[PATCH 10/10] builtin/fetch: check for submodule updates in any ref update

[Stefan Beller <sbeller@google.com>]

Gerrit, the code review tool, has a different workflow than our mailing
list based approach. Usually users upload changes to a Gerrit server and
continuous integration and testing happens by bots. Sometimes however a
user wants to checkout a change locally and look at it locally. For this
use case, Gerrit offers a command line snippet to copy and paste to your
terminal, which looks like

  git fetch https://<host>/gerrit refs/changes/<id> &&
  git checkout FETCH_HEAD

For Gerrit changes that contain changing submodule gitlinks, it would be
easy to extend both the fetch and checkout with the '--recurse-submodules'
flag, such that this command line snippet would produce the state of a
change locally.

However the functionality added in the previous patch, which would
ensure that we fetch the objects in the submodule that the gitlink pointed
at, only works for remote tracking branches so far, not for FETCH_HEAD.

Make sure that fetching a superproject to its FETCH_HEAD, also respects
the existence checks for objects in the submodule recursion.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/fetch.c             |  8 ++------
 t/t5526-fetch-submodules.sh | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 95c44bf6ff..f39012d7c2 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -700,8 +700,6 @@ static int update_local_ref(struct ref *ref,
 			what = _("[new ref]");
 		}
 
-		if (recurse_submodules != RECURSE_SUBMODULES_OFF)
-			check_for_new_submodule_commits(&ref->new_oid);
 		r = s_update_ref(msg, ref, 0);
 		format_display(display, r ? '!' : '*', what,
 			       r ? _("unable to update local ref") : NULL,
@@ -715,8 +713,6 @@ static int update_local_ref(struct ref *ref,
 		strbuf_add_unique_abbrev(&quickref, &current->object.oid, DEFAULT_ABBREV);
 		strbuf_addstr(&quickref, "..");
 		strbuf_add_unique_abbrev(&quickref, &ref->new_oid, DEFAULT_ABBREV);
-		if (recurse_submodules != RECURSE_SUBMODULES_OFF)
-			check_for_new_submodule_commits(&ref->new_oid);
 		r = s_update_ref("fast-forward", ref, 1);
 		format_display(display, r ? '!' : ' ', quickref.buf,
 			       r ? _("unable to update local ref") : NULL,
@@ -729,8 +725,6 @@ static int update_local_ref(struct ref *ref,
 		strbuf_add_unique_abbrev(&quickref, &current->object.oid, DEFAULT_ABBREV);
 		strbuf_addstr(&quickref, "...");
 		strbuf_add_unique_abbrev(&quickref, &ref->new_oid, DEFAULT_ABBREV);
-		if (recurse_submodules != RECURSE_SUBMODULES_OFF)
-			check_for_new_submodule_commits(&ref->new_oid);
 		r = s_update_ref("forced-update", ref, 1);
 		format_display(display, r ? '!' : '+', quickref.buf,
 			       r ? _("unable to update local ref") : _("forced update"),
@@ -826,6 +820,8 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 				ref->force = rm->peer_ref->force;
 			}
 
+			if (recurse_submodules != RECURSE_SUBMODULES_OFF)
+				check_for_new_submodule_commits(&rm->old_oid);
 
 			if (!strcmp(rm->name, "HEAD")) {
 				kind = "";
diff --git a/t/t5526-fetch-submodules.sh b/t/t5526-fetch-submodules.sh
index 5a75b57852..799785783f 100755
--- a/t/t5526-fetch-submodules.sh
+++ b/t/t5526-fetch-submodules.sh
@@ -631,4 +631,28 @@ test_expect_success "fetch new submodule commits on-demand outside standard refs
 	)
 '
 
+test_expect_success 'fetch new submodule commits on-demand in FETCH_HEAD' '
+	# depends on the previous test for setup
+
+	C=$(git -C submodule commit-tree -m "another change outside refs/heads" HEAD^{tree}) &&
+	git -C submodule update-ref refs/changes/1 $C &&
+	git update-index --cacheinfo 160000 $C submodule &&
+	test_tick &&
+
+	D=$(git -C sub1 commit-tree -m "another change outside refs/heads" HEAD^{tree}) &&
+	git -C sub1 update-ref refs/changes/2 $D &&
+	git update-index --cacheinfo 160000 $D sub1 &&
+
+	git commit -m "updated submodules outside of refs/heads" &&
+	E=$(git rev-parse HEAD) &&
+	git update-ref refs/changes/2 $E &&
+	(
+		cd downstream &&
+		git fetch --recurse-submodules origin refs/changes/2 &&
+		git -C submodule cat-file -t $C &&
+		git -C sub1 cat-file -t $D &&
+		git checkout --recurse-submodules FETCH_HEAD
+	)
+'
+
 test_done
-- 
2.19.0