[PropertyAccess][DX] Enhance exception that say that some methods are missing if they don't

Author: nykopol

src/Symfony/Component/PropertyAccess/PropertyAccessor.php

@@ -714,6 +714,17 @@ private function getWriteAccessInfo($class, $property, $value)
                     // we call the getter and hope the __call do the job
                     $access[self::ACCESS_TYPE] = self::ACCESS_TYPE_MAGIC;
                     $access[self::ACCESS_NAME] = $setter;
+                } elseif (null !== $methods = $this->findAdderAndRemover($reflClass, $singulars)) {
+                    $access[self::ACCESS_TYPE] = self::ACCESS_TYPE_NOT_FOUND;
+                    $access[self::ACCESS_NAME] = sprintf(
+                        'The property "%s" in class "%s" can be defined with the methods "%s()" but '.
+                        'the new value must be an array or an instance of \Traversable, '.
+                        '"%s" given.',
+                        $property,
+                        $reflClass->name,
+                        implode('()", "', $methods),
+                        is_object($value) ? get_class($value) : gettype($value)
+                    );
                 } else {
                     $access[self::ACCESS_TYPE] = self::ACCESS_TYPE_NOT_FOUND;
                     $access[self::ACCESS_NAME] = sprintf(

src/Symfony/Component/PropertyAccess/Tests/PropertyAccessorCollectionTest.php

@@ -194,4 +194,15 @@ public function testIsWritableReturnsFalseIfNoAdderNorRemoverExists()
 
         $this->assertFalse($this->propertyAccessor->isWritable($car, 'axes', $axes));
     }
+
+    /**
+     * @expectedException \Symfony\Component\PropertyAccess\Exception\NoSuchPropertyException
+     * expectedExceptionMessageRegExp /The property "axes" in class "Mock_PropertyAccessorCollectionTest_Car[^"]*" can be defined with the methods "addAxis()", "removeAxis()" but the new value must be an array or an instance of \Traversable, "string" given./
+     */
+    public function testSetValueFailsIfAdderAndRemoverExistButValueIsNotTraversable()
+    {
+        $car = $this->getMock(__CLASS__.'_Car');
+
+        $this->propertyAccessor->setValue($car, 'axes', 'Not an array or Traversable');
+    }
 }