[PATCH v4 4/4] submodule: record superproject gitdir during 'update'

[Emily Shaffer <emilyshaffer@google.com>]

A recorded hint path to the superproject's gitdir might be added during
'git submodule add', but in some cases - like submodules which were
created before 'git submodule add' learned to record that info - it might
be useful to update the hint. Let's do it during 'git submodule
update', when we already have a handle to the superproject while calling
operations on the submodules.

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
---
 git-submodule.sh            | 14 ++++++++++++++
 t/t7406-submodule-update.sh | 12 ++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/git-submodule.sh b/git-submodule.sh
index 652861aa66..ec02eb5971 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -449,6 +449,20 @@ cmd_update()
 			;;
 		esac
 
+		# Cache a pointer to the superproject's gitdir. This may have
+		# changed, unless it's a fresh clone. Writes it to worktree
+		# if applicable, otherwise to local.
+		if test -z "$just_cloned"
+		then
+			sm_gitdir="$(git -C "$sm_path" rev-parse --absolute-git-dir)"
+			relative_gitdir="$(git rev-parse --path-format=relative \
+							 --prefix "${sm_gitdir}" \
+							 --git-dir)"
+
+			git -C "$sm_path" config --worktree \
+				submodule.superprojectgitdir "$relative_gitdir"
+		fi
+
 		if test -n "$recursive"
 		then
 			(
diff --git a/t/t7406-submodule-update.sh b/t/t7406-submodule-update.sh
index 11cccbb333..7fd5741a5a 100755
--- a/t/t7406-submodule-update.sh
+++ b/t/t7406-submodule-update.sh
@@ -1061,4 +1061,16 @@ test_expect_success 'submodule update --quiet passes quietness to fetch with a s
 	)
 '
 
+test_expect_success 'submodule update adds superproject gitdir to older repos' '
+	(cd super &&
+	 git -C submodule config --unset submodule.superprojectGitdir &&
+	 git submodule update &&
+	 test-tool path-utils relative_path \
+		"$(git rev-parse --absolute-git-dir)" \
+		"$(git -C submodule rev-parse --absolute-git-dir)" >expect &&
+	 git -C submodule config submodule.superprojectGitdir >actual &&
+	 test_cmp expect actual
+	)
+'
+
 test_done
-- 
2.33.0.1079.g6e70778dc9-goog