improve FormType::getType exception message details

Author: Nicals

FormRegistry.php

@@ -84,11 +84,14 @@ public function getType($name)
 
             if (!$type) {
                 // Support fully-qualified class names
-                if (class_exists($name) && in_array('Symfony\Component\Form\FormTypeInterface', class_implements($name))) {
-                    $type = new $name();
-                } else {
-                    throw new InvalidArgumentException(sprintf('Could not load type "%s"', $name));
+                if (!class_exists($name)) {
+                    throw new InvalidArgumentException(sprintf('Could not load type "%s": class does not exist.', $name));
                 }
+                if (!in_array(FormTypeInterface::class, class_implements($name))) {
+                    throw new InvalidArgumentException(sprintf('Could not load type "%s": class does not implement "%s".', $name, FormTypeInterface::class));
+                }
+
+                $type = new $name();
             }
 
             $this->resolveAndAddType($type);