Merge branch 'nd/per-worktree-ref-iteration'

The code to traverse objects for reachability, used to decide what
objects are unreferenced and expendable, have been taught to also
consider per-worktree refs of other worktrees as starting points to
prevent data loss.

* nd/per-worktree-ref-iteration:
  git-worktree.txt: correct linkgit command name
  reflog expire: cover reflog from all worktrees
  fsck: check HEAD and reflog from other worktrees
  fsck: move fsck_head_link() to get_default_heads() to avoid some globals
  revision.c: better error reporting on ref from different worktrees
  revision.c: correct a parameter name
  refs: new ref types to make per-worktree refs visible to all worktrees
  Add a place for (not) sharing stuff between worktrees
  refs.c: indent with tabs, not spaces

worktree.h

@@ -108,4 +108,28 @@ extern const char *worktree_git_path(const struct worktree *wt,
 				     const char *fmt, ...)
 	__attribute__((format (printf, 2, 3)));
 
+/*
+ * Parse a worktree ref (i.e. with prefix main-worktree/ or
+ * worktrees/) and return the position of the worktree's name and
+ * length (or NULL and zero if it's main worktree), and ref.
+ *
+ * All name, name_length and ref arguments could be NULL.
+ */
+int parse_worktree_ref(const char *worktree_ref, const char **name,
+		       int *name_length, const char **ref);
+
+/*
+ * Return a refname suitable for access from the current ref store.
+ */
+void strbuf_worktree_ref(const struct worktree *wt,
+			 struct strbuf *sb,
+			 const char *refname);
+
+/*
+ * Return a refname suitable for access from the current ref
+ * store. The result will be destroyed at the next call.
+ */
+const char *worktree_ref(const struct worktree *wt,
+			 const char *refname);
+
 #endif