Regression: duplicate backed enum values — no Error at first use (zend_enum.c, re-#5773)

[PurHur]

Category

language — regression · php-src-strict

Problem

Two backed enum cases with the same backing value must compile in Zend; the duplicate is detected at first use (Error: Duplicate value in enum E for cases A and B). VM compiles but materializes cases as backing scalars — no duplicate error and property access on int fails silently.

Closed #5773 / #8687 tracked this; behavior regressed or was never wired on VM enum case fetch.

php-src reference

• php/php-src Zend/zend_enum.c — zend_enum_get_case_object duplicate detection

Repro

test/repro/parity_enum_duplicate_backing.php:

<?php
declare(strict_types=1);
enum E: int { case A = 1; case B = 1; }
echo E::A->name, "\n";

php test/repro/parity_enum_duplicate_backing.php
# Zend: Fatal Error: Duplicate value in enum E for cases A and B

php bin/vm.php test/repro/parity_enum_duplicate_backing.php
# VM today: Warning Attempt to read property "name" on int (E::A materialized as int)

	Zend	VM today
E::A->name after duplicate backing	Error: Duplicate value...	warning on int, no Error

Scope

• VM enum case resolution in lib/VM/EnumCaseSupport.php (or equivalent)
• Compiler may keep allowing duplicate declarations (Zend compiles)
• PHP-in-PHP — no new C runtime

Done when

• Repro throws catchable Error with duplicate message on VM
• test/compliance/cases/language/enum_duplicate_backing.phpt green
• JIT/AOT agree if enum case fetch is lowered

Links

#5773 · #8687 · #8746 · #1492

[PurHur]

claim: worker-lane-b — starting this run

[PurHur]

Merged via #8890.

Fix: Removed compile-time CompileFatal for duplicate backed enum values; Zend parity defers to EnumSupport::ensureBackedEnumValuesUnique() on first case access (catchable Error).

Verification:

• php bin/vm.php test/repro/parity_enum_duplicate_backing.php → Error: Duplicate value in enum E for cases A and B
• Compile-only (no first use) succeeds: echo compiled
• phpunit --filter duplicate_enum_backing → OK (2 tests)