Cover possible no-db related throw before touching the db

Address #6545 (comment)

Author: simPod

src/Connection.php

@@ -9,6 +9,7 @@
 use Doctrine\DBAL\Cache\QueryCacheProfile;
 use Doctrine\DBAL\Driver\API\ExceptionConverter;
 use Doctrine\DBAL\Driver\Connection as DriverConnection;
+use Doctrine\DBAL\Driver\Exception as TheDriverException;
 use Doctrine\DBAL\Driver\ServerInfoAwareConnection;
 use Doctrine\DBAL\Driver\Statement as DriverStatement;
 use Doctrine\DBAL\Event\TransactionBeginEventArgs;
@@ -1291,7 +1292,20 @@ public function transactional(Closure $func)
             }
         }
 
-        $this->commit();
+        $shouldRollback = true;
+        try {
+            $this->commit();
+
+            $shouldRollback = false;
+        } catch (TheDriverException $t) {
+            $shouldRollback = false;
+
+            throw $t;
+        } finally {
+            if ($shouldRollback) {
+                $this->rollBack();
+            }
+        }
 
         return $res;
     }

tests/ConnectionTest.php

@@ -1025,6 +1025,28 @@ public function rollBack(): void
             self::assertSame('Original exception', $e->getPrevious()->getMessage());
         }
     }
+
+    /**
+     * We are not sure if this can happen in real life scenario
+     */
+    public function testItFailsDuringCommitBeforeTouchingDb(): void
+    {
+        $connection = new class (['memory' => true], new Driver\SQLite3\Driver()) extends Connection {
+            public function commit(): void
+            {
+                throw new Exception('Fail before touching the db');
+            }
+
+            public function rollBack(): void
+            {
+                throw new Exception('Rollback got triggered');
+            }
+        };
+
+        $this->expectExceptionMessage('Rollback got triggered');
+        $connection->transactional(static function (): void {
+        });
+    }
 }
 
 interface ConnectDispatchEventListener