Language: Enum::tryFrom()/from() — valid backing values return NULL / ValueError (Zend/zend_enum.c)

[PurHur]

Category

language · php-src-strict

Problem

Backed enum static factories Enum::tryFrom() and Enum::from() do not resolve valid backing scalars. Zend returns the matching enum case object (or null / ValueError for invalid input). This compiler returns null for every tryFrom() call and raises ValueError on valid from() input.

This breaks deserialization, config parsing, and any code using tryFrom/from for string/int backed enums.

php-src reference

• php/php-src Zend/zend_enum.c — zend_enum_from(), zend_enum_from_base, case table lookup by backing value
• php/php-src Zend/zend_enum.h — backed enum case hash
• Stubs: php/php-src Zend/Enum.stub.php

Repro (verified 2026-06-18)

<?php
enum E: string {
    case A = 'a';
}

var_dump(E::tryFrom('b')); // Zend: NULL
var_dump(E::tryFrom('a')); // Zend: enum(E::A)

try {
    E::from('a');
    echo "from ok\n";
} catch (ValueError $e) {
    echo 'from fail: ', $e->getMessage(), "\n";
}

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

Call	Zend PHP 8.2	bin/vm.php (today)
E::tryFrom('a')	enum(E::A)	NULL ❌
E::tryFrom('b')	NULL	NULL
E::from('a')	enum(E::A)	ValueError ❌

Int-backed enums show the same pattern (E::tryFrom(1) → NULL).

Scope (this repo)

Layer	Path	Notes
VM	lib/VM/EnumFromHandler.php, enum case tables on ClassEntry	Backing-value → case object lookup
Compiler	lib/Compiler.php enum emission	Ensure case table keys match runtime lookup
JIT/AOT	enum static call lowering	Same semantics as VM when in scope
Tests	test/compliance/cases/language/enum_try_from.phpt, enum_from.phpt

PHP-in-PHP first: lookup logic in lib/VM/ PHP; no new C runtime.

Done when

• tryFrom() returns the enum case object for valid backing values and null for invalid (string + int backed)
• from() returns the case object or throws ValueError with Zend-shaped message for invalid values
• ./script/ci-fast.sh --filter enum_try_from green on VM (JIT when enum static calls are wired)
• Related enum preservation issues (Language: enum case value ::class must return enum name — VM TypeError on backing scalar (Zend/zend_enum.c) #9518, Language: (object) cast on enum case must return same enum case — not empty stdClass (Zend/zend_operators.c) #9569, Regression: serialize()/unserialize() enum cases — backing scalars not E: wire format (re-#6131, var.c) #8723) remain tracked separately

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter enum_try_from'

Related

• North star Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492 · enum preservation batch Parity backlog snapshot 2026-06-17 — enum preservation + php-in-PHP JIT (refs #1492) #9350

[PurHur]

claim: worker-lane-a — starting this run

[PurHur]

Merged via #9613.

Root cause: Primary regression matched #9575 (fixed in #9598 on master). Remaining edge case: BackedEnum::caseForValue() only scanned ClassEntry::$enumCases; when that table was empty/stale, every valid tryFrom()/from() lookup missed and returned null/ValueError.

Fix: Constants-table fallback in lib/VM/BackedEnum.php + live runtime enum resolution in EnumFromHandler.

Verification (Docker):

vendor/bin/phpunit test/unit/VmEnumFromTest.php --filter Issue9603  → OK
vendor/bin/phpunit test/unit/VmEnumCanonicalCaseVariableTest.php --filter testFromResolvesWhenEnumCasesTableEmpty  → OK
vendor/bin/phpunit test/compliance/EnumVMTest.php --filter "enum_try_from|enum_from"  → OK (6 tests)
php bin/vm.php test/repro/issue_9603_enum_from.php  → NULL / enum(E::A) / from ok
php bin/vm.php test/repro/maintainer_enum_from_regression.php  → green