feature symfony#24277 [Serializer] Getter for extra attributes in ExtraAttributesException (mdeboer)

This PR was squashed before being merged into the 3.4 branch (closes symfony#24277).

Discussion
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[Serializer] Getter for extra attributes in ExtraAttributesException

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes (failure unrelated)
| Fixed tickets |
| License       | MIT

This PR adds a public getter for the extra attributes in `ExtraAttributesException` and makes it easier to create custom exception messages (e.g. JSON formatted).

Commits
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cb935e7 [Serializer] Getter for extra attributes in ExtraAttributesException

Author: ogizanagi

src/Symfony/Component/Serializer/CHANGELOG.md

@@ -7,6 +7,7 @@ CHANGELOG
  * added `AbstractObjectNormalizer::DISABLE_TYPE_ENFORCEMENT` context option
    to disable throwing an `UnexpectedValueException` on a type mismatch
  * added support for serializing `DateInterval` objects
+ * added getter for extra attributes in `ExtraAttributesException`
 
 3.3.0
 -----

src/Symfony/Component/Serializer/Exception/ExtraAttributesException.php

@@ -18,10 +18,24 @@
  */
 class ExtraAttributesException extends RuntimeException
 {
+    private $extraAttributes;
+
     public function __construct(array $extraAttributes, \Exception $previous = null)
     {
         $msg = sprintf('Extra attributes are not allowed ("%s" are unknown).', implode('", "', $extraAttributes));
 
+        $this->extraAttributes = $extraAttributes;
+
         parent::__construct($msg, 0, $previous);
     }
+
+    /**
+     * Get the extra attributes that are not allowed.
+     *
+     * @return array
+     */
+    public function getExtraAttributes()
+    {
+        return $this->extraAttributes;
+    }
 }