Language: enum methods and non-const enum body elements (self-host subset) #2299

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

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)