[RFC PATCH 2/2] submodule: add test mode for checking absence of "superProjectGitDir"

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Add a GIT_TEST_SUBMODULE_CACHE_SUPERPROJECT_DIR=false test mode to
assert what happens if "submodule.superProjectGitDir" is absent or
missing, this checks if the "fallback" codepath in
get_superproject_working_tree() is equivalent to the config lookup.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 ci/run-build-and-tests.sh          |  1 +
 git-submodule.sh                   |  2 +-
 submodule.c                        |  7 +++++++
 t/lib-submodule-superproject.sh    | 24 ++++++++++++++++++++++++
 t/t7406-submodule-update.sh        |  9 ++++-----
 t/t7412-submodule-absorbgitdirs.sh | 19 ++++++-------------
 6 files changed, 43 insertions(+), 19 deletions(-)
 create mode 100644 t/lib-submodule-superproject.sh

diff --git a/ci/run-build-and-tests.sh b/ci/run-build-and-tests.sh
index cc62616d806..5132a210057 100755
--- a/ci/run-build-and-tests.sh
+++ b/ci/run-build-and-tests.sh
@@ -33,6 +33,7 @@ linux-gcc)
 	export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=master
 	export GIT_TEST_WRITE_REV_INDEX=1
 	export GIT_TEST_CHECKOUT_WORKERS=2
+	export GIT_TEST_SUBMODULE_CACHE_SUPERPROJECT_DIR=false
 	make test
 	;;
 linux-clang)
diff --git a/git-submodule.sh b/git-submodule.sh
index 7c247bee7f6..2b423ee05bc 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -453,7 +453,7 @@ cmd_update()
 		# changed, unless it's a fresh clone. Write to worktree if
 		# applicable, and point to superproject's worktree gitdir if
 		# applicable.
-		if test -z "$just_cloned"
+		if test -z "$just_cloned" && test "$GIT_TEST_SUBMODULE_CACHE_SUPERPROJECT_DIR" != "false"
 		then
 			sm_gitdir="$(git -C "$sm_path" rev-parse --absolute-git-dir)"
 			relative_gitdir="$(git rev-parse --path-format=relative \
diff --git a/submodule.c b/submodule.c
index ad95cdda07d..f0411a320a8 100644
--- a/submodule.c
+++ b/submodule.c
@@ -2143,6 +2143,9 @@ static void relocate_single_git_dir_into_superproject(const char *path)
 	if (!git_configset_get_bool(&sub_cs, "extensions.worktreeConfig", &tmp))
 		strbuf_addstr(&config_path, ".worktree");
 
+	if (!git_env_bool("GIT_TEST_SUBMODULE_CACHE_SUPERPROJECT_DIR", 1))
+		goto fallback;
+
 	git_config_set_in_file(config_path.buf, "submodule.superprojectGitdir",
 			       relative_path(absolute_path(get_git_dir()),
 					     real_new_git_dir, &sb));
@@ -2150,6 +2153,8 @@ static void relocate_single_git_dir_into_superproject(const char *path)
 	git_configset_clear(&sub_cs);
 	strbuf_release(&config_path);
 	strbuf_release(&sb);
+
+fallback:
 	free(old_git_dir);
 	free(real_old_git_dir);
 	free(real_new_git_dir);
@@ -2332,6 +2337,8 @@ int get_superproject_working_tree(struct strbuf *buf)
 	const char *wt_prefix = "worktree ";
 	int rc = 0;
 
+	if (!git_env_bool("GIT_TEST_SUBMODULE_CACHE_SUPERPROJECT_DIR", 1))
+		goto fallback;
 
