Re: [PATCH v3 2/4] refs: introduce get_worktree_ref_store()

files-backend at this point is still aware of the per-repo/worktree
separation in refs, so it can handle a linked worktree.

Some refs operations are known not working when current files-backend is
used in a linked worktree (e.g. reflog). Tests will be written when
refs_* functions start to be called with worktree backend to verify that
they work as expected.

Note: accessing a worktree of a submodule remains unaddressed. Perhaps
after get_worktrees() can access submodule (or rather a new function
get_submodule_worktrees(), that lists worktrees of a submodule), we can
update this function to work with submodules as well.
---
 refs.c | 32 ++++++++++++++++++++++++++++++++
 refs.h |  2 ++
 2 files changed, 34 insertions(+)

diff --git a/refs.c b/refs.c
index 77a39f8b17..6695140cfe 100644
--- a/refs.c
+++ b/refs.c

@@ -10,6 +10,7 @@
 #include "object.h"
 #include "tag.h"
 #include "submodule.h"
+#include "worktree.h"
 
 /*
  * List of all available backends

@@ -1593,6 +1594,37 @@ struct ref_store *get_submodule_ref_store(const char *submodule)
 	return refs;
 }
 
+struct ref_store *get_worktree_ref_store(const struct worktree *wt)
+{
+	struct ref_store *refs;
+	unsigned int refs_all_capabilities =
+		REF_STORE_READ | REF_STORE_WRITE |
+		REF_STORE_ODB | REF_STORE_MAIN;
+
+	if (wt->is_current)
+		return get_main_ref_store();
+
+	/*
+	 * We share the same hash map with submodules for
+	 * now. submodule paths are always relative (to topdir) while
+	 * worktree paths are always absolute. No chance of conflict.
+	 */
+	refs = lookup_submodule_ref_store(wt->path);
+	if (refs)
+		return refs;
+
+	if (wt->id)
+		refs = ref_store_init(git_common_path("worktrees/%s", wt->id),
+				      refs_all_capabilities);
+	else
+		refs = ref_store_init(get_git_common_dir(),
+				      refs_all_capabilities);
+
+	if (refs)
+		register_submodule_ref_store(refs, wt->path);
+	return refs;
+}
+