Language: enum methods and non-const enum body elements (self-host subset)

[PurHur]

Problem

Backed enum declarations are green (#1356 ✅) for const-like cases, but lib/Compiler.php::compileEnumBody() still throws on any enum body child that is not Op\Terminal\Const_:

throw new \LogicException('Unsupported enum body element: '.get_class($child));

docs/bootstrap-inventory.md may list Unsupported enum body element: when inventory regresses. Host/vendor PHP 8.2+ code uses enum methods, implements clauses, and non-const patterns that block self-host batches.

Goal (v1 subset)

Support the smallest set needed to reduce inventory noise without full PHP 8.1 enum semantics:

1. Enum methods — public function label(): string lowered like class methods (Language: Class methods and property access in JIT #58 / Language: Visibility, constructors, and destructors #145 dependency)
2. Enum interfaces — enum Foo: string implements Bar recorded in class metadata (no dynamic dispatch v1)
3. Document out of scope: pure enums without backing type, enum hooks, const + method combos requiring traits (Language: Traits, abstract classes, and interfaces #144)

Implementation hints

Layer	Path	Notes
Compiler	lib/Compiler.php — compileEnum, compileEnumBody	Accept ClassMethod in enum body; reuse compileClassBody pieces
VM	lib/VM.php	Enum case objects + method dispatch (mirror class vtable v1)
JIT	lib/JIT.php	Defer until VM green; pair #2114 if try/catch in enum method
Lint	lib/Lint/UnsupportedRegistry.php	Remove enum-method kinds when implemented
AOT	lib/AOT/	Same lowering as instance methods after #58

Suggested PR slices

1. Metadata only — parse implements on enum; no dispatch
2. Single enum method — public function name(): string with $this as case wrapper
3. Compliance — test/compliance/cases/enum_method.phpt
4. Inventory — regen docs/bootstrap-inventory.md; expect warning delta

Test plan

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter Enum'
php bin/vm.php -r 'enum E: string { case A = "a"; public function x(): string { return $this->name; } } echo E::A->x();'

Acceptance criteria

• compileEnumBody accepts at least one ClassMethod without throw
• Compliance PHPT passes on VM (JIT optional follow-up)
• php script/bootstrap-inventory.php --check still clean or documented delta
• script/capability-matrix.php row updated

Verification (local / Docker only)

./script/ci-fast.sh --filter enum
make test-harness   # pre-merge when JIT touched

No GitHub Actions (#394 ✅).

Dependencies

• Language: Class methods and property access in JIT #58 — instance method lowering (shared machinery)
• Language: Visibility, constructors, and destructors #145 — visibility (defer private enum methods to v2)
• Language: Enum declarations (enum / backed enum) #1356 ✅ — backed enum cases
• Self-host: CFG lowering batch coordination (stmt/expr/op trackers) #2362 — coordinate with expr/op batches if enum bodies pull new operands
• Blocks: self-host files using enum methods in lib/ (discover via bootstrap-inventory-triage.php after Language: Class methods and property access in JIT #58)

Links

• ROADMAP 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 Phase 1 Language · Wave 3 close-out Docs: wave3 umbrella #1380 close-out — 12/12 language + 13/13 stdlib on master #1939
• Parent coordination: Self-host: CFG lowering batch coordination (stmt/expr/op trackers) #2362 (CFG batch tracker)

[PurHur]

Implementation expansion (backlog pass)

Compiler paths

Symbol	Location	Change
compileEnumBody	lib/Compiler.php	Accept Op\Stmt\ClassMethod alongside Const_
compileEnum	same	Record implements list on enum metadata (no dispatch v1)
Enum case values	existing #1356 ✅	Unchanged

Reuse compileClassMethod() helper where possible — enums share VM class registry with TYPE_ENUM (verify constant in OpCode).

VM / JIT ordering

1. VM: register enum methods on enum id; calls via MethodCall on enum case or enum name per PHPT design.
2. JIT: blocked on Language: Class methods and property access in JIT #58 for ClassMethod emission — document markTestSkipped in @group llvm PHPT until then.
3. AOT: same as class methods once VM green.

First PR slice

// test/compliance/cases/enum_method.phpt
enum Status: string {
    case Ok = 'ok';
    public function label(): string { return $this->name; }
}

Assert Status::Ok->label() or static call pattern you support in v1.

Inventory probe

php script/bootstrap-inventory-triage.php --grep 'Unsupported enum body' --top 5
php script/bootstrap-inventory.php | grep -c 'Unsupported enum body element'

Docs

• Extend docs/capabilities-syntax.md enum row (parent Language: Enum declarations (enum / backed enum) #1356).
• script/capability-syntax.php if row is generated.

Dependencies (strict)

Land after or with minimal #58 VM method dispatch — otherwise PHPT passes parse/lowering but fails at runtime.

Epic #1492 · ROADMAP #78 Phase 1.