[RFC PATCH 3/3] fsck: Check HEAD of other worktrees as well

[Elijah Newren <newren@gmail.com>]

This takes advantage of the fact that "worktrees/$WORKTREE/HEAD" will
currently resolve as a ref, which may not be true in the future with
different ref backends.  I don't think it locks us in to supporting
resolving other worktree HEADs with this syntax, as I view the
user-visible error message as more of a pointer to a pathname that the
user will need to fix.  If the underlying ref storage changes, naturally
both this code and the hint may need to change to match.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 builtin/fsck.c  | 60 +++++++++++++++++++++++++++++++++++++++++++++------------
 t/t1450-fsck.sh |  6 +++---
 2 files changed, 51 insertions(+), 15 deletions(-)

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 4132034170..850b217e93 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -451,17 +451,51 @@ static int fsck_handle_ref(const char *refname, const struct object_id *oid,
 	return 0;
 }
 
-static int fsck_head_link(const char **head_points_at,
+static void get_worktree_names(struct string_list *names)
+{
+	struct strbuf path = STRBUF_INIT;
+	DIR *dir;
+	struct dirent *d;
+
+	strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
+	dir = opendir(path.buf);
+	strbuf_release(&path);
+	if (dir) {
+		while ((d = readdir(dir)) != NULL) {
+			if (!is_dot_or_dotdot(d->d_name))
+				string_list_append(names, d->d_name);
+		}
+		closedir(dir);
+	}
+}
+
+static int fsck_head_link(const char *head_ref_name,
+			  const char **head_points_at,
 			  struct object_id *head_oid);
 
 static void get_default_heads(void)
 {
 	const char *head_points_at;
 	struct object_id head_oid;
+	struct string_list worktree_names = STRING_LIST_INIT_DUP;
+	struct string_list_item *worktree_item;
+	struct strbuf head_name = STRBUF_INIT;
 
-	fsck_head_link(&head_points_at, &head_oid);
+	fsck_head_link("HEAD", &head_points_at, &head_oid);
 	if (head_points_at && !is_null_oid(&head_oid))
 		fsck_handle_ref("HEAD", &head_oid, 0, NULL);
+
+	get_worktree_names(&worktree_names);
+	for_each_string_list_item(worktree_item, &worktree_names) {
+		strbuf_reset(&head_name);
+		strbuf_addf(&head_name, "worktrees/%s/HEAD",
+			    worktree_item->string);
+		fsck_head_link(head_name.buf, &head_points_at, &head_oid);
+		if (head_points_at && !is_null_oid(&head_oid))
+			fsck_handle_ref(head_name.buf, &head_oid, 0, NULL);
+	}
+	strbuf_release(&head_name);
+
 	for_each_rawref(fsck_handle_ref, NULL);
 	if (include_reflogs)
 		for_each_reflog(fsck_handle_reflog, NULL);
@@ -553,34 +587,36 @@ static void fsck_object_dir(const char *path)
 	stop_progress(&progress);
 }
 
-static int fsck_head_link(const char **head_points_at,
+static int fsck_head_link(const char *head_ref_name,
+			  const char **head_points_at,
 			  struct object_id *head_oid)
 {
 	int null_is_error = 0;
 
 	if (verbose)
-		fprintf(stderr, "Checking HEAD link\n");
+		fprintf(stderr, "Checking %s link\n", head_ref_name);
 
-	*head_points_at = resolve_ref_unsafe("HEAD", 0, head_oid, NULL);
+	*head_points_at = resolve_ref_unsafe(head_ref_name, 0, head_oid, NULL);
 	if (!*head_points_at) {
 		errors_found |= ERROR_REFS;
-		return error("Invalid HEAD");
+		return error("Invalid %s", head_ref_name);
 	}
-	if (!strcmp(*head_points_at, "HEAD"))
+	if (!strcmp(*head_points_at, head_ref_name))
 		/* detached HEAD */
 		null_is_error = 1;
 	else if (!starts_with(*head_points_at, "refs/heads/")) {
 		errors_found |= ERROR_REFS;
-		return error("HEAD points to something strange (%s)",
-			     *head_points_at);
+		return error("%s points to something strange (%s)",
+			     head_ref_name, *head_points_at);
 	}
 	if (is_null_oid(head_oid)) {
 		if (null_is_error) {
 			errors_found |= ERROR_REFS;
-			return error("HEAD: detached HEAD points at nothing");
+			return error("%s: detached HEAD points at nothing",
+				     head_ref_name);
 		}
-		fprintf(stderr, "notice: HEAD points to an unborn branch (%s)\n",
-			*head_points_at + 11);
+		fprintf(stderr, "notice: %s points to an unborn branch (%s)\n",
+			head_ref_name, *head_points_at + 11);
 	}
 	return 0;
 }
diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index fa94c59458..3da651be4c 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -102,7 +102,7 @@ test_expect_success 'HEAD link pointing at a funny place' '
 	grep "HEAD points to something strange" out
 '
 
-test_expect_failure 'other worktree HEAD link pointing at a funny object' '
+test_expect_success 'other worktree HEAD link pointing at a funny object' '
 	test_when_finished "rm -rf .git/worktrees" &&
 	mkdir -p .git/worktrees/other &&
 	echo 0000000000000000000000000000000000000000 >.git/worktrees/other/HEAD &&
@@ -111,7 +111,7 @@ test_expect_failure 'other worktree HEAD link pointing at a funny object' '
 	grep "worktrees/other/HEAD: detached HEAD points" out
 '
 
-test_expect_failure 'other worktree HEAD link pointing at missing object' '
+test_expect_success 'other worktree HEAD link pointing at missing object' '
 	test_when_finished "rm -rf .git/worktrees" &&
 	mkdir -p .git/worktrees/other &&
 	echo "Contents missing from repo" | git hash-object --stdin >.git/worktrees/other/HEAD &&
@@ -120,7 +120,7 @@ test_expect_failure 'other worktree HEAD link pointing at missing object' '
 	grep "worktrees/other/HEAD: invalid sha1 pointer" out
 '
 
-test_expect_failure 'other worktree HEAD link pointing at a funny place' '
+test_expect_success 'other worktree HEAD link pointing at a funny place' '
 	test_when_finished "rm -rf .git/worktrees" &&
 	mkdir -p .git/worktrees/other &&
 	echo "ref: refs/funny/place" >.git/worktrees/other/HEAD &&
-- 
2.16.1.75.gc01c8fdd7d