bug #20931 [VarDumper] Fix dumping by-ref variadics (nicolas-grekas)

This PR was merged into the 2.7 branch.

Discussion
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[VarDumper] Fix dumping by-ref variadics

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

The correct php syntax is `&...$foo`, not ~~`...&$foo`~~

Commits
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28ec361 [VarDumper] Fix dumping by-ref variadics

src/Symfony/Component/VarDumper/Caster/ReflectionCaster.php

@@ -125,12 +125,12 @@ public static function castFunctionAbstract(\ReflectionFunctionAbstract $c, arra
 
         foreach ($c->getParameters() as $v) {
             $k = '$'.$v->name;
-            if ($v->isPassedByReference()) {
-                $k = '&'.$k;
-            }
             if (method_exists($v, 'isVariadic') && $v->isVariadic()) {
                 $k = '...'.$k;
             }
+            if ($v->isPassedByReference()) {
+                $k = '&'.$k;
+            }
             $a[$prefix.'parameters'][$k] = $v;
         }