refs: check submodules' ref storage config

All submodules must have the same ref storage (for now).  Confirm that
this is so before attempting to do anything with submodule refs.

Signed-off-by: David Turner <dturner@twopensource.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 57 insertions, 7 deletions

diff --git a/refs.c b/refs.c
index f132792e2d..24be63c4e6 100644
--- a/refs.c
+++ b/refs.c
@@ -302,6 +302,54 @@ int for_each_tag_ref(each_ref_fn fn, void *cb_data)
 	return for_each_ref_in("refs/tags/", fn, cb_data);
 }
 
+static int submodule_backend(const char *key, const char *value, void *data)
+{
+	const char **path = data;
+	char **old_path = data;
+	if (!strcmp(key, "extensions.refstorage") &&
+	    !git_config_string(path, key, "extensions.refstorage"))
+			free(*old_path);
+
+	return 0;
+}
+
+/*
+ * Check that a submodule exists. If its ref storage backend differs
+ * from the current backend, die.  If the submodule exists, return
+ * 0. Else return -1.
+ */
+static int check_submodule_backend(const char *submodule)
+{
+	struct strbuf sb = STRBUF_INIT;
+	char *submodule_storage_backend;
+	int result = -1;
+
+	if (!submodule)
+		return 0;
+
+	submodule_storage_backend = xstrdup("files");
+
+	strbuf_addstr(&sb, submodule);
+	if (!is_nonbare_repository_dir(&sb))
+		goto done;
+
+	strbuf_reset(&sb);
+	strbuf_git_path_submodule(&sb, submodule, "config");
+
+	git_config_from_file(submodule_backend, sb.buf,
+			     &submodule_storage_backend);
+	if (strcmp(submodule_storage_backend, ref_storage_backend))
+		die(_("Ref storage '%s' for submodule '%s' does not match our storage, '%s'"),
+		    submodule_storage_backend, submodule, ref_storage_backend);
+
+	result = 0;
+done:
+	free(submodule_storage_backend);
+	strbuf_release(&sb);
+
+	return result;
+}
+
 int for_each_tag_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
 {
 	return for_each_ref_in_submodule(submodule, "refs/tags/", fn, cb_data);
@@ -314,6 +362,7 @@ int for_each_branch_ref(each_ref_fn fn, void *cb_data)
 
 int for_each_branch_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
 {
+	check_submodule_backend(submodule);
 	return for_each_ref_in_submodule(submodule, "refs/heads/", fn, cb_data);
 }
 
@@ -324,6 +373,7 @@ int for_each_remote_ref(each_ref_fn fn, void *cb_data)
 
 int for_each_remote_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
 {
+	check_submodule_backend(submodule);
 	return for_each_ref_in_submodule(submodule, "refs/remotes/", fn, cb_data);
 }
 
@@ -1135,6 +1185,7 @@ int head_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
 	int flag;
 
 	if (submodule) {
+		check_submodule_backend(submodule);
 		if (resolve_gitlink_ref(submodule, "HEAD", oid.hash) == 0)
 			return fn("HEAD", &oid, 0, cb_data);
 
@@ -1558,6 +1609,9 @@ int create_symref(const char *ref_target, const char *refs_heads_master,
 int resolve_gitlink_ref(const char *path, const char *refname,
 			unsigned char *sha1)
 {
+	if (check_submodule_backend(path))
+		return -1;
+
 	return the_refs_backend->resolve_gitlink_ref(path, refname, sha1);
 }
 
diff --git a/refs.h b/refs.h
index f08e886803..456e7296dc 100644
--- a/refs.h
+++ b/refs.h
@@ -511,7 +511,7 @@ extern int reflog_expire(const char *refname, const unsigned char *sha1,
 			 void *policy_cb_data);
 
 /*
- * Read the refdb storage backend name out of the config file
+ * Read the ref storage backend name out of the config file
  */
 int ref_storage_backend_config(const char *var, const char *value, void *ptr);
 
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 5821adb9bb..707f1ec9c1 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -1355,13 +1355,9 @@ static int files_resolve_gitlink_ref(const char *path, const char *refname,
 
 	strbuf_add(&submodule, path, len);
 	refs = lookup_ref_cache(submodule.buf);
-	if (!refs) {
-		if (!is_nonbare_repository_dir(&submodule)) {
-			strbuf_release(&submodule);
-			return -1;
-		}
+	if (!refs)
 		refs = create_ref_cache(submodule.buf);
-	}
+
 	strbuf_release(&submodule);
 
 	retval = resolve_gitlink_ref_recursive(refs, refname, sha1, 0);