Language: clone() on readonly objects — deep copy + readonly property guards (Zend zend_clones.c parity) #3430

Category

language

Problem

clone $obj today uses ObjectEntry::cloneShallow() (lib/VM/ObjectEntry.php) — copies property values but does not implement Zend rules for:

• readonly classes — clone must produce a new object with readonly semantics preserved
• readonly instance properties — cloned object must not allow illegal writes
• User __clone() hook (Language: __clone magic method — invoke user hook on clone (Zend parity) #3170) — invoke after shallow copy, before __construct re-run is skipped

php-src reference

• Zend/zend_clones.c — zend_clone_obj, readonly clone restrictions
• Zend/zend_object_handlers.c — clone_obj handler, property separation
• Zend/zend_compile.c — ZEND_CLONE opcode

Repro

<?php
readonly class Box {
    public function __construct(public string $v) {}
}
$a = new Box('a');
$b = clone $a;
$b->v = 'b'; // Zend: Error Cannot modify readonly property
echo $b->v;

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

Zend: third line throws on $b->v = 'b'. This compiler: verify clone creates independent object and readonly write still fatal.

Scope

• lib/VM.php — OpCode::TYPE_CLONE (currently cloneShallow only)
• lib/VM/ObjectEntry.php — property separation for objects/arrays
• lib/VM.php — call __clone when defined (Language: __clone magic method — invoke user hook on clone (Zend parity) #3170)
• Tests: test/compliance/cases/language/clone_readonly_class.phpt

Done when

• Repro: modifying clone of readonly property fatals like Zend
• Non-readonly classes: clone is independent copy (nested array copy subset documented if deferred)
• ./script/ci-fast.sh --filter clone_readonly green

Related

• Language: readonly classes (PHP 8.2+) #1360 readonly classes · Language: __clone magic method — invoke user hook on clone (Zend parity) #3170 __clone · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492