update-ref: allow creation of multiple transactions

While git-update-ref has recently grown commands which allow interactive
control of transactions in e48cf33b61 (update-ref: implement interactive
transaction handling, 2020-04-02), it is not yet possible to create
multiple transactions in a single session. To do so, one currently still
needs to invoke the executable multiple times.

This commit addresses this shortcoming by allowing the "start" command
to create a new transaction if the current transaction has already been
either committed or aborted.

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

Documentation/git-update-ref.txt

@@ -125,7 +125,8 @@ option::
 start::
 	Start a transaction. In contrast to a non-transactional session, a
 	transaction will automatically abort if the session ends without an
-	explicit commit.
+	explicit commit. This command may create a new empty transaction when
+	the current one has been committed or aborted already.
 
 prepare::
 	Prepare to commit the transaction. This will create lock files for all

builtin/update-ref.c

@@ -446,7 +446,18 @@ static void update_refs_stdin(void)
 			state = cmd->state;
 			break;
 		case UPDATE_REFS_CLOSED:
-			die("transaction is closed");
+			if (cmd->state != UPDATE_REFS_STARTED)
+				die("transaction is closed");
+
+			/*
+			 * Open a new transaction if we're currently closed and
+			 * get a "start".
+			 */
+			state = cmd->state;
+			transaction = ref_transaction_begin(&err);
+			if (!transaction)
+				die("%s", err.buf);
+
 			break;
 		}
 

t/t1400-update-ref.sh

@@ -1533,4 +1533,54 @@ test_expect_success 'transaction with prepare aborts by default' '
 	test_must_fail git show-ref --verify -q $b
 '
 
+test_expect_success 'transaction can commit multiple times' '
+	cat >stdin <<-EOF &&
+	start
+	create refs/heads/branch-1 $A
+	commit
+	start
+	create refs/heads/branch-2 $B
+	commit
+	EOF
+	git update-ref --stdin <stdin >actual &&
+	printf "%s: ok\n" start commit start commit >expect &&
+	test_cmp expect actual &&
+	echo "$A" >expect &&
+	git rev-parse refs/heads/branch-1 >actual &&
+	test_cmp expect actual &&
+	echo "$B" >expect &&
+	git rev-parse refs/heads/branch-2 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'transaction can create and delete' '
+	cat >stdin <<-EOF &&
+	start
+	create refs/heads/create-and-delete $A
+	commit
+	start
+	delete refs/heads/create-and-delete $A
+	commit
+	EOF
+	git update-ref --stdin <stdin >actual &&
+	printf "%s: ok\n" start commit start commit >expect &&
+	test_must_fail git show-ref --verify refs/heads/create-and-delete
+'
+
+test_expect_success 'transaction can commit after abort' '
+	cat >stdin <<-EOF &&
+	start
+	create refs/heads/abort $A
+	abort
+	start
+	create refs/heads/abort $A
+	commit
+	EOF
+	git update-ref --stdin <stdin >actual &&
+	printf "%s: ok\n" start abort start commit >expect &&
+	echo "$A" >expect &&
+	git rev-parse refs/heads/abort >actual &&
+	test_cmp expect actual
+'
+
 test_done