PHP 8.4 | Implicitly nullable deprecation ignores null in constant expressions in default value

[jrfnl]

Description

The following code:

<?php
define('MY_CONST', false);
function constantExpressionInDefault( int $a = MY_CONST ? 10 : NULL) {}

Resulted in this output:

But I expected this output instead:

Deprecated: Implicitly marking parameter $paramA as nullable is deprecated, the explicit nullable type must be used instead in ... on line 3

Demo:

• https://3v4l.org/26TbS/rfc#vgit.master
• https://3v4l.org/26TbS#veol

Context

I was doing some experimenting with the new deprecation as introduced in #12959 for the PHPCompatibility sniff to detect this via static analysis.

Not sure if this behaviour is intentional or a bug, but I figured I should flag it, so you all could have a look at it and take a decision on what should be done with parameters declared like the above example.

/cc @kocsismate @Girgias

PHP Version

master

Operating System

N/A

[iluuu1994]

It's not actually nullable, though: https://3v4l.org/WA5d4

[jrfnl]

@iluuu1994 Good point, though that feels like an oversight/bug in how the original exception for typed parameters with a null default value was implemented: https://3v4l.org/M2v0D/rfc#vgit.master

Makes me all the happier that this exception is now being deprecated.

[iluuu1994]

@jrfnl The problem is that the type is decided at compile time. So if the expression isn't fully evaluable at compile time, there's no guaranteed way to know if the expression may evaluate to null.

[iluuu1994]

But yes, I don't disagree that the behavior was suboptimal 🙂 https://3v4l.org/QkjST

[jrfnl]

https://3v4l.org/QkjST

Ouch...

[iluuu1994]

@jrfnl Are you ok closing this then? This issue can never be solved in full, as explained above.