TS Conformance: remaining Fail-bucket clusters (post-#188/#202 survey)

[nickna]

Part of #80. Survey of the 21 Fail + 4 ParseError tests remaining after PRs #201/#203 and the declare-function/extends fixes (PR pending). Clusters by root cause:

Fixed in the pending PR (tests improved, not yet flipped)

• declare function never registered (TS2304 extras on 4+ tests)
• interface B extends A<Base> rejected with TS2312
• interface I extends SomeClass rejected with TS2312

Remaining clusters

1. Overload resolution subtype pass — anyAssignabilityInInheritance (16 extras): foo(a) with a: any must pick the (x: any) overload (tsc's subtype-matching pass runs before the assignability pass; any is not a subtype of number). We pick the first assignable overload → wrong return types cascade into TS2322s.
2. Parameter defaults referencing earlier parameters — genericCallWithObjectTypeArgsAndInitializers: function foo4<T, U extends T>(x: T, y: U = x) → TS2304 on x; earlier params must be in scope for later defaults (then the expected TS2322s emerge naturally).
3. Self-referential typeof/initializers — assignmentCompatWithObjectMembers: var a: { foo: typeof a } and var a2 = { foo: a2 } → TS2304.
4. Member accessibility in structural compat — assignmentCompatWithObjectMembersAccessibility (16 missing TS2322): private/protected members must make otherwise-identical types incompatible (distinct declarations) in the module-scoped cases.
5. Index-signature assignability against generic instantiations in generic context — assignmentCompatWith{Numeric,String}Indexer2 remainders (A<T> vs { [x: number]: Derived } inside function foo<T extends Base>()).
6. Enum assignability details — enumAssignability (6 missing: enum → number-literal-typed positions?), enumAssignabilityInInheritance (extra TS2322@L81, missing TS2403 var-redecl checks).
7. Conditional-type evaluