refs: accept symref values in ref_transaction_update()

The function `ref_transaction_update()` obtains ref information and
flags to create a `ref_update` and add them to the transaction at hand.

To extend symref support in transactions, we need to also accept the
old and new ref targets and process it. This commit adds the required
parameters to the function and modifies all call sites.

The two parameters added are `new_target` and `old_target`. The
`new_target` is used to denote what the reference should point to when
the transaction is applied. Some functions allow this parameter to be
NULL, meaning that the reference is not changed.

The `old_target` denotes the value the reference must have before the
update. Some functions allow this parameter to be NULL, meaning that the
old value of the reference is not checked.

We also update the internal function `ref_transaction_add_update()`
similarly to take the two new parameters.

Signed-off-by: Karthik Nayak <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: KarthikNayak

branch.c

@@ -627,7 +627,7 @@ void create_branch(struct repository *r,
 	if (!transaction ||
 		ref_transaction_update(transaction, ref.buf,
 					&oid, forcing ? NULL : null_oid(),
-					0, msg, &err) ||
+					NULL, NULL, 0, msg, &err) ||
 		ref_transaction_commit(transaction, &err))
 		die("%s", err.buf);
 	ref_transaction_free(transaction);

builtin/fast-import.c

@@ -1634,7 +1634,7 @@ static int update_branch(struct branch *b)
 	transaction = ref_transaction_begin(&err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, b->name, &b->oid, &old_oid,
-				   0, msg, &err) ||
+				   NULL, NULL, 0, msg, &err) ||
 	    ref_transaction_commit(transaction, &err)) {
 		ref_transaction_free(transaction);
 		error("%s", err.buf);
@@ -1675,7 +1675,8 @@ static void dump_tags(void)
 		strbuf_addf(&ref_name, "refs/tags/%s", t->name);
 
 		if (ref_transaction_update(transaction, ref_name.buf,
-					   &t->oid, NULL, 0, msg, &err)) {
+					   &t->oid, NULL, NULL, NULL,
+					   0, msg, &err)) {
 			failure |= error("%s", err.buf);
 			goto cleanup;
 		}

builtin/fetch.c

@@ -667,7 +667,7 @@ static int s_update_ref(const char *action,
 
 	ret = ref_transaction_update(transaction, ref->name, &ref->new_oid,
 				     check_old ? &ref->old_oid : NULL,
-				     0, msg, &err);
+				     NULL, NULL, 0, msg, &err);
 	if (ret) {
 		ret = STORE_REF_ERROR_OTHER;
 		goto out;

builtin/receive-pack.c

@@ -1595,6 +1595,7 @@ static const char *update(struct command *cmd, struct shallow_info *si)
 		if (ref_transaction_update(transaction,
 					   namespaced_name,
 					   new_oid, old_oid,
+					   NULL, NULL,
 					   0, "push",
 					   &err)) {
 			rp_error("%s", err.buf);

builtin/replace.c

@@ -201,7 +201,7 @@ static int replace_object_oid(const char *object_ref,
 	transaction = ref_transaction_begin(&err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, ref.buf, repl, &prev,
-				   0, NULL, &err) ||
+				   NULL, NULL, 0, NULL, &err) ||
 	    ref_transaction_commit(transaction, &err))
 		res = error("%s", err.buf);
 

builtin/tag.c

@@ -660,6 +660,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 	transaction = ref_transaction_begin(&err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, ref.buf, &object, &prev,
+				   NULL, NULL,
 				   create_reflog ? REF_FORCE_CREATE_REFLOG : 0,
 				   reflog_msg.buf, &err) ||
 	    ref_transaction_commit(transaction, &err)) {

builtin/update-ref.c

@@ -204,6 +204,7 @@ static void parse_cmd_update(struct ref_transaction *transaction,
 
 	if (ref_transaction_update(transaction, refname,
 				   &new_oid, have_old ? &old_oid : NULL,
+				   NULL, NULL,
 				   update_flags | create_reflog_flag,
 				   msg, &err))
 		die("%s", err.buf);

refs.c

@@ -1228,13 +1228,19 @@ struct ref_update *ref_transaction_add_update(
 		const char *refname, unsigned int flags,
 		const struct object_id *new_oid,
 		const struct object_id *old_oid,
+		const char *new_target, const char *old_target,
 		const char *msg)
 {
 	struct ref_update *update;
 
 	if (transaction->state != REF_TRANSACTION_OPEN)
 		BUG("update called for transaction that is not open");
 
+	if (old_oid && old_target)
+		BUG("only one of old_oid and old_target should be non NULL");
+	if (new_oid && new_target)
+		BUG("only one of new_oid and new_target should be non NULL");
+
 	FLEX_ALLOC_STR(update, refname, refname);
 	ALLOC_GROW(transaction->updates, transaction->nr + 1, transaction->alloc);
 	transaction->updates[transaction->nr++] = update;
@@ -1253,6 +1259,8 @@ int ref_transaction_update(struct ref_transaction *transaction,
 			   const char *refname,
 			   const struct object_id *new_oid,
 			   const struct object_id *old_oid,
+			   const char *new_target,
+			   const char *old_target,
 			   unsigned int flags, const char *msg,
 			   struct strbuf *err)
 {
@@ -1280,7 +1288,8 @@ int ref_transaction_update(struct ref_transaction *transaction,
 	flags |= (new_oid ? REF_HAVE_NEW : 0) | (old_oid ? REF_HAVE_OLD : 0);
 
 	ref_transaction_add_update(transaction, refname, flags,
-				   new_oid, old_oid, msg);
+				   new_oid, old_oid, new_target,
+				   old_target, msg);
 	return 0;
 }
 
