Language: empty() on property hooks must not invoke get hook (zend_property_hooks.c)

[PurHur]

Category

language · php-src-strict

Problem

On PHP 8.4 property hooks, empty($obj->hooked) must use the same isset-style backing check as Zend and must not call the get hook. This compiler invokes the get hook, so a throwing getter fatals instead of returning false.

Distinct from #5203 (get_object_vars must call get hooks) — empty()/isset() are the inverse rule.

php-src reference

• php/php-src Zend/zend_property_hooks.c — zend_isset_property_ex / empty semantics
• php/php-src Zend/zend_operators.c — empty opcode on hooked properties

Repro

Save as test/repro/issue_property_hook_empty.php:

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

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

Runtime	Output
Zend PHP 8.4+	bool(false) then ok (backing initialized; get hook not called)
VM (wrong)	Fatal error: Uncaught Exception: get must not run for empty()

Scope (PHP-in-PHP)

Layer	Path
VM	lib/VM.php — OP_EMPTY / isset path for hooked properties; reuse hook-backing probe used by ??= (#6472)
Compiler	No syntax change
JIT/AOT	Mirror isset/empty hook guard when lowering exists
Tests	test/compliance/cases/language/property_hook_empty.phpt

Done when (php-src-strict)

• Repro prints bool(false) + ok on VM without invoking get hook
• empty($obj->virtualGetOnly) on write-only virtual hook matches Zend Error/behavior
• ./script/ci-fast.sh --filter property_hook_empty green

Related

#8870 foreach by-ref hooks · #5203 get_object_vars hooks · #6484 write-only reads · #1492

[PurHur]

claim: worker-lane-b — starting this run

[PurHur]

Merged via #8910.

VM: emptyObjectProperty() probes separate hook backing via emptyHookedPropertyViaSeparateBacking() (same isset-style rule as ??= / #6472) — get hook is not invoked when setBacking/getBacking points at a distinct field.

Compiler: Hoisted empty()/isset() producers used as call arguments (e.g. var_dump(empty($c->x))) now emit TYPE_EMPTY_OBJECT_PROPERTY / TYPE_ISSET instead of dead arg slots.

Verification (green):

./script/docker-exec.sh -- bash -lc 'php bin/vm.php test/repro/issue_property_hook_empty.php'
# bool(false)\nok

./script/docker-exec.sh -- bash -lc './vendor/bin/phpunit --filter property_hook_empty'
# OK (1 test)

./script/docker-exec.sh -- bash -lc './vendor/bin/phpunit --filter property_hook_isset'
# OK (1 test)