Regression: backed enum case loose == with backing scalar returns true (re-#5798, zend_operators.c)

[PurHur]

Category

language | php-src-strict

Problem

Identity and loose equality between a backed enum case object and its backing scalar must be false in PHP 8.1+:

enum E: int { case A = 1; }
var_export(E::A == 1);  // false
var_export(E::A === 1); // false

This compiler returns true for == (and historically === too). Closed #5798 fixed this; == regressed.

Root cause likely overlaps #8746 (enum cases materialized as backing scalars in some paths) — fix compare semantics regardless of storage representation.

php-src reference

• php/php-src Zend/zend_operators.c — compare_function enum-case branches
• php/php-src Zend/zend_enum.c — zend_compare_enum_cases

Repro

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php -r "enum E: int { case A=1; } var_export(E::A==1); echo \"\n\"; var_export(E::A===1); echo \"\n\";"
php bin/vm.php -r "enum E: int { case A=1; } var_export(E::A==1); echo \"\n\"; var_export(E::A===1); echo \"\n\";"
'

Engine	==	===
Zend	false	false
VM today	true ❌	verify (should be false)

Also breaks switch (1) { case E::A: … } — tracked in new issue filed this run (switch scalar regression).

Scope (PHP-in-PHP)

Piece	Path
VM compare	lib/VM/Variable.php — equals / compare for TYPE_ENUM_CASE vs int/string
Enum materialization	lib/VM/EnumCaseSupport.php — ensure fetches upgrade to enum objects before compare
JIT/AOT	compare lowering in lib/JIT/Builtin/Type/
Tests	test/compliance/cases/language/enum_case_not_equal_backing_scalar.phpt

Done when

• Repro: both == and === print false on VM
• String-backed enum: E::A == "x" is false
• JIT/AOT agree when compare is lowered
• ./script/ci-fast.sh --filter enum_case_not_equal_backing green

Links

#5798 (closed) · #8746 · #1492

[PurHur]

claim: worker-lane-a — starting this run

[PurHur]

Merged via #8791.

Root cause: VM compare semantics were already correct (Variable::equals / identicalTo reject enum case vs backing scalar). The regression surfaced in compiler call-arg codegen: inline expressions like var_export(E::A === 1, true) wired TYPE_ARG_SEND to a bare CLASS_CONST_FETCH slot instead of the BinaryOp result.

Fix: lib/Compiler.php — treat hoisted BinaryOp/ConstFetch as inline producers, prefer producer slots over runtime enum fetch injection for compare operands, stop producer walks at Array_ boundaries.

Verification:

./script/docker-exec.sh -- bash -lc 'php vendor/bin/phpunit --filter enum_compare_backing_scalar'
./script/docker-exec.sh -- bash -lc 'php vendor/bin/phpunit --filter VmEnumCompareBackingScalarRegressionTest'

Both green (4 tests total).