Re: [PATCH 05/38] refs: create a base class "ref_store" for files_ref_store

We want ref_stores to be polymorphic, so invent a base class of which
files_ref_store is a derived class. For now there is a one-to-one
relationship between ref_stores and submodules.

Signed-off-by: Michael Haggerty <redacted>
---

diff --git a/refs/files-backend.c b/refs/files-backend.c

@@ -973,53 +967,54 @@ static void clear_loose_ref_cache(struct files_ref_store *refs)
+/*
+ * Downcast ref_store to files_ref_store. Die if ref_store is not a
+ * files_ref_store. If submodule_allowed is not true, then also die if
+ * files_ref_store is for a submodule (i.e., not for the main
+ * repository). caller is used in any necessary error messages.
+ */
+static struct files_ref_store *files_downcast(
+               struct ref_store *ref_store, int submodule_allowed,
+               const char *caller)
 {
        struct files_ref_store *refs;

+       if (ref_store->be != &refs_be_files)
+               die("BUG: ref_store is type \"%s\" not \"files\" in %s",
+                   ref_store->be->name, caller);

+       refs = (struct files_ref_store *)ref_store;
+
+       if (!submodule_allowed)
+               assert_main_repository(ref_store, caller);
+
+       return refs;
 }

diff --git a/refs/refs-internal.h b/refs/refs-internal.h

@@ -521,11 +521,89 @@ int read_raw_ref(const char *refname, unsigned char *sha1,
+/*
+ * A representation of the reference store for the main repository or
+ * a submodule. The ref_store instances for submodules are kept in a
+ * linked list.
+ */
+struct ref_store {
+       /* The backend describing this ref_store's storage scheme: */
+       const struct ref_storage_be *be;
+
+       /*
+        * The name of the submodule represented by this object, or
+        * the empty string if it represents the main repository's
+        * reference store:
+        */
+       const char *submodule;