Language: enum case identity comparison — == / === / <=> must not coerce backing scalars (Zend/zend_enum.c)

[PurHur]

Category

language · php-src-strict

Problem

Comparing two distinct backed enum cases must use enum identity rules: == / === are false for different cases; <=> compares backing values. VM coerces cases to backing scalars and returns wrong results (E::A == E::B is true, <=> is 0).

Verified 2026-06-16: Zend PHP 8.2 vs php bin/vm.php.

php-src reference

• php/php-src Zend/zend_enum.c — zend_compare_enums, zend_enum_object_handlers.compare
• php/php-src Zend/zend_operators.c — compare dispatch for IS_ENUM

Repro

test/repro/maintainer_gap_enum_identity_comparison.php:

<?php
enum E: int { case A = 1; case B = 2; }
var_export(E::A < E::B); echo "\n";
var_export(E::A == E::B); echo "\n";
var_export(E::A === E::B); echo "\n";
var_export(E::A <=> E::B); echo "\n";

php bin/vm.php test/repro/maintainer_gap_enum_identity_comparison.php

Zend PHP 8.2:

false
false
false
1

VM today:

true
true
true
0

Scope

• VM compare operators when operands are enum cases — identity for ==/===, backing compare for </<=/<=> only when cases differ
• Depends on enum case object representation (Fix base_convert() enum case operands — TypeError parity (#8976) #9004); fix compare even if scalars still leak elsewhere

Done when (php-src-strict)

• Repro matches Zend output on VM
• Compliance PHPT: same-case === true, different-case === false, <=> by backing
• switch (E::A) { case E::B: ... } does not match incorrectly

[PurHur]

Depends on enum case object identity from #9008 for full parity.

[PurHur]

claim: worker-lane-a — starting this run

[PurHur]

Already fixed on master — VM matches Zend for enum case identity comparison.

Verification:

php bin/vm.php test/repro/maintainer_gap_enum_identity_comparison.php
# false / false / false / 1

php vendor/bin/phpunit --filter "enum_relational_operators|enum_compare_backing_scalar|enum_spaceship|switch_unit_enum"
# OK (9 tests)

Closing as duplicate of prior enum compare work (#4554, #5798, #8897).