@@ -1295,7 +1304,8 @@ int ref_transaction_create(struct ref_transaction *transaction,
 		return 1;
 	}
 	return ref_transaction_update(transaction, refname, new_oid,
-				      null_oid(), flags, msg, err);
+				      null_oid(), NULL, NULL, flags,
+				      msg, err);
 }
 
 int ref_transaction_delete(struct ref_transaction *transaction,
@@ -1308,7 +1318,8 @@ int ref_transaction_delete(struct ref_transaction *transaction,
 		BUG("delete called with old_oid set to zeros");
 	return ref_transaction_update(transaction, refname,
 				      null_oid(), old_oid,
-				      flags, msg, err);
+				      NULL, NULL, flags,
+				      msg, err);
 }
 
 int ref_transaction_verify(struct ref_transaction *transaction,
@@ -1321,6 +1332,7 @@ int ref_transaction_verify(struct ref_transaction *transaction,
 		BUG("verify called with old_oid set to NULL");
 	return ref_transaction_update(transaction, refname,
 				      NULL, old_oid,
+				      NULL, NULL,
 				      flags, NULL, err);
 }
 
@@ -1335,8 +1347,8 @@ int refs_update_ref(struct ref_store *refs, const char *msg,
 
 	t = ref_store_transaction_begin(refs, &err);
 	if (!t ||
-	    ref_transaction_update(t, refname, new_oid, old_oid, flags, msg,
-				   &err) ||
+	    ref_transaction_update(t, refname, new_oid, old_oid, NULL, NULL,
+				   flags, msg, &err) ||
 	    ref_transaction_commit(t, &err)) {
 		ret = 1;
 		ref_transaction_free(t);

refs.h

@@ -648,6 +648,16 @@ struct ref_transaction *ref_transaction_begin(struct strbuf *err);
  *         before the update. A copy of this value is made in the
  *         transaction.
  *
+ *     new_target -- the target reference that the reference will be
+ *         updated to point to. If the reference is a regular reference,
+ *         it will be converted to a symbolic reference. Cannot be set
+ *         together with `new_oid`. A copy of this value is made in the
+ *         transaction.
+ *
+ *     old_target -- the reference that the reference must be pointing to.
+ *         Canont be set together with `old_oid`. A copy of this value is
+ *         made in the transaction.
+ *
  *     flags -- flags affecting the update, passed to
  *         update_ref_lock(). Possible flags: REF_NO_DEREF,
  *         REF_FORCE_CREATE_REFLOG. See those constants for more
@@ -713,7 +723,11 @@ struct ref_transaction *ref_transaction_begin(struct strbuf *err);
  * beforehand. The old value is checked after the lock is taken to
  * prevent races. If the old value doesn't agree with old_oid, the
  * whole transaction fails. If old_oid is NULL, then the previous
- * value is not checked.
+ * value is not checked. If `old_target` is not NULL, treat the reference
+ * as a symbolic ref and validate that its target before the update is
+ * `old_target`. If the `new_target` is not NULL, then the reference
+ * will be updated to a symbolic ref which targets `new_target`.
+ * Together, these allow us to update between regular refs and symrefs.
  *
  * See the above comment "Reference transaction updates" for more
  * information.
@@ -722,6 +736,8 @@ int ref_transaction_update(struct ref_transaction *transaction,
 			   const char *refname,
 			   const struct object_id *new_oid,
 			   const struct object_id *old_oid,
+			   const char *new_target,
+			   const char *old_target,
 			   unsigned int flags, const char *msg,
 			   struct strbuf *err);
 

refs/files-backend.c

@@ -1198,7 +1198,7 @@ static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
 	ref_transaction_add_update(
 			transaction, r->name,
 			REF_NO_DEREF | REF_HAVE_NEW | REF_HAVE_OLD | REF_IS_PRUNING,
-			null_oid(), &r->oid, NULL);
+			null_oid(), &r->oid, NULL, NULL, NULL);
 	if (ref_transaction_commit(transaction, &err))
 		goto cleanup;
 
@@ -1292,7 +1292,7 @@ static int files_pack_refs(struct ref_store *ref_store,
 		 * packed-refs transaction:
 		 */
 		if (ref_transaction_update(transaction, iter->refname,
-					   iter->oid, NULL,
+					   iter->oid, NULL, NULL, NULL,
 					   REF_NO_DEREF, NULL, &err))
 			die("failure preparing to create packed reference %s: %s",
 			    iter->refname, err.buf);
@@ -2309,7 +2309,7 @@ static int split_head_update(struct ref_update *update,
 			transaction, "HEAD",
 			update->flags | REF_LOG_ONLY | REF_NO_DEREF,
 			&update->new_oid, &update->old_oid,
-			update->msg);
+			NULL, NULL, update->msg);
 
 	/*
 	 * Add "HEAD". This insertion is O(N) in the transaction
@@ -2372,7 +2372,7 @@ static int split_symref_update(struct ref_update *update,
 	new_update = ref_transaction_add_update(
 			transaction, referent, new_flags,
 			&update->new_oid, &update->old_oid,
-			update->msg);
+			NULL, NULL, update->msg);
 
 	new_update->parent_update = update;
 
@@ -2763,7 +2763,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 					packed_transaction, update->refname,
 					REF_HAVE_NEW | REF_NO_DEREF,
 					&update->new_oid, NULL,
-					NULL);
+					NULL, NULL, NULL);
 		}
 	}
 
@@ -3048,7 +3048,7 @@ static int files_initial_transaction_commit(struct ref_store *ref_store,
 		ref_transaction_add_update(packed_transaction, update->refname,
 					   update->flags & ~REF_HAVE_OLD,
 					   &update->new_oid, &update->old_oid,
-					   NULL);
+					   NULL, NULL, NULL);
 	}
 
 	if (packed_refs_lock(refs->packed_ref_store, 0, err)) {