[Mailer] Catch missing scheme in DSN.

Author: derrabus

Tests/TransportTest.php

@@ -69,11 +69,18 @@ public function testFromInvalidDsn()
         Transport::fromDsn('some://');
     }
 
+    public function testNoScheme()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('The "//sendmail" mailer DSN must contain a transport scheme.');
+        Transport::fromDsn('//sendmail');
+    }
+
     public function testFromInvalidDsnNoHost()
     {
         $this->expectException(InvalidArgumentException::class);
-        $this->expectExceptionMessage('The "?!" mailer DSN must contain a mailer name.');
-        Transport::fromDsn('?!');
+        $this->expectExceptionMessage('The "file:///some/path" mailer DSN must contain a mailer name.');
+        Transport::fromDsn('file:///some/path');
     }
 
     public function testFromInvalidTransportName()

Transport.php

@@ -64,6 +64,10 @@ private static function createTransport(string $dsn, EventDispatcherInterface $d
             throw new InvalidArgumentException(sprintf('The "%s" mailer DSN is invalid.', $dsn));
         }
 
+        if (!isset($parsedDsn['scheme'])) {
+            throw new InvalidArgumentException(sprintf('The "%s" mailer DSN must contain a transport scheme.', $dsn));
+        }
+
         if (!isset($parsedDsn['host'])) {
             throw new InvalidArgumentException(sprintf('The "%s" mailer DSN must contain a mailer name.', $dsn));
         }