Language: foreach by-ref on enum case elements — must preserve enum objects not coerce to int (Zend/zend_enum.c)

[PurHur]

Category

language · php-src-strict

Problem

When iterating an array of enum cases by reference (foreach ($arr as &$v)), Zend preserves enum case objects (E debug type) and assignment through the reference updates the enum case in the array. This compiler coerces enum cases to backing int scalars during by-ref foreach, breaking enum identity semantics.

php-src reference

• php/php-src Zend/zend_execute.c — ZEND_FE_FETCH_R / by-ref fetch on enum objects
• php/php-src Zend/zend_enum.c — enum object identity (not unwrapped to scalar in foreach)

Repro (failure today)

test/repro/maintainer_gap_foreach_byref_enum.php:

<?php
declare(strict_types=1);

enum E: int { case A = 1; case B = 2; }

foreach ([E::A, E::B] as &$v) {
    echo get_debug_type($v), "\n";
    $v = E::B;
    break;
}
echo get_debug_type($v), "\n";

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php8.2 test/repro/maintainer_gap_foreach_byref_enum.php
php bin/vm.php test/repro/maintainer_gap_foreach_byref_enum.php
'

Line	Zend PHP 8.1+	VM today
loop body type	E	int
after loop $v type	E	int

Scope (PHP-in-PHP)

Path	Work
lib/VM.php	foreach by-ref fetch must not scalarize enum cases
lib/JIT/IteratorHelper.php	by-ref iterator protocol parity when JIT lowers foreach
Tests	test/compliance/cases/language/foreach_byref_enum.phpt

Done when (php-src-strict)

• Repro prints E twice on VM
• Array slot updated through $v retains enum case object identity
• JIT foreach agrees when in scope

Related

• Language: property hook foreach by-reference on get-only hook — must Error before loop body (re-#6435, Zend/zend_property_hooks.c) #9761 property-hook foreach by-ref · php-in-php: JIT IteratorHelper — route foreach iterator protocol through VmIterator PHP not ~725-line LLVM (#1492) #10080 IteratorHelper php-in-PHP · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

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

[PurHur]

Merged via #10156.

Finding: foreach by-ref enum case identity was already correct on VM/JIT (fixed in #5657; also covered by foreach_enum_case_by_ref.phpt and enum_value_contexts.phpt).

Added: dedicated compliance guard test/compliance/cases/language/foreach_byref_enum.phpt matching this issue's inline-array + break repro.

Verification:

php vendor/bin/phpunit --filter foreach_byref_enum  → OK (3 tests)
php bin/vm.php test/repro/maintainer_gap_foreach_byref_enum.php  → E / E
php bin/jit.php test/repro/maintainer_gap_foreach_byref_enum.php  → E / E