Merge branch 'hn/refs-fetch-head-is-special'

The FETCH_HEAD is now always read from the filesystem regardless of
the ref backend in use, as its format is much richer than the
normal refs, and written directly by "git fetch" as a plain file..

* hn/refs-fetch-head-is-special:
  refs: read FETCH_HEAD and MERGE_HEAD generically
  refs: move gitdir into base ref_store
  refs: fix comment about submodule ref_stores
  refs: split off reading loose ref data in separate function

refs.c

@@ -1527,11 +1527,37 @@ int for_each_rawref(each_ref_fn fn, void *cb_data)
 	return refs_for_each_rawref(get_main_ref_store(the_repository), fn, cb_data);
 }
 
+static int refs_read_special_head(struct ref_store *ref_store,
+				  const char *refname, struct object_id *oid,
+				  struct strbuf *referent, unsigned int *type)
+{
+	struct strbuf full_path = STRBUF_INIT;
+	struct strbuf content = STRBUF_INIT;
+	int result = -1;
+	strbuf_addf(&full_path, "%s/%s", ref_store->gitdir, refname);
+
+	if (strbuf_read_file(&content, full_path.buf, 0) < 0)
+		goto done;
+
+	result = parse_loose_ref_contents(content.buf, oid, referent, type);
+
+done:
+	strbuf_release(&full_path);
+	strbuf_release(&content);
+	return result;
+}
+
 int refs_read_raw_ref(struct ref_store *ref_store,
 		      const char *refname, struct object_id *oid,
 		      struct strbuf *referent, unsigned int *type)
 {
-	return ref_store->be->read_raw_ref(ref_store, refname, oid, referent, type);
+	if (!strcmp(refname, "FETCH_HEAD") || !strcmp(refname, "MERGE_HEAD")) {
+		return refs_read_special_head(ref_store, refname, oid, referent,
+					      type);
+	}
+
+	return ref_store->be->read_raw_ref(ref_store, refname, oid, referent,
+					   type);
 }
 
 /* This function needs to return a meaningful errno on failure */