odb: move logic to disable ref updates into repo

Our object database sources have a field `disable_ref_updates`. This
field can obviously be set to disable reference updates, but it is
somewhat curious that this logic is hosted by the object database.

The reason for this is that it was primarily added to keep us from
accidentally updating references while an ODB transaction is ongoing.
Any objects part of the transaction have not yet been committed to disk,
so new references that point to them might get corrupted in case we
never end up committing the transaction. As such, whenever we create a
new transaction we set up a new temporary ODB source and mark it as
disabling reference updates.

This has one (and only one?) upside: once we have committed the
transaction, the temporary source will be dropped and thus we clean up
the disabled reference updates automatically. But other than that, it's
somewhat misdesigned:

  - We can have multiple ODB sources, but only the currently active
    source inhibits reference updates.

  - We're mixing concerns of the refdb with the ODB.

Arguably, the decision of whether we can update references or not should
be handled by the refdb. But that wouldn't be a great fit either, as
there can be one refdb per worktree. So we'd again have the same problem
that a "global" intent becomes localized to a specific instance.

Instead, move the setting into the repository. While at it, convert it
into a boolean.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

odb.c

@@ -360,7 +360,7 @@ struct odb_source *odb_set_temporary_primary_source(struct object_database *odb,
 	 * Disable ref updates while a temporary odb is active, since
 	 * the objects in the database may roll back.
 	 */
-	source->disable_ref_updates = 1;
+	odb->repo->disable_ref_updates = true;
 	source->will_destroy = will_destroy;
 	source->next = odb->sources;
 	odb->sources = source;
@@ -387,6 +387,7 @@ void odb_restore_primary_source(struct object_database *odb,
 	if (cur_source->next != restore_source)
 		BUG("we expect the old primary object store to be the first alternate");
 
+	odb->repo->disable_ref_updates = false;
 	odb->sources = restore_source;
 	odb_source_free(cur_source);
 }

odb.h

@@ -66,13 +66,6 @@ struct odb_source {
 	 */
 	bool local;
 
-	/*
-	 * This is a temporary object store created by the tmp_objdir
-	 * facility. Disable ref updates since the objects in the store
-	 * might be discarded on rollback.
-	 */
-	int disable_ref_updates;
-
 	/*
 	 * This object store is ephemeral, so there is no need to fsync.
 	 */

refs.c

@@ -2491,7 +2491,7 @@ int ref_transaction_prepare(struct ref_transaction *transaction,
 		break;
 	}
 
-	if (refs->repo->objects->sources->disable_ref_updates) {
+	if (refs->repo->disable_ref_updates) {
 		strbuf_addstr(err,
 			      _("ref updates forbidden inside quarantine environment"));
 		return -1;

repository.c

@@ -179,7 +179,7 @@ void repo_set_gitdir(struct repository *repo,
 		repo->objects->sources->path = objects_path;
 	}
 
-	repo->objects->sources->disable_ref_updates = o->disable_ref_updates;
+	repo->disable_ref_updates = o->disable_ref_updates;
 
 	free(repo->objects->alternate_db);
 	repo->objects->alternate_db = xstrdup_or_null(o->alternate_db);

repository.h

@@ -71,6 +71,13 @@ struct repository {
 	 */
 	struct ref_store *refs_private;
 
+	/*
+	 * Disable ref updates. This is especially used in contexts where
+	 * transactions may still be rolled back so that we don't start to
+	 * reference objects that may vanish.
+	 */
+	bool disable_ref_updates;
+
 	/*
 	 * A strmap of ref_stores, stored by submodule name, accessible via
 	 * `repo_get_submodule_ref_store()`.
@@ -187,7 +194,7 @@ struct set_gitdir_args {
 	const char *graft_file;
 	const char *index_file;
 	const char *alternate_db;
-	int disable_ref_updates;
+	bool disable_ref_updates;
 };
 
 void repo_set_gitdir(struct repository *repo, const char *root,

setup.c

@@ -1682,7 +1682,7 @@ void setup_git_env(const char *git_dir)
 	args.index_file = getenv_safe(&to_free, INDEX_ENVIRONMENT);
 	args.alternate_db = getenv_safe(&to_free, ALTERNATE_DB_ENVIRONMENT);
 	if (getenv(GIT_QUARANTINE_ENVIRONMENT)) {
-		args.disable_ref_updates = 1;
+		args.disable_ref_updates = true;
 	}
 
 	repo_set_gitdir(the_repository, git_dir, &args);