This does not matter as long as the Git executable is doing the asking,
as the path for that `index.lock` file is constructed from
`git_path("index")` by appending the `.lock` suffix.

However, Git GUI just learned to use `--git-path` instead of appending
relative paths to what `git rev-parse --git-dir` returns (and as a
consequence not only using the correct hooks directory, but also using
the correct paths in worktrees other than the main one). And one of the
paths it is looking for is... you guessed it... `index.lock`.

So let's make that work as script writers would expect it to.

Signed-off-by: Johannes Schindelin <redacted>
---
 path.c               |  4 ++--
 t/t1500-rev-parse.sh | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/path.c b/path.c
index e3da1f3c4e..ff85692b45 100644
--- a/path.c
+++ b/path.c

@@ -268,7 +268,7 @@ static int trie_find(struct trie *root, const char *key, match_fn fn,
 	int result;
 	struct trie *child;
 
-	if (!*key) {
+	if (!*key || !strcmp(key, ".lock")) {
 		/* we have reached the end of the key */
 		if (root->value && !root->len)
 			return fn(key, root->value, baton);

@@ -288,7 +288,7 @@ static int trie_find(struct trie *root, const char *key, match_fn fn,
 
 	/* Matched the entire compressed section */
 	key += i;
-	if (!*key)
+	if (!*key || !strcmp(key, ".lock"))
 		/* End of key */
 		return fn(key, root->value, baton);
 

diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
index 01abee533d..d318a1eeef 100755
--- a/t/t1500-rev-parse.sh
+++ b/t/t1500-rev-parse.sh

@@ -116,6 +116,21 @@ test_expect_success 'git-path inside sub-dir' '
 	test_cmp expect actual
 '
 
+test_expect_success 'git-path in worktree' '
+	test_tick &&
+	git commit --allow-empty -m empty &&
+	git worktree add --detach wt &&
+	test_write_lines >expect \
+		"$(pwd)/.git/worktrees/wt/logs/HEAD" \
+		"$(pwd)/.git/worktrees/wt/logs/HEAD.lock" \
+		"$(pwd)/.git/worktrees/wt/index" \
+		"$(pwd)/.git/worktrees/wt/index.lock" &&
+	git -C wt rev-parse >actual \
+		--git-path logs/HEAD --git-path logs/HEAD.lock \
+		--git-path index --git-path index.lock &&
+	test_cmp expect actual