"Bad request" for array parameter with union type

[chriscpty]

Take a yii\web\Controller with an example action like this:

    public function actionFoo(int|array $bar) {
        return $this->asJson(['foo' => $bar]);
    }

Expected result: calling this action with a single query parameter (like /foo?bar=1) and calling it with an array query parameter (like foo?bar[]=1&bar[]=2) both work.

Actual result: Calling it with an integer parameter works correctly, calling it with an array parameter returns a 400 Bad Request.

I'm pretty sure the problem lies with this portion of yii\web\Controller::bindActionParams (line 136 and onwards):

$isArray = ($type = $param->getType()) instanceof \ReflectionNamedType && $type->getName() === 'array';
if ($isArray) {
 $params[$name] = (array)$params[$name];
} elseif (is_array($params[$name])) {
 $isValid = false;
} elseif (
  // ...

$isArray does not check for whether $type is a ReflectionUnionType that includes array, hence the array parameter is wrongly rejected.