Language: property hook duplicate backing property names must fail compile (Zend/zend_compile.c)

Problem

PHP 8.4 property hooks declare a public hooked property and a private backing field with the same name inside one class. Zend rejects duplicate property declarations at compile time.

This compiler accepts the pattern and runs:

class C {
    public int $x { get => $this->x; set => $this->x = $value; }
    public string $y = 'a';
    private int $x = 1; // duplicate name — must be compile error
}

VM today prints compile-ok x=1 y=a; Zend must not compile.

php-src reference

php/php-src Zend/zend_compile.c — property hook desugaring + duplicate property name check
php/php-src Zend/zend_property_hooks.c — backing storage layout

Repro

test/repro/maintainer_gap_property_hook_multi_property_redeclare.php:

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php test/repro/maintainer_gap_property_hook_multi_property_redeclare.php 2>&1 | tail -2
php bin/vm.php test/repro/maintainer_gap_property_hook_multi_property_redeclare.php 2>&1 | tail -2
'

Runtime	Result
Zend PHP 8.4+	compile error (duplicate property `$x`)
VM today	`compile-ok x=1 y=a` ❌

Scope (PHP-in-PHP)

Path	Work
`lib/Compiler.php`	after hook lowering, detect duplicate property names in CE
`lib/SourcePreprocessor/PropertyHooks.php`	align backing name rules with zend_compile
Tests	`test/compliance/cases/language/property_hook_duplicate_name.phpt`

Done when (php-src-strict)

Repro fails compile on VM with Zend-matching message
Valid hook + distinct backing patterns from php-src tests still compile
./script/ci-fast.sh --filter property_hook_duplicate green

Language: PHP 8.4 property hooks — get/set on properties (Zend parity) #3145 property hooks · Language: readonly property with hooks — compile rejects valid PHP 8.4 pattern (Zend/zend_compile.c) #9835 readonly+hooks compile · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

claim: cursor-agent-lane-b — starting this run

claim: cursor-agent-lane-b — implementing detached same-name backing compile gate (#10393)

Fix property hook detached same-name backing as duplicate compile err…

Merged via #10420.

Fix: Removed detached same-name backing field merge in PropertyHooks (#9673/#9831). Only immediately-adjacent backing fields still merge (#7031). Detached private $x after other properties now hits compiler Cannot redeclare C::$x matching zend_compile.c.

Verification:

php bin/vm.php test/repro/maintainer_gap_property_hook_multi_property_redeclare.php
# parseAndCompile failure: Cannot redeclare C::$x (exit 255)

./vendor/bin/phpunit test/compliance/ --filter property_hook_duplicate_name
# OK

Language: merge detached property-hook backing past sibling members (#…

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Language: property hook duplicate backing property names must fail compile (Zend/zend_compile.c) #10393

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php-src reference

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Done when (php-src-strict)

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Language: property hook duplicate backing property names must fail compile (Zend/zend_compile.c) #10393

Description

Category

Problem

php-src reference

Repro

Scope (PHP-in-PHP)

Done when (php-src-strict)

Related

Activity

PurHur commented on Jun 21, 2026

PurHur commented on Jun 21, 2026

PurHur commented on Jun 21, 2026

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