Implement GH-18261: Allow cast to be used in constant expressions

[nielsdos]

No description provided.

[iluuu1994]

I think the object cast is problematic. This will lead to an incorrect result.

class C {
    public $prop = (object) [];
}

$c = new C;
$c->prop->x = 42;
var_dump(new C);

[nielsdos]

I remember from the RECV_INIT case that we always re-evaluate refcounted values (

php-src/Zend/zend_vm_def.h

Line 5728 in ac9392b

/* we keep in cache only not refcounted values */

), of course this particular situation is different but I assumed this held in general.

The code your provided doesn't execute though. I presume you meant (object) [], in which case there is indeed a problem.

[nielsdos]

We could ban the object cast from constant evaluation (which should be rare anyway), or find a workaround. I think the former (banning it) seems more reasonable. WDYT?

[iluuu1994]

I agree that object cast should simply be forbidden. This feature is not worth changing how we evaluate property constant expressions.

[bwoebi]

@iluuu1994 Should it not be treated the same than https://wiki.php.net/rfc/new_in_initializers simply? At least that's what I'd expect.
Doing new stdClass or (object) [] is in the exact same vein.

[iluuu1994]

@bwoebi If @nielsdos wants to add this support, I'm fine with it. Importantly, zend_ast_evaluate_ctx.had_side_effects still needs to be set to false so that we don't have erroneous caching for RECV_INIT. In this case, static properties and class constants would technically be fine, since the cast does not have any side-effects.

[mvorisek]

Test with warning like https://3v4l.org/6ugOa should be added.

IDK if exception is possible, if so, it should be tested as well.

[iluuu1994]

Exceptions are at least possible with (string) $nonStringable, there might be others.