Regression: ?? on property hooks invokes get hook when backing initialized (re-#8902, zend_property_hooks.c)

[PurHur]

Category

language · regression · php-src-strict

Problem

Closed #8902 required ?? on hooked properties to check backing initialization without calling the get hook. VM regressed (2026-06-16): $c->x ?? 'default' invokes a throwing get hook even when separate backing holds 'a'.

php-src reference

• php/php-src Zend/zend_property_hooks.c — coalesce / isset fast path
• php/php-src Zend/zend_compile.c — ZEND_AST_COALESCE on hooked properties

Repro

test/repro/issue_property_hook_coalesce.php:

<?php
class C {
    public string $x {
        get { throw new Exception('get must not run for ??'); }
        set => $this->backing = $value;
    }
    private string $backing = 'a';
}
$c = new C();
var_dump($c->x ?? 'default');
echo "ok\n";

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php test/repro/issue_property_hook_coalesce.php
php bin/vm.php test/repro/issue_property_hook_coalesce.php
'

Runtime	Expected	Observed
Zend 8.4+	string(1) "a" + ok	—
VM	same	Fatal: get must not run for ??

Scope

• lib/VM.php — ??= / coalesce on hooked properties (~Language: ??= on property hooks must invoke get/set hooks (zend_property_hooks.c) #6472 comment)
• lib/JIT/ — coalesce lowering when property has hooks
• test/compliance/cases/language/property_hook_coalesce.phpt

Done when

• Repro prints string(1) "a" and ok on VM
• Uninitialized backing uses right-hand default without get hook
• Shares probe with Language: isset() on property hooks must not invoke get hook (zend_property_hooks.c, php-src-strict) #8917 / Regression: empty() on property hooks invokes get hook (re-#8901, zend_property_hooks.c) #8918 (empty)

Links

• Language: ?? on property hooks must not invoke get hook when backing is initialized (zend_property_hooks.c) #8902 (closed) · Language: isset() on property hooks must not invoke get hook (zend_property_hooks.c, php-src-strict) #8917 · Regression: empty() on property hooks invokes get hook (re-#8901, zend_property_hooks.c) #8918 · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: worker-lane-c — starting this run (Lane C queue empty — all %3==2 issues are stdlib/php-in-php; continuing property-hooks cluster after #8918)

[PurHur]

Merged via #8934.

The VM regression was already fixed on master by #8915 (fetchObjectPropertyForCoalesce / propertyHookCoalesceRead) and #8923 (func-call arg coalesce). This PR adds PropertyHookCoalesceTest unit guard alongside the isset/empty tests from #8917/#8918.

Verification (Docker):

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php bin/vm.php test/repro/issue_property_hook_coalesce.php
php vendor/bin/phpunit test/unit/PropertyHookCoalesceTest.php
php vendor/bin/phpunit test/compliance/VMTest.php --filter property_hook_coalesce
'

• Issue repro: string(1) "a" + ok + string(7) "default" + unset ok
• Unit + compliance guards green