Re: [PATCH] setup: do not create $X/gitdir unnecessarily when accessing git file $X

$X/gitdir is created, or refreshed, in order to keep a linked worktree
from being pruned. But while git file is used as the foundation for
linked worktrees, it's used for other purposes as well and we should
not create $X/gitdir in those cases.

Tighten the check. Only update an existing file, which is an
indication this is a linked worktree.

Signed-off-by: Nguyễn Thái Ngọc Duy <redacted>
---

diff --git a/t/t0002-gitfile.sh b/t/t0002-gitfile.sh

@@ -99,6 +99,13 @@ test_expect_success 'check rev-list' '
+test_expect_success '$REAL/gitdir is not created on ordinary git file' '
+       echo "gitdir: $REAL" >expected &&
+       test_cmp expected .git &&
+       git status &&
+       ! test -f "$REAL"/gitdir