refs: remove the_hash_algo global state

refs.c uses the_hash_algo in multiple places, relying on global state for
the object hash algorithm. Replace these uses with the appropriate
repository-specific hash_algo. In transaction-related functions
(ref_transaction_create, ref_transaction_delete, migrate_one_ref, and
transaction_hook_feed_stdin), use transaction->ref_store->repo->hash_algo.
In other cases, such as repo_get_submodule_ref_store(), use
repo->hash_algo.

Signed-off-by: Shreyansh Paliwal <shreyanshpaliwalcmsmn@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: shreyp135

refs.c

@@ -1472,7 +1472,7 @@ int ref_transaction_create(struct ref_transaction *transaction,
 		return 1;
 	}
 	return ref_transaction_update(transaction, refname, new_oid,
-				      null_oid(the_hash_algo), new_target, NULL, flags,
+				      null_oid(transaction->ref_store->repo->hash_algo), new_target, NULL, flags,
 				      msg, err);
 }
 
@@ -1491,7 +1491,7 @@ int ref_transaction_delete(struct ref_transaction *transaction,
 	if (old_target && !(flags & REF_NO_DEREF))
 		BUG("delete cannot operate on symrefs with deref mode");
 	return ref_transaction_update(transaction, refname,
-				      null_oid(the_hash_algo), old_oid,
+				      null_oid(transaction->ref_store->repo->hash_algo), old_oid,
 				      NULL, old_target, flags,
 				      msg, err);
 }
@@ -2379,7 +2379,7 @@ struct ref_store *repo_get_submodule_ref_store(struct repository *repo,
 	subrepo = xmalloc(sizeof(*subrepo));
 
 	if (repo_submodule_init(subrepo, repo, submodule,
-				null_oid(the_hash_algo))) {
+				null_oid(repo->hash_algo))) {
 		free(subrepo);
 		goto done;
 	}
@@ -2571,14 +2571,14 @@ static int transaction_hook_feed_stdin(int hook_stdin_fd, void *pp_cb, void *pp_
 	strbuf_reset(buf);
 
 	if (!(update->flags & REF_HAVE_OLD))
-		strbuf_addf(buf, "%s ", oid_to_hex(null_oid(the_hash_algo)));
+		strbuf_addf(buf, "%s ", oid_to_hex(null_oid(transaction->ref_store->repo->hash_algo)));
 	else if (update->old_target)
 		strbuf_addf(buf, "ref:%s ", update->old_target);
 	else
 		strbuf_addf(buf, "%s ", oid_to_hex(&update->old_oid));
 
 	if (!(update->flags & REF_HAVE_NEW))
-		strbuf_addf(buf, "%s ", oid_to_hex(null_oid(the_hash_algo)));
+		strbuf_addf(buf, "%s ", oid_to_hex(null_oid(transaction->ref_store->repo->hash_algo)));
 	else if (update->new_target)
 		strbuf_addf(buf, "ref:%s ", update->new_target);
 	else
@@ -3145,6 +3145,7 @@ struct migration_data {
 static int migrate_one_ref(const struct reference *ref, void *cb_data)
 {
 	struct migration_data *data = cb_data;
+	const struct git_hash_algo *hash_algo = data->transaction->ref_store->repo->hash_algo;
 	struct strbuf symref_target = STRBUF_INIT;
 	int ret;
 
@@ -3153,7 +3154,7 @@ static int migrate_one_ref(const struct reference *ref, void *cb_data)
 		if (ret < 0)
 			goto done;
 
-		ret = ref_transaction_update(data->transaction, ref->name, NULL, null_oid(the_hash_algo),
+		ret = ref_transaction_update(data->transaction, ref->name, NULL, null_oid(hash_algo),
 					     symref_target.buf, NULL,
 					     REF_SKIP_CREATE_REFLOG | REF_NO_DEREF, NULL, data->errbuf);
 		if (ret < 0)