submodule: add gitdir path config override

This adds the ability to override gitdir paths via config files
(not .gitmodules) such that the encoding scheme (or plain text
name if the encoding extension is disabled) can be changed via
config entries.

These entries are not added by default for all submodules: they
should be used on an as-needed basis.

A new test and a helper are added. The helper will also be used
in further tests exercising gitdir encoding functionality.

Based-on-patch-by: Brandon Williams <[email protected]>
Signed-off-by: Adrian Ratiu <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: 10ne1

Documentation/config/submodule.adoc

@@ -52,6 +52,10 @@ submodule.<name>.active::
 	submodule.active config option. See linkgit:gitsubmodules[7] for
 	details.
 
+submodule.<name>.gitdir::
+	This option sets the gitdir path for submodule <name>, allowing users
+	to override the default path or change the default path name encoding.
+
 submodule.active::
 	A repeated field which contains a pathspec used to match against a
 	submodule's path to determine if the submodule is of interest to git

builtin/submodule--helper.c

@@ -1214,6 +1214,22 @@ static int module_summary(int argc, const char **argv, const char *prefix,
 	return ret;
 }
 
+static int module_gitdir(int argc, const char **argv, const char *prefix UNUSED,
+			 struct repository *repo)
+{
+	struct strbuf gitdir = STRBUF_INIT;
+
+	if (argc != 2)
+		usage(_("git submodule--helper gitdir <name>"));
+
+	submodule_name_to_gitdir(&gitdir, repo, argv[1]);
+
+	printf("%s\n", gitdir.buf);
+
+	strbuf_release(&gitdir);
+	return 0;
+}
+
 struct sync_cb {
 	const char *prefix;
 	const char *super_prefix;
@@ -3597,6 +3613,7 @@ int cmd_submodule__helper(int argc,
 		NULL
 	};
 	struct option options[] = {
+		OPT_SUBCOMMAND("gitdir", &fn, module_gitdir),
 		OPT_SUBCOMMAND("clone", &fn, module_clone),
 		OPT_SUBCOMMAND("add", &fn, module_add),
 		OPT_SUBCOMMAND("update", &fn, module_update),

submodule.c

@@ -2604,6 +2604,18 @@ void submodule_name_to_gitdir(struct strbuf *buf, struct repository *r,
 	 * administrators can explicitly set. Nothing has been decided,
 	 * so for now, just append the name at the end of the path.
 	 */
+	char *gitdir_path, *key;
+
+	/* Allow config override. */
+	key = xstrfmt("submodule.%s.gitdirpath", submodule_name);
+	if (!repo_config_get_string(r, key, &gitdir_path)) {
+		strbuf_addstr(buf, gitdir_path);
+		free(key);
+		free(gitdir_path);
+		return;
+	}
+	free(key);
+
 	repo_git_path_append(r, buf, "modules/");
 	strbuf_addstr(buf, submodule_name);
 }

t/lib-verify-submodule-gitdir-path.sh

@@ -0,0 +1,20 @@
+# Helper to verify if repo $1 contains a submodule named $2 with gitdir path $3
+
+# This does not check filesystem existence. That is done in submodule.c via the
+# submodule_name_to_gitdir() API which this helper ends up calling. The gitdirs
+# might or might not exist (e.g. when adding a new submodule), so this only
+# checks the expected configuration path, which might be overridden by the user.
+
+verify_submodule_gitdir_path() {
+	repo="$1" &&
+	name="$2" &&
+	path="$3" &&
+	(
+		cd "$repo" &&
+		cat >expect <<-EOF &&
+			$(git rev-parse --git-common-dir)/$path
+		EOF
+		git submodule--helper gitdir "$name" >actual &&
+		test_cmp expect actual
+	)
+}

t/t7400-submodule-basic.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-verify-submodule-gitdir-path.sh
 
 test_expect_success 'setup - enable local submodules' '
 	git config --global protocol.file.allow always
@@ -1505,4 +1506,12 @@ test_expect_success 'submodule add fails when name is reused' '
 	)
 '
 
+test_expect_success 'submodule helper gitdir config overrides' '
+	verify_submodule_gitdir_path test-submodule child modules/child &&
+	test_config -C test-submodule submodule.child.gitdirpath ".git/modules/custom-child" &&
+	verify_submodule_gitdir_path test-submodule child modules/custom-child &&
+	test_unconfig -C test-submodule submodule.child.gitdirpath &&
+	verify_submodule_gitdir_path test-submodule child modules/child
+'
+
 test_done

t/t9902-completion.sh

@@ -3053,6 +3053,7 @@ test_expect_success 'git config set - variable name - __git_compute_second_level
 	submodule.sub.fetchRecurseSubmodules Z
 	submodule.sub.ignore Z
 	submodule.sub.active Z
+	submodule.sub.gitdir Z
 	EOF
 '