[PATCH] fsck: ignore missing "refs" directory for linked worktrees

[shejialuo <shejialuo@gmail.com>]

It is reported that "git refs verify" would fail when encountering
worktrees created on Git v2.43.0 or older versions. These versions
don't automatically create the "refs" directory, causing the error:

    error: cannot open directory .git/worktrees/<worktree name>/refs:
    No such file or directory

Since 8f4c00de95 (builtin/worktree: create refdb via ref backend,
2024-01-08), we automatically create the "refs" directory for new
worktrees. However, the fsck code incorrectly assumes all linked
worktrees have this directory, thus introducing compatibility issue.

Check for ENOENT errno before reporting directory access errors for
linked worktrees to maintain backward compatibility.

Reported-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: shejialuo <shejialuo@gmail.com>
---
 refs/files-backend.c     |  3 +++
 t/t0602-reffiles-fsck.sh | 15 +++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 4d1f65a57a..bf6f89b1d1 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3762,6 +3762,9 @@ static int files_fsck_refs_dir(struct ref_store *ref_store,
 
 	iter = dir_iterator_begin(sb.buf, 0);
 	if (!iter) {
+		if (errno == ENOENT && !is_main_worktree(wt))
+			goto out;
+
 		ret = error_errno(_("cannot open directory %s"), sb.buf);
 		goto out;
 	}
diff --git a/t/t0602-reffiles-fsck.sh b/t/t0602-reffiles-fsck.sh
index f671ac4d3a..615b7c0683 100755
--- a/t/t0602-reffiles-fsck.sh
+++ b/t/t0602-reffiles-fsck.sh
@@ -110,6 +110,21 @@ test_expect_success 'ref name check should be adapted into fsck messages' '
 	)
 '
 
+test_expect_success 'no refs directory of worktree should not cause problems' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit initial &&
+
+		git worktree add --detach ./worktree &&
+		# Simulate old directory layout
+		rm -rf ./git/worktrees/worktree/refs &&
+		git refs verify 2>err &&
+		test_must_be_empty err
+	)
+'
+
 test_expect_success 'ref name check should work for multiple worktrees' '
 	test_when_finished "rm -rf repo" &&
 	git init repo &&
-- 
2.49.0