path: implement common_dir handling in git_pathdup_submodule()

When submodule is a linked worktree, "git diff --submodule" and other
calls which directly access the submodule's object database do not correctly
calculate its path. Fix it by changing the git_pathdup_submodule() behavior,
to use either common or per-worktree directory.

Do it similarly as for parent repository, but ignore the GIT_COMMON_DIR
environment variable, because it would mean common directory for the parent
repository and does not make sense for submodule.

Also add test for functionality which uses this call.

Signed-off-by: Max Kirillov <max@max630.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/setup.c b/setup.c
index a17c51e..e41e5e1 100644
--- a/setup.c
+++ b/setup.c
@@ -229,14 +229,21 @@ void verify_non_filename(const char *prefix, const char *arg)
 
 int get_common_dir(struct strbuf *sb, const char *gitdir)
 {
+	const char *git_env_common_dir = getenv(GIT_COMMON_DIR_ENVIRONMENT);
+	if (git_env_common_dir) {
+		strbuf_addstr(sb, git_env_common_dir);
+		return 1;
+	} else {
+		return get_common_dir_noenv(sb, gitdir);
+	}
+}
+
+int get_common_dir_noenv(struct strbuf *sb, const char *gitdir)
+{
 	struct strbuf data = STRBUF_INIT;
 	struct strbuf path = STRBUF_INIT;
-	const char *git_common_dir = getenv(GIT_COMMON_DIR_ENVIRONMENT);
 	int ret = 0;
-	if (git_common_dir) {
-		strbuf_addstr(sb, git_common_dir);
-		return 1;
-	}
+
 	strbuf_addf(&path, "%s/commondir", gitdir);
 	if (file_exists(path.buf)) {
 		if (strbuf_read_file(&data, path.buf, 0) <= 0)