Fix GH-10497: Allow const obj->prop = value

[khaledalam]

Description

Fixes #10497 - Allows direct modification of object properties stored in constants.

Problem

Previously, this code would fail with a fatal error:

const a = new stdClass;
a->b = 42;  // Fatal error: Cannot use temporary expression in write context

Solution

Modified the compiler to properly handle ZEND_AST_CONST in variable compilation contexts:

Constants now emit IS_VAR instead of IS_TMP_VAR when used in write contexts
This allows property assignment opcodes to work correctly with constant objects

Tests:

• Added Zend/tests/gh10497.phpt - comprehensive test for the fix
• Updated Zend/tests/gh12102_3.phpt - reflects improved constant handling

Behavior

Now supports all property operations on constant objects:

const obj = new stdClass;
obj->prop = 'value';
obj->prop = 'new value';
obj->another = 'test';
obj->counter = 0;
obj->counter++;
obj->num = 10;
obj->num += 5;
unset(obj->prop);
obj->nested = new stdClass;
obj->nested->value = 123;

The constant reference remains immutable, but the object itself is mutable as expected.

[iluuu1994]

Thanks @khaledalam! Looks reasonable overall.

[khaledalam]

Thanks @khaledalam! Looks reasonable overall.

Thanks @iluuu1994 for the feedback, all comments addressed.

[iluuu1994]

Cool, thanks @khaledalam! This is a language change and should be discussed on the internals mailing list at least. I think this will impact GH-13800, but that's not a major issue.

[iluuu1994]

Btw, one thing in particular people might object to is:

const arrayTest = [1, 2, 3];
arrayTest[] = 4;
var_dump(arrayTest);

This becomes valid, but prints:

array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
}

I.e. the assignment has no effect, because it happens on a temporary value. Make sure to mention this in your e-mail to internals.

[khaledalam]

I've opened an internals thread and sent an email for discussion: https://news-web.php.net/php.internals/129757

[iluuu1994]

It sounds like @TimWolla objected, so this would need an RFC, or at least the mitigation from https://news-web.php.net/php.internals/129839.

[TimWolla]

Yes, my replies on the list were an objection against the PR as-is. Selecting request changes for visibility.

[khaledalam]

Noted, I'll look into it