clone: support 'clone --shared' from a worktree

When worktree functionality was originally implemented, the possibility
of 'clone --local' from within a worktree was overlooked, with the
result that the location of the "objects" directory of the source
repository was computed incorrectly, thus the objects could not be
copied or hard-linked by the clone. This shortcoming was addressed by
744e469 (clone: allow --local from a linked checkout, 2015-09-28).

However, the related case of 'clone --shared' (despite being handled
only a few lines away from the 'clone --local' case) was not fixed by
744e469, with a similar result of the "objects" directory location
being incorrectly computed for insertion into the 'alternates' file.
Fix this.

Reported-by: Marc-André Lureau <[email protected]>
Signed-off-by: Eric Sunshine <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: sunshineco

builtin/clone.c

@@ -423,7 +423,8 @@ static void clone_local(const char *src_repo, const char *dest_repo)
 {
 	if (option_shared) {
 		struct strbuf alt = STRBUF_INIT;
-		strbuf_addf(&alt, "%s/objects", src_repo);
+		get_common_dir(&alt, src_repo);
+		strbuf_addstr(&alt, "/objects");
 		add_to_alternates_file(alt.buf);
 		strbuf_release(&alt);
 	} else {

t/t2025-worktree-add.sh

@@ -198,4 +198,10 @@ test_expect_success 'local clone from linked checkout' '
 	( cd here-clone && git fsck )
 '
 
+test_expect_success 'local clone --shared from linked checkout' '
+	git -C bare worktree add --detach ../baretree &&
+	git clone --local --shared baretree bare-clone &&
+	grep /bare/ bare-clone/.git/objects/info/alternates
+'
+
 test_done