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#[\NoDiscard] with PHP function version of call_user_func() does not produce any warning. #25028
Closed as not planned
Description
Description
The following code:
<?php
#[\NoDiscard]
function test(): int {
return 0;
}
if (random_int(1,1)) {
$fn = 'call_user_func';
} else {
$fn = 'nope';
}
$fn('test');Resulted in this output:
But I expected this output instead:
Warning: The return value of function test() should either be used or intentionally ignored by casting it as (void) in %s on line %d
The root cause is that there is no handling of a potential #[\NoDiscard] attribute in the PHP_FUNCTION(call_user_func) version. I'm guessing this also not handled in PHP_FUNCTION(call_user_func_array), PHP_FUNCTION(forward_static_call), and PHP_FUNCTION(forward_static_call_array).
PHP Version
PHP 8.5 and above
Operating System
No response
Activity
TimWolla commentedon Oct 29, 2026
This is working as designed: Internally
call_user_func()is consuming the return value oftest()- it's just that the return value ofcall_user_func()is unused and we cannot make the attribute conditional.ndossche commentedon Oct 29, 2026
I agree with your reasoning, but note that due to the optimizer, the behaviour changes: https://3v4l.org/oJ3IK#v
TimWolla commentedon Oct 29, 2026
Yes, I'm aware. I would consider that to be one of the acceptable behavioral differences introduced by optimization. Technically the optimizer could emit a
(void)cast there, but that is probably not worth it, particularly sincecall_user_func()is likely rarely used in modern code (due to more ergonomic alternatives).Girgias commentedon Oct 29, 2026
Sure, I don't have strong feelings about it. Will close as won't fix.