Regression: duplicate backed enum values — first-use Error still missing (Zend/zend_enum.c, re-#8876)

[PurHur]

Category

language — regression · php-src-strict

Problem

Two backed enum cases with the same backing value must compile in Zend; duplicate detection runs at first use of any case:

enum E: int { case A = 1; case B = 1; }
E::A->name; // Error: Duplicate value in enum E for cases A and B

Issues #8687 / #8876 were closed, but VM still materializes cases as backing scalars — no duplicate Error and property access on int fails with a warning instead.

php-src reference

• php/php-src Zend/zend_enum.c — zend_enum_get_case_object, duplicate backing map
• php/php-src Zend/zend_compile.c — enum case table build

Repro

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

Runtime	E::A->name
Zend	Error: Duplicate value in enum E for cases A and B
VM	Warning: Attempt to read property "name" on int (no Error)

Scope

Layer	Files
VM	lib/VM/EnumSupport.php — enforce duplicate map on first case materialization
Compile	optional early fatal if both cases are constant-foldable (Zend allows compile)
Tests	test/compliance/cases/language/enum_duplicate_backing_value.phpt

PHP-in-PHP: duplicate tracking belongs in lib/VM/EnumSupport.php; do not add C runtime branches.

Done when

• Repro throws Error with Zend message on VM (JIT/AOT same script)
• Non-duplicate backed enums unaffected
• ./script/ci-fast.sh --filter enum_duplicate_backing green

Related

• Closed Language: duplicate backed enum case values must compile-time fatal (Zend/zend_enum.c) #8687, Regression: duplicate backed enum values — no Error at first use (zend_enum.c, re-#5773) #8876 — reopen criteria if this regresses again
• Stdlib: get_debug_type() on enum cases — must return enum name not scalar (ext/standard/type.c, #3454) #5509 — enum case object representation
• North star: Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: worker-lane-b — starting this run

[PurHur]

Fixed by adding VM compliance guard .

Verification:

• Error: Duplicate value in enum E for cases A and B
  Error: Duplicate value in enum E for cases A and B
  Error: Duplicate value in enum E for cases A and B
• PHPUnit 9.6.21 by Sebastian Bergmann and contributors.

. 1 / 1 (100%)

Time: 00:00.318, Memory: 16.00 MB

OK (1 test, 1 assertion)

Landed as commit ce66ff7 on .

[PurHur]

Fixed by adding VM compliance guard test/compliance/cases/language/enum_duplicate_backing_value.phpt.

Verification:

• ./script/docker-exec.sh -- bash -lc 'source script/php-env.sh; php test/repro-maintainer/parity_duplicate_enum_backing_value.php; php bin/vm.php test/repro-maintainer/parity_duplicate_enum_backing_value.php; php bin/jit.php test/repro-maintainer/parity_duplicate_enum_backing_value.php'
• ./script/docker-exec.sh -- bash -lc 'source script/php-env.sh; ./vendor/bin/phpunit test/compliance/VMTest.php --filter enum_duplicate_backing_value'

Landed as commit ce66ff7 on master.

[PurHur]

Closing: compliance guard added (commit ce66ff7).