-a;subsha1-a\n[name-b;sha1-b;subsha1-b\n...]
+#
+commit_changes()
+{
+	echo "commiting $1"
+	OIFS="$IFS"
+	IFS=";"
+	paths=$(echo "$1" |
+		while read name sm_path sha1 subsha1
+		do
+			echo "$sm_path"
+		done
+		)
+	names=$(echo "$1" |
+		while read name sm_path sha1 subsha1
+		do
+			printf ' %s' "$name"
+		done
+		)
+	summary="$(eval_gettext "Updated submodules:")$names"
+	body=$(echo "$1" |
+		while read name sm_path sha1 subsha1
+		do
+			if test "$name" = "$sm_path"
+			then
+				printf 'Changes to %s:\n\n' "$name"
+			else
+				printf 'Changes to %s (%s):\n\n' "$name" "$sm_path"
+			fi
+			(
+				clear_local_git_env
+				cd "$sm_path" &&
+				git shortlog "${sha1}..${subsha1}" ||
+				die "$(eval_gettext "Unable to generate shortlog in submodule path '\$sm_path'")"
+			)
+		done
+		)
+	IFS="$OIFS"
+	message="$(printf '%s\n\n%s\n' "$summary" "$body")"
+	echo "message: [$message]"
+	git commit -m "$message" $paths
+}
+
+#
 # Add a new submodule to the working tree, .gitmodules and the index
 #
 # $@ = repo path
@@ -515,6 +562,9 @@ cmd_update()
 		-f|--force)
 			force=$1
 			;;
+		--commit)
+			commit=1
+			;;
 		-r|--rebase)
 			update="rebase"
 			;;
@@ -557,6 +607,7 @@ cmd_update()
 	fi
 
 	cloned_modules=
+	changed_modules=
 	module_list "$@" | {
 	err=
 	while read mode sha1 stage sm_path
@@ -660,6 +711,15 @@ Maybe you want to use 'update --init'?")"
 				err="${err};$die_msg"
 				continue
 			fi
+
+			subsha1=$(clear_local_git_env; cd "$sm_path" &&
+				git rev-parse --verify HEAD) ||
+			die "$(eval_gettext "Unable to find new revision in submodule path '\$sm_path'")"
+
+			if test "$subsha1" != "$sha1"
+			then
+				changed_modules=$(printf '%s%s\n' "$changed_modules" "$name;$sm_path;$sha1;$subsha1")
+			fi
 		fi
 
 		if test -n "$recursive"
@@ -680,6 +740,11 @@ Maybe you want to use 'update --init'?")"
 		fi
 	done
 
+	if test -z "$err" -a -n "$commit" -a -n "$changed_modules"
+	then
+		commit_changes "$changed_modules"
+	fi
+
 	if test -n "$err"
 	then
 		OIFS=$IFS
diff --git a/t/t7406-submodule-update.sh b/t/t7406-submodule-update.sh
index 1542653..4c8bb5d 100755
--- a/t/t7406-submodule-update.sh
+++ b/t/t7406-submodule-update.sh
@@ -163,6 +163,25 @@ test_expect_success 'submodule update --merge staying on master' '
 	)
 '
 
+test_expect_success 'submodule update --commit --rebase should commit gitlink changes' '
+	(cd super/submodule &&
+	 git reset --hard HEAD~1 &&
+	 echo "local change" > local-file &&
+	 git add local-file &&
+	 test_tick &&
+	 git commit -m "local change"
+	) &&
+	(cd super &&
+	 git submodule update --commit --rebase submodule &&
+	 test "$(git log -1 --oneline)" = "bbdbe2d Updated submodules: submodule"
+	) &&
+	(cd submodule &&
+	 git remote add super-submodule ../super/submodule &&
+	 git pull super-submodule master
+	) &&
+  test "a" = "b"
+'
+
 test_expect_success 'submodule update - rebase in .git/config' '
 	(cd super &&
 	 git config submodule.submodule.update rebase
-- 
1.8.0.1.gaaf2ac7.dirty

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