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>

cache.h

@@ -443,6 +443,7 @@ extern char *get_object_directory(void);
 extern char *get_index_file(void);
 extern char *get_graft_file(void);
 extern int set_git_dir(const char *path);
+extern int get_common_dir_noenv(struct strbuf *sb, const char *gitdir);
 extern int get_common_dir(struct strbuf *sb, const char *gitdir);
 extern const char *get_git_namespace(void);
 extern const char *strip_namespace(const char *namespaced_ref);

path.c

@@ -98,7 +98,7 @@ static const char *common_list[] = {
 	NULL
 };
 
-static void update_common_dir(struct strbuf *buf, int git_dir_len)
+static void update_common_dir(struct strbuf *buf, int git_dir_len, const char *common_dir)
 {
 	char *base = buf->buf + git_dir_len;
 	const char **p;
@@ -115,12 +115,16 @@ static void update_common_dir(struct strbuf *buf, int git_dir_len)
 			path++;
 			is_dir = 1;
 		}
+
+		if (!common_dir)
+			common_dir = get_git_common_dir();
+
 		if (is_dir && dir_prefix(base, path)) {
-			replace_dir(buf, git_dir_len, get_git_common_dir());
+			replace_dir(buf, git_dir_len, common_dir);
 			return;
 		}
 		if (!is_dir && !strcmp(base, path)) {
-			replace_dir(buf, git_dir_len, get_git_common_dir());
+			replace_dir(buf, git_dir_len, common_dir);
 			return;
 		}
 	}
@@ -160,7 +164,7 @@ static void adjust_git_path(struct strbuf *buf, int git_dir_len)
 	else if (git_db_env && dir_prefix(base, "objects"))
 		replace_dir(buf, git_dir_len + 7, get_object_directory());
 	else if (git_common_dir_env)
-		update_common_dir(buf, git_dir_len);
+		update_common_dir(buf, git_dir_len, NULL);
 }
 
 static void do_git_path(struct strbuf *buf, const char *fmt, va_list args)
@@ -228,6 +232,8 @@ static void do_submodule_path(struct strbuf *buf, const char *path,
 			      const char *fmt, va_list args)
 {
 	const char *git_dir;
+	struct strbuf git_submodule_common_dir = STRBUF_INIT;
+	struct strbuf git_submodule_dir = STRBUF_INIT;
 
 	strbuf_addstr(buf, path);
 	if (buf->len && buf->buf[buf->len - 1] != '/')
@@ -240,9 +246,17 @@ static void do_submodule_path(struct strbuf *buf, const char *path,
 		strbuf_addstr(buf, git_dir);
 	}
 	strbuf_addch(buf, '/');
+	strbuf_addstr(&git_submodule_dir, buf->buf);
 
 	strbuf_vaddf(buf, fmt, args);
+
+	if (get_common_dir_noenv(&git_submodule_common_dir, git_submodule_dir.buf))
+		update_common_dir(buf, git_submodule_dir.len, git_submodule_common_dir.buf);
+
 	strbuf_cleanup_path(buf);
+
+	strbuf_release(&git_submodule_dir);
+	strbuf_release(&git_submodule_common_dir);
 }
 
 char *git_pathdup_submodule(const char *path, const char *fmt, ...)

setup.c

@@ -228,15 +228,22 @@ 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)

t/t7410-submodule-checkout-to.sh

@@ -47,4 +47,14 @@ test_expect_success 'checkout main and initialize independed clones' \
 test_expect_success 'can see submodule diffs after independed cloning' \
     '(cd fully_cloned_submodule/main && git diff --submodule master"^!" | grep "file1 updated")'
 
+test_expect_success 'checkout sub manually' \
+    'mkdir linked_submodule &&
+    (cd clone/main &&
+	git worktree add "$base_path/linked_submodule/main" "$rev1_hash_main") &&
+    (cd clone/main/sub &&
+	git worktree add "$base_path/linked_submodule/main/sub" "$rev1_hash_sub")'
+
+test_expect_success 'can see submodule diffs after manual checkout of linked submodule' \
+    '(cd linked_submodule/main && git diff --submodule master"^!" | grep "file1 updated")'
+
 test_done