[TypeDeclaration] Skip redundant intersection types in union return types

[kevin9327]

ReturnUnionTypeRector can add a return type that PHP won't compile. If a value narrowed by instanceof is returned on one branch and the un-narrowed value on another, the inferred union contains both A and A&B, and both get printed:

public function run(\Iterator $obj)
{
    if (! $obj instanceof \Countable) {
        return $obj;
    }

    if (rand(0, 1)) {
        return $obj;
    }

    return '10';
}

becomes

public function run(\Iterator $obj): \Iterator|(\Countable&\Iterator)|string

and loading the file fails with:

PHP Fatal error:  Type Countable&Iterator is redundant as it is more restrictive than type Iterator

I found this by running Rector, with the PHP 8.4 set and the prepared sets, over laravel/framework, composer, guzzle, doctrine/orm and symfony/console, then running php -l on every changed file. It was the only file that stopped compiling: Illuminate\Log\LogManager::prepareHandler() got HandlerInterface|FingersCrossedHandler|(HandlerInterface&FormattableHandlerInterface)|(FingersCrossedHandler&FormattableHandlerInterface).

UnionTypeMapper::matchPhpParserUnionType() now drops any intersection member that contains every part of another member, whether that member is a single class or a smaller intersection. This is the same name-based check PHP runs at compile time. In the example above the result is \Iterator|string.

The new fixture FixtureUnionIntersection/redundant_intersection.php.inc fails without the change. The full vendor/bin/phpunit suite passes, and ECS and PHPStan report nothing new for the changed file.

[samsonasik]

Looks good

[TomasVotruba]

Thanks