 	/* Do we know we have a superproject? */
 	if (git_config_get_string("submodule.superprojectgitdir", &super_gitdir))
diff --git a/t/lib-submodule-superproject.sh b/t/lib-submodule-superproject.sh
new file mode 100644
index 00000000000..4d49dd3782e
--- /dev/null
+++ b/t/lib-submodule-superproject.sh
@@ -0,0 +1,24 @@
+#!/bin/sh
+
+test_lazy_prereq SUBMODULE_CACHE_SUPERPROJECT_DIR '
+	test_bool_env GIT_TEST_SUBMODULE_CACHE_SUPERPROJECT_DIR true
+'
+
+test_cmp_submodule_superprojectgitdir () {
+	if ! test_have_prereq SUBMODULE_CACHE_SUPERPROJECT_DIR
+	then
+		return 0
+	fi
+
+	git -C "$1" config submodule.superprojectGitDir >actual &&
+	test_cmp expect actual
+}
+
+test_file_not_empty_superprojectgitdir () {
+	if ! test_have_prereq SUBMODULE_CACHE_SUPERPROJECT_DIR
+	then
+		return 0
+	fi
+
+	test_file_not_empty "$(git -C $1 rev-parse --absolute-git-dir)/$2"
+}
diff --git a/t/t7406-submodule-update.sh b/t/t7406-submodule-update.sh
index 01e1acaf300..f362f8d0ef0 100755
--- a/t/t7406-submodule-update.sh
+++ b/t/t7406-submodule-update.sh
@@ -13,6 +13,7 @@ GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-submodule-superproject.sh
 
 
 compare_head()
@@ -1068,8 +1069,7 @@ test_expect_success 'submodule update adds superproject gitdir to older repos' '
 	 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_cmp_submodule_superprojectgitdir submodule
 	)
 '
 
@@ -1081,10 +1081,9 @@ test_expect_success 'submodule update uses config.worktree if applicable' '
 	 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_cmp_submodule_superprojectgitdir submodule &&
 
-	 test_file_not_empty "$(git -C submodule rev-parse --absolute-git-dir)/config.worktree"
+	 test_file_not_empty_superprojectgitdir submodule config.worktree
 	)
 '
 
diff --git a/t/t7412-submodule-absorbgitdirs.sh b/t/t7412-submodule-absorbgitdirs.sh
index 5753f902687..6faab7e56e9 100755
--- a/t/t7412-submodule-absorbgitdirs.sh
+++ b/t/t7412-submodule-absorbgitdirs.sh
@@ -7,6 +7,7 @@ directory into the superproject.
 '
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-submodule-superproject.sh
 
 test_expect_success 'setup a real submodule' '
 	git init sub1 &&
@@ -38,9 +39,7 @@ test_expect_success 'absorb the git dir' '
 
 	test-tool path-utils relative_path "$superproject_gitdir" \
 		"$submodule_gitdir" >expect &&
-	git -C sub1 config submodule.superprojectGitDir >actual &&
-
-	test_cmp expect actual
+	test_cmp_submodule_superprojectgitdir sub1
 '
 
 test_expect_success 'absorbing does not fail for deinitialized submodules' '
@@ -78,9 +77,7 @@ test_expect_success 'absorb the git dir in a nested submodule' '
 
 	test-tool path-utils relative_path "$sub1_gitdir" "$sub1_nested_gitdir" \
 		>expect &&
-	git -C sub1/nested config submodule.superprojectGitDir >actual &&
-
-	test_cmp expect actual
+	test_cmp_submodule_superprojectgitdir sub1
 '
 
 test_expect_success 're-setup nested submodule' '
@@ -170,9 +167,7 @@ test_expect_success 'absorbgitdirs works when called from a superproject worktre
 
 	test-tool path-utils relative_path "$superproject_gitdir" \
 		"$submodule_gitdir" >expect &&
-	git -C sub4 config submodule.superprojectGitDir >actual &&
-
-	test_cmp expect actual
+	test_cmp_submodule_superprojectgitdir sub4
 	)
 '
 
@@ -199,12 +194,10 @@ test_expect_success 'absorbgitdirs works with a submodule with worktree config'
 
 	test-tool path-utils relative_path "$superproject_gitdir" \
 		"$submodule_gitdir" >expect &&
-	git -C sub5 config submodule.superprojectGitDir >actual &&
-
-	test_cmp expect actual &&
+	test_cmp_submodule_superprojectgitdir sub5 &&
 
 	# make sure the config went into the submodule config.worktree
-	test_file_not_empty "$submodule_gitdir/config.worktree"
+	test_file_not_empty_superprojectgitdir sub5 config.worktree
 	)
 '
 
-- 
2.34.0.796.g2c87ed6146a