Language: late static binding (static::method())

[PurHur]

Summary

Resolve static:: to the called class (late static binding) in inheritance hierarchies — including return-value chains where static::foo() propagates through nested calls.

Context

• docs/unsupported-syntax.md and docs/capabilities-syntax.md list LSB as partial.
• Wave 2 tracker Language features wave 2: JIT/syntax gaps tracker (#1222–#1235) #1238 — only Language: late static binding (static::method()) #1231 remains open in the Language: foreach by-reference ($k => &$v) #1222–Language: ??= null coalescing assignment #1235 batch.
• North Star 2 self-host: 🔄 North Star 2: Compiler fully compiles itself (living tracker) #1056, Language: parent:: and static:: resolution in extends chain (#101 phase 1b) #1858 (parent:: / static:: static dispatch).
• PR Language: parent:: static dispatch + return-call slot reuse (#1858) #1873 (DIRTY): VM compliance for parent:: may land separately; return chain through static:: still fails on master.

Problem

class Base { public static function id(): string { return 'base'; } }
class Child extends Base {
    public static function chain(): string {
        return static::id();  // must be 'child' when called as Child::chain()
    }
}

Today: VM may resolve static:: at compile time to the declaring class, or JIT skips with stub policy.

Implementation hints

Layer	Files	Notes
Compiler	lib/Compiler.php	Class_::SCOPE_STATIC on StaticCall — bind called class from runtime receiver
VM	lib/VM.php	resolveStaticCall($calledClass, $method) using get_called_class() semantics
CFG	php-cfg	Ensure static:: in return position does not constant-fold to declaring class
JIT	lib/JIT.php, lib/JIT/Builtin/	SelfHostBuiltinPolicy — stub or deopt until VM green
Tests	test/compliance/cases/language/late_static_binding*.phpt	chain + static::class (#740 ✅ closed)
Self-host	test/selfhost/	Add fixture if spine hits LSB in lib/

Search before coding

rg 'SCOPE_STATIC|LateStatic|static::' lib/Compiler.php lib/VM.php test/
rg 'late_static_binding' test/compliance/

Unblock order

VM called-class resolution (#1231) → JIT lowering → #1858 parent:: parity → self-host spine units

Acceptance criteria

• Child::chain() returns 'child' in VM (./script/ci-fast.sh --filter LateStatic)
• Nested return static::…() in web-safe fixtures passes compliance PHPT
• JIT: explicit stub policy documented OR green on @group llvm subset
• php script/capability-syntax.php row updated
• Language features wave 2: JIT/syntax gaps tracker (#1222–#1235) #1238 table row marked ✅ when done

Verification (local / Docker only)

./script/ci-fast.sh --filter LateStatic
docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  ./script/ci-fast.sh --filter LateStatic

No GitHub Actions.

Dependencies

• Compiler: Class inheritance (extends) and interfaces #101 — extends / inheritance (Language: parent:: and static:: resolution in extends chain (#101 phase 1b) #1858 phase 1b)
• Language: parent:: and static:: resolution in extends chain (#101 phase 1b) #1858 — parent:: static dispatch (parallel)
• Language: Class methods and property access in JIT #58 — OOP method tables
• Language: static::class and ClassName::class constant expressions #740 ✅ — static::class (do not conflate)

Links

• Language features wave 2: JIT/syntax gaps tracker (#1222–#1235) #1238 wave 2 umbrella
• Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492 self-host epic
• ROADMAP 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 Phase 1 Language