Add a place for (not) sharing stuff between worktrees

When multiple worktrees are used, we need rules to determine if
something belongs to one worktree or all of them. Instead of keeping
adding rules when new stuff comes (*), have a generic rule:

- Inside $GIT_DIR, which is per-worktree by default, add
  $GIT_DIR/common which is always shared. New features that want to
  share stuff should put stuff under this directory.

- Inside refs/, which is shared by default except refs/bisect, add
  refs/worktree/ which is per-worktree. We may eventually move
  refs/bisect to this new location and remove the exception in refs
  code.

(*) And it may also include stuff from external commands which will
    have no way to modify common/per-worktree rules.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 16ef9325e0..2dd77f9485 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -269,9 +269,9 @@ static void loose_fill_ref_dir(struct ref_store *ref_store,
 	closedir(d);
 
 	/*
-	 * Manually add refs/bisect, which, being per-worktree, might
-	 * not appear in the directory listing for refs/ in the main
-	 * repo.
+	 * Manually add refs/bisect and refs/worktree, which, being
+	 * per-worktree, might not appear in the directory listing for
+	 * refs/ in the main repo.
 	 */
 	if (!strcmp(dirname, "refs/")) {
 		int pos = search_ref_dir(dir, "refs/bisect/", 12);
@@ -281,6 +281,14 @@ static void loose_fill_ref_dir(struct ref_store *ref_store,
 					dir->cache, "refs/bisect/", 12, 1);
 			add_entry_to_dir(dir, child_entry);
 		}
+
+		pos = search_ref_dir(dir, "refs/worktree/", 11);
+
+		if (pos < 0) {
+			struct ref_entry *child_entry = create_dir_entry(
+					dir->cache, "refs/worktree/", 11, 1);
+			add_entry_to_dir(dir, child_entry);
+		}
 	}
 }