Language: backed enum arithmetic with int/float must TypeError — E::A + 1 (Zend/zend_operators.c)

[PurHur]

Category

language — php-src-strict enum operators

Problem

Backed enum cases are not silently coerced to their backing scalar for +, -, *, /, %, and related numeric operators. Zend throws TypeError: Unsupported operand types: E + int.

This compiler evaluates E::A + 1 as 2 when E::A backs 1, breaking enum operator parity.

Related but narrower: #8972 (array_reduce accumulator), #9546 (===).

php-src reference

• php/php-src Zend/zend_operators.c — add_function, sub_function, … enum operand guards
• php/php-src Zend/zend_enum.c — enum zval type

Repro (failure today)

Save as test/repro-maintainer/enum_numeric_arithmetic.php:

<?php
declare(strict_types=1);

enum E: int { case A = 1; }

foreach (['+', '-', '*'] as $op) {
    try {
        $expr = 'E::A ' . $op . ' 1';
        echo $expr, '=', eval('return ' . $expr . ';'), "\n";
    } catch (Throwable $e) {
        echo $expr, ' ', get_class($e), "\n";
    }
}

Minimal single-op repro:

<?php
enum E: int { case A = 1; }
try { echo E::A + 1; } catch (Throwable $e) { echo get_class($e), "\n"; }

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

Check	Zend	VM (today)
E::A + 1	TypeError	prints 2 ❌
E::A - 1	TypeError	coerced math ❌
E::A * 2	TypeError	coerced math ❌

Scope (PHP-in-PHP)

Layer	Path
VM	lib/VM/Variable.php binary ops / lib/VM.php opcode handlers — reject enum+scalar before backing coercion
JIT/AOT	lib/JIT/JitValueCompare.php, arithmetic lowering — same guard
Shared	central enum-operand helper (pair with #9546)

Done when

• Repro throws TypeError for +, -, * on VM
• Enum case compare with another enum case unchanged (Regression: enum relational operators — < and <=> order inverted vs Zend (re-#9016, zend_enum.c) #9288)
• test/compliance/cases/language/enum_numeric_arithmetic.phpt green
• No new logic in runtime/*.c

Related

• Language: backed enum strict compare with backing scalar — E::A === 1 must be false (Zend/zend_enum.c) #9546 · Stdlib: array_reduce() — enum case + int arithmetic must TypeError not coerce backing int (ext/standard/array.c) #8972 · Stdlib: strval() on enum cases — must Error not coerce backing scalar (ext/standard/type.c, php-src-strict) #9001 (strval) · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

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

[PurHur]

Merged via #9574

Verification
```bash
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php test/repro-maintainer/enum_numeric_arithmetic.php
php bin/vm.php test/repro-maintainer/enum_numeric_arithmetic.php
php vendor/bin/phpunit --filter "enum_numeric_arithmetic|enum_scalar_arithmetic|enum_pow_mod" test/compliance/'
```

All paths throw TypeError: Unsupported operand types: E + int (and -/*) — no backing-scalar coercion. Primary guards were already in operandsValidForNumericOp / JitEnumNumericOperandGuard (#5790); PR hardens toNumericForArithmetic() and adds #9568 repro + compliance PHPT.