files-backend: replace submodule_allowed check in files_downcast()

files-backend.c is unlearning submodules. Instead of having a specific
check for submodules to see what operation is allowed, files backend
now takes a set of flags at init. Each operation will check if the
required flags is present before performing.

For now we have four flags: read, write and odb access. Main ref store
has all flags, obviously, while submodule stores are read-only and have
access to odb (*).

The "main" flag stays because many functions in the backend calls
frontend ones without a ref store, so these functions always target the
main ref store. Ideally the flag should be gone after ref-store-aware
api is in place and used by backends.

(*) Submodule code needs for_each_ref. Try take REF_STORE_ODB flag
out. At least t3404 would fail. The "have access to odb" in submodule is
a bit hacky since we don't know from he whether add_submodule_odb() has
been called.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/refs.c b/refs.c
index d72b48a430..c7bffac06d 100644
--- a/refs.c
+++ b/refs.c
@@ -1416,7 +1416,8 @@ static struct ref_store *lookup_submodule_ref_store(const char *submodule)
  * Create, record, and return a ref_store instance for the specified
  * gitdir.
  */
-static struct ref_store *ref_store_init(const char *gitdir)
+static struct ref_store *ref_store_init(const char *gitdir,
+					unsigned int flags)
 {
 	const char *be_name = "files";
 	struct ref_storage_be *be = find_ref_storage_backend(be_name);
@@ -1425,7 +1426,7 @@ static struct ref_store *ref_store_init(const char *gitdir)
 	if (!be)
 		die("BUG: reference backend %s is unknown", be_name);
 
-	refs = be->init(gitdir);
+	refs = be->init(gitdir, flags);
 	return refs;
 }
 
@@ -1434,7 +1435,11 @@ struct ref_store *get_main_ref_store(void)
 	if (main_ref_store)
 		return main_ref_store;
 
-	main_ref_store = ref_store_init(get_git_dir());
+	main_ref_store = ref_store_init(get_git_dir(),
+					(REF_STORE_READ |
+					 REF_STORE_WRITE |
+					 REF_STORE_ODB |
+					 REF_STORE_MAIN));
 	return main_ref_store;
 }
 
@@ -1481,7 +1486,9 @@ struct ref_store *get_ref_store(const char *submodule)
 		return NULL;
 	}
 
-	refs = ref_store_init(submodule_sb.buf);
+	/* assume that add_submodule_odb() has been called */
+	refs = ref_store_init(submodule_sb.buf,
+			      REF_STORE_READ | REF_STORE_ODB);
 	register_submodule_ref_store(refs, submodule);
 
 	strbuf_release(&submodule_sb);