Merge branch 'ps/worktree-refdb-initialization'

Instead of manually creating refs/ hierarchy on disk upon a
creation of a secondary worktree, which is only usable via the
files backend, use the refs API to populate it.

* ps/worktree-refdb-initialization:
  builtin/worktree: create refdb via ref backend
  worktree: expose interface to look up worktree by name
  builtin/worktree: move setup of commondir file earlier
  refs/files: skip creation of "refs/{heads,tags}" for worktrees
  setup: move creation of "refs/" into the files backend
  refs: prepare `refs_init_db()` for initializing worktree refs

4 files changed, 37 insertions, 9 deletions

diff --git a/refs/debug.c b/refs/debug.c
index b9775f2c37..634681ca44 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -33,10 +33,10 @@ struct ref_store *maybe_debug_wrap_ref_store(const char *gitdir, struct ref_stor
 	return (struct ref_store *)res;
 }
 
-static int debug_init_db(struct ref_store *refs, struct strbuf *err)
+static int debug_init_db(struct ref_store *refs, int flags, struct strbuf *err)
 {
 	struct debug_ref_store *drefs = (struct debug_ref_store *)refs;
-	int res = drefs->refs->be->init_db(drefs->refs, err);
+	int res = drefs->refs->be->init_db(drefs->refs, flags, err);
 	trace_printf_key(&trace_refs, "init_db: %d\n", res);
 	return res;
 }
diff --git a/refs/files-backend.c b/refs/files-backend.c
index b288fc97db..75dcc21ecb 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3218,21 +3218,46 @@ static int files_reflog_expire(struct ref_store *ref_store,
 	return -1;
 }
 
-static int files_init_db(struct ref_store *ref_store, struct strbuf *err UNUSED)
+static int files_init_db(struct ref_store *ref_store,
+			 int flags,
+			 struct strbuf *err UNUSED)
 {
 	struct files_ref_store *refs =
 		files_downcast(ref_store, REF_STORE_WRITE, "init_db");
 	struct strbuf sb = STRBUF_INIT;
 
 	/*
-	 * Create .git/refs/{heads,tags}
+	 * We need to create a "refs" dir in any case so that older versions of
+	 * Git can tell that this is a repository. This serves two main purposes:
+	 *
+	 * - Clients will know to stop walking the parent-directory chain when
+	 *   detecting the Git repository. Otherwise they may end up detecting
+	 *   a Git repository in a parent directory instead.
+	 *
+	 * - Instead of failing to detect a repository with unknown reference
+	 *   format altogether, old clients will print an error saying that
+	 *   they do not understand the reference format extension.
 	 */
-	files_ref_path(refs, &sb, "refs/heads");
+	strbuf_addf(&sb, "%s/refs", ref_store->gitdir);
 	safe_create_dir(sb.buf, 1);
+	adjust_shared_perm(sb.buf);
 
-	strbuf_reset(&sb);
-	files_ref_path(refs, &sb, "refs/tags");
-	safe_create_dir(sb.buf, 1);
+	/*
+	 * There is no need to create directories for common refs when creating
+	 * a worktree ref store.
+	 */
+	if (!(flags & REFS_INIT_DB_IS_WORKTREE)) {
+		/*
+		 * Create .git/refs/{heads,tags}
+		 */
+		strbuf_reset(&sb);
+		files_ref_path(refs, &sb, "refs/heads");
+		safe_create_dir(sb.buf, 1);
+
+		strbuf_reset(&sb);
+		files_ref_path(refs, &sb, "refs/tags");
+		safe_create_dir(sb.buf, 1);
+	}
 
 	strbuf_release(&sb);
 	return 0;
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index bf04b93381..a499a91c7e 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1245,6 +1245,7 @@ static const char PACKED_REFS_HEADER[] =
 	"# pack-refs with: peeled fully-peeled sorted \n";
 
 static int packed_init_db(struct ref_store *ref_store UNUSED,
+			  int flags UNUSED,
 			  struct strbuf *err UNUSED)
 {
 	/* Nothing to do. */
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 8e9f04cc67..82219829b0 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -529,7 +529,9 @@ typedef struct ref_store *ref_store_init_fn(struct repository *repo,
 					    const char *gitdir,
 					    unsigned int flags);
 
-typedef int ref_init_db_fn(struct ref_store *refs, struct strbuf *err);
+typedef int ref_init_db_fn(struct ref_store *refs,
+			   int flags,
+			   struct strbuf *err);
 
 typedef int ref_transaction_prepare_fn(struct ref_store *refs,
 				       struct ref_transaction *transaction,