Regression: duplicate backed enum values — first-use Error missing (re-#9193, Zend/zend_enum.c)

[PurHur]

Category

language · php-src-strict

Problem

Closed #9193 added duplicate backing-value detection, but VM regressed: accessing E::A on an enum with duplicate backing values emits property-read warnings on int instead of Zend's first-use Error: Duplicate value in enum E for cases A and B.

Compliance guard test/compliance/cases/language/enum_duplicate_backing_value.phpt is red (verified 2026-06-18).

php-src reference

• php/php-src Zend/zend_enum.c — zend_enum_duplicate_backing_value, lazy case initialization

Repro

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

try {
    echo E::A->name, "\n";
} catch (Throwable $e) {
    echo get_class($e), ': ', $e->getMessage(), "\n";
}

enum F: int { case A = 1; case B = 2; }
echo F::A->name, "\n";

Save as test/repro/maintainer_enum_duplicate_backing.php.

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

Runtime	First block	Second enum
Zend	Error: Duplicate value in enum E for cases A and B	A
VM today	Warning: Attempt to read property "name" on int	may also warn

Root cause overlaps #9676 (enum cases scalarized) — fix duplicate check on enum case objects, not ints.

Scope (this repo)

Layer	Path
VM	lib/VM/BackedEnum.php — duplicate map at first case materialization
Compiler	enum case table build — optional compile-time duplicate detect
Tests	test/compliance/cases/language/enum_duplicate_backing_value.phpt

Done when

• Repro first try prints exact Zend Error: message (class + text)
• Valid enum F::A still prints A
• No E_WARNING property-read noise before the Error
• ./script/ci-fast.sh --filter enum_duplicate_backing green

Verification

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

Related

• Regression: duplicate backed enum values — first-use Error still missing (Zend/zend_enum.c, re-#8876) #9193 / Regression: duplicate backed enum values — no Error at first use (zend_enum.c, re-#5773) #8876 (closed) · Regression: backed enum E::Case yields backing scalars not enum objects (re-#9111, Zend/zend_enum.c) #9676 · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: worker-lane-c — starting this run

[PurHur]

Verification on current master: repro + enum_duplicate_backing_value.phpt + JIT path all green (fixed by #9259 / EnumBackedCaseCheck). No additional code change required — pivoting worker to #9662.

[PurHur]

Architect run 2026-06-19 — worse regression observed

Minimal repro now runs past enum declaration and prints should not run (no Error on first E::A access):

<?php
enum E: int { case A = 1; case B = 1; }
echo "should not run\n";

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

Runtime	Result
Zend	compile-time Error (duplicate backing value)
VM	prints should not run (exit 0)

Done-when should require compile-time fatal when possible (php-src rejects duplicate at declare), not only lazy first-access Error.

[PurHur]

claim: cursor-agent-lane-c — starting this run (compile-time duplicate backing check)

[PurHur]

Merged via #9916.

Fix: EnumBackedCaseCheck::validate() now rejects compile-time duplicate int/string backing values (php-src zend_enum.c parity).

Verification:

php bin/vm.php test/repro/enum_duplicate_value_echo.php  # Fatal, exit 255
vendor/bin/phpunit test/unit/EnumBackedCaseCheckTest.php  # OK (9 tests)
vendor/bin/phpunit test/compliance/EnumVMTest.php --filter enum_duplicate_backing  # OK (3 tests)
vendor/bin/phpunit test/compliance/DuplicateEnumBackingJITTest.php  # OK (1 test)