Regression: BackedEnum::from()/tryFrom() lookup broken — valid backing values NULL / ValueError (re-#3114, Zend/zend_enum.c)

[PurHur]

Category

language | stdlib · php-src-strict · regression vs closed #3114

Problem

BackedEnum::tryFrom() and BackedEnum::from() must resolve a backing scalar to the canonical enum case object (E::A). Audit (2026-06-19): both methods fail for valid backing values — tryFrom(1) returns NULL and from(1) throws ValueError: 1 is not a valid backing value even when E::A = 1 exists.

This blocks enum deserialization, HTTP/query parsing, and any code using tryFrom/from at runtime. Distinct from #9889 (invalid-value error message when lookup path runs).

php-src reference

• php/php-src Zend/zend_enum.c — zend_try_enum_from_case(), zend_enum_from_case(), backed-value hash
• php/php-src Zend/zend_enum.stub.php — BackedEnum::from / tryFrom
• Closed baseline: Language: enum_from() — BackedEnum::from / tryFrom (PHP 8.1) #3114

Repro

test/repro-maintainer/backed_enum_from_tryfrom.php:

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

var_export(E::tryFrom(1));
echo "\n";
var_export(E::from(1));
echo "\n";

enum Color: string { case Red = 'red'; }
var_export(Color::tryFrom('red'));
echo "\n";

Commands

php test/repro-maintainer/backed_enum_from_tryfrom.php
# Zend:
# \E::A
# \E::A
# \Color::Red

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php test/repro-maintainer/backed_enum_from_tryfrom.php'
# VM today:
# NULL
# ValueError: 1 is not a valid backing value for enum E

Call	Zend	VM (today)
E::tryFrom(1)	\E::A	NULL
E::from(1)	\E::A	ValueError
Color::tryFrom('red')	\Color::Red	NULL

Scope (PHP-in-PHP)

Path	Work
lib/VM/BackedEnum.php	caseForValue() / matchCaseForBackingValue() — ensure ClassEntry::$enumCases populated at runtime
lib/VM/EnumFromHandler.php	execute() return path via BackedEnum::canonicalCaseVariable()
lib/VM/EnumSupport.php	Case table / constant fallback (#9603)
Tests	test/compliance/cases/language/backed_enum_from_tryfrom.phpt

No new C in runtime/ — lookup belongs in PHP VM helpers.

Done when (php-src-strict)

• Repro prints three enum case objects on VM matching Zend
• tryFrom(invalid) returns null; from(invalid) throws ValueError with php-src message (Language: BackedEnum::from() invalid value — ValueError not 'Method call on non-object' (Zend/zend_enum.c) #9889)
• Returned case is enum object (not backing scalar) — get_debug_type(E::from(1)) === 'E'
• JIT/AOT: either share VM handler bridge or document VM-only gap in docs/capabilities.md

Related

• Language: enum_from() — BackedEnum::from / tryFrom (PHP 8.1) #3114 (closed) · Language: BackedEnum::from() invalid value — ValueError not 'Method call on non-object' (Zend/zend_enum.c) #9889 · Regression: Enum::cases() / UnitEnum::cases() returns empty array — re-#9682/#5462 (Zend/zend_enum.c) #9876 (cases()) · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

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

[PurHur]

Audit: BackedEnum::from()/tryFrom() repro already green on master (2026-06-21) — php bin/vm.php test/repro-maintainer/backed_enum_from_tryfrom.php prints enum case objects. No code change needed this run; issue can be closed separately.

[PurHur]

Closed by lane-C audit (2026-06-23): BackedEnum::from/tryFrom repro green on master — VM prints \\E::A / \\Color::Red matching Zend.