Language: property/parameter/static defaults with enum case ->value — compile-time constant folding (zend_compile.c, extends #3803)

[PurHur]

Category

language

Problem

Zend treats E::Case->value (and similar enum-case member fetches) as a compile-time constant for default values of properties, static properties, and parameters. This compiler rejects them with #3803 ("Property/Parameter default must be a compile-time constant") even though the same expression works in const G = E::A->value; at file scope.

Blocks idiomatic PHP 8.1+ defaults that mirror backing values without magic numbers.

php-src reference

• php/php-src Zend/zend_compile.c — zend_compile_default_value(), enum case fetch in constant expressions
• php/php-src Zend/zend_constants.c — ZVAL_LONG / ZVAL_STRING folding from backed enum cases
• php/php-src Zend/zend_enum.c — ->value on enum cases in constant context

Repro (failure today)

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

class C {
    public int $n = E::A->value;           // compile error VM; Zend OK
    public static int $s = E::A->value;    // compile error VM; Zend OK
}
function f(int $n = E::A->value): int { return $n; } // compile error VM; Zend OK
var_dump((new C())->n, C::$s, f());

docker info >/dev/null
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php bin/vm.php test/repro/maintainer_enum_value_property_default.php  # parseAndCompile #3803
php bin/vm.php test/repro/maintainer_static_default_enum_value.php
php bin/vm.php test/repro/maintainer_param_default_enum_value.php
/usr/bin/php test/repro/maintainer_param_default_enum_value.php        # int(1)
'

Form	Zend	VM
const G = E::A->value;	int(1) ✅	int(1) ✅
public int $n = E::A->value	compiles	#3803 fatal
public static int $s = E::A->value	compiles	#3803 fatal
function f($n = E::A->value)	compiles	#3803 fatal

php-src-strict: unit enum cases without ->value remain compile errors; only backed-case ->value (and other Zend-allowed constant exprs) fold.

Scope (this repo)

Layer	Path
Compiler	lib/Compiler.php — extend default-value folder for EnumCaseFetch->value
CFG	constant expression evaluator shared with file-scope const
VM	ensure default slots materialize before instance/static init
Tests	test/compliance/cases/language/enum_case_value_default.phpt

PHP-in-PHP: fold in compiler — no C runtime default tables.

Done when

• All three default forms in repro compile and print int(1) on VM
• Unit enum E { case A; } with ->value default still compile-errors like Zend
• ./script/ci-fast.sh --filter enum_case_value_default green

Related

• Language: non-literal default parameter values — class/global constants and null (Zend zend_compile.c parity) #3803 (closed) — literal/self::/null defaults; this extends enum-case member access
• Language: property defaults with new expression (PHP 8.3) — runtime init fails with null TypeError (zend_compile.c) #7375 — new expression in property defaults (distinct form)

[PurHur]

claim: worker-lane-B — starting this run

[PurHur]

Merged via #7402.

Verification
```bash
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php bin/vm.php test/repro/maintainer_enum_value_property_default.php
php bin/vm.php test/repro/maintainer_static_default_enum_value.php
php bin/vm.php test/repro/maintainer_param_default_enum_value.php
vendor/bin/phpunit --filter enum_case_value_default
'
```
All three repro scripts print int(1); compliance enum_case_value_default.phpt green.

Unit enum case without ->value still compile-errors (object default vs typed parameter).