Funnily enough, the following works in PHP 5.3, but it is a syntax error in all later versions where call-time pass-by-reference has been removed:

$a->func( &$b );

https://3v4l.org/EOJ07

We noticed the issue in code review of https://gerrit.wikimedia.org/r/c/mediawiki/extensions/DiscussionTools/+/704835. I think it's an unavoidable limitation of __call (per PHP documentation: "None of the arguments of these magic methods can be passed by reference."), but @DannyS712 asked me to file a bug.

Using ReflectionClass / ReflectionMethod directly, we get the same error when doing the following:

$class = new ReflectionClass( A::class );
$func = $class->getMethod( 'func' );
$func->setAccessible( true );
$func->invokeArgs( null, [ $b ] );
echo $b;

…while the following works correctly:

$func->invokeArgs( null, [ &$b ] );

But even if you could determine at runtime which arguments need to be passed as references (seems tricky, ReflectionMethod doesn't seem to have a way to do it; you can maybe parse the output of __toString(), but it's probably a bad idea), you still can't make the arguments of the __call function behave like references.

I tried testing this out, and while you can pass references to the invokeArgs method, the testing access wrapper works by using a __call handler, and the parameters to that are never passed by reference (https://www.php.net/manual/en/language.oop5.overloading.php as noted above)

Perhaps we should add a functionality to TestingAccessWrapper to support calling method that require passing by reference, by using a dedicated method instead of __call ?

$obj = TestingAccessWrapper::newFromClass( Demo::class );
$obj->_callWithReference( 'targetMethod', [ $a, &$b ] );

would invoke Demo::targetMethod with $a and &$b as the parameters - its a bit uglier than how we using TestingAccessWrapper now, where we just call the desired private method, but it should support references.

This would also be useful in core[1] where the failure of TestingAccessWrapper to handle static params was worked around by using ReflectionClass/ReflectionMethod directly.

[1] https://gerrit.wikimedia.org/g/mediawiki/core/+/9dd696882db5117040ce9b38eb235c33270c4407/tests/phpunit/includes/session/SessionManagerTest.php#913

I encountered this with writing tests for CheckUser. Worked around it by doing the reflection in the test itself.

Change 955985 had a related patch set uploaded (by D3r1ck01; author: Derick Alangi):

[testing-access-wrapper@master] TestingAccessWrapper: Support passing arguments by reference

https://gerrit.wikimedia.org/r/955985

Change 955985 abandoned by D3r1ck01:

[testing-access-wrapper@master] TestingAccessWrapper: Support passing arguments by reference

Reason:

See discussion on patch.

https://gerrit.wikimedia.org/r/955985