class methods referencing a const declared after the class: capture omitted (ReferenceError) or spurious TDZ at class definition — kills Next.js standalone boot (bundled semver) #6523

Summary

A class whose methods reference a lexical binding (const/let) declared after the class miscompiles. Legal JS — TDZ applies at call time, and the bindings are initialized before any method runs — but perry's class-capture machinery snapshots captures by value at the class's declaration site, so forward bindings break in two ways:

A. Simple function scope — capture omitted entirely:

(function factory(e) {
  const s = Symbol("x");
  class Comparator {
    static get ANY() { return s; }
    constructor(v) { a("dbg", v); this.max = n; }   // a, n declared BELOW
  }
  e.exports = Comparator;
  const a = function () {};
  const n = 16;
  new Comparator("x");   // perry: ReferenceError: a is not defined   node: works
})({ exports: {} });

HIR shows ClassExprFresh { captured_args: [LocalGet(s)] } — a/n are missing from the captures.

B. Module-factory scope with TDZ boxes — spurious TDZ throw at class definition:

next/dist/compiled/semver module 842 (const s = Symbol("SemVer ANY"); class Comparator {...} with the debug fn + sibling requires declared below the class) lowers to PreallocateTdzBoxes([41..46]) + ClassExprFresh { captured_args: [LocalGet(41)..LocalGet(46), LocalGet(47)] }. The captured-arg LocalGet on a TDZ box emits a checked value read (js_box_get_bits → js_throw_reference_error_tdz), so defining the class throws ReferenceError: Cannot access undefined before initialization — at module init, before any user code runs.

Impact

Any bundled/minified package that declares module constants after a class that uses them. Concretely: next/dist/compiled/semver — a Next.js 16 standalone server dies at BOOT (before Ready, 100% deterministic) once module 608/842's init runs. This is the current gscmaster boot blocker (behind the statuses .message bug fixed in #6522).

lldb stack (debug-symbol build, b js_throw_reference_error_tdz):

js_throw_reference_error_tdz ← js_box_get_bits ← …semver_index_js__13 (module 842 factory)
  ← js_native_call_value ← …__167 (__nccwpck_require__) ← …__12 ← …__0 ← init_body ← main

Contrast

Plain closures/arrows capturing the same forward-declared consts work correctly (box-based captures, read at call time). Only the class path (RegisterClassCaptures / ClassExprFresh decl-site snapshot; class_captures.rs "decl-site snapshot" for statics) has this semantics gap. The shared-mutable-capture path (#6497/#6470) already keeps whole box handles for mutated captured locals — but forward-declared immutable bindings either aren't collected (A) or are TDZ boxes read eagerly (B).

Direction

Class captures of not-yet-initialized lexical bindings need the closure treatment: capture the box, read through it at method-call time (mirror __perry_cap_* field reads / static snapshot reads via id[0]), never a checked value read at class-definition time. Case A additionally needs the capture collection to include bindings declared after the class (forward lexical names are already tracked for the TDZ machinery — forward_lexical_names, #6062).

Repros: standalone files above; the full trigger is perry compile of next/dist/compiled/semver/index.js + require driver (dies at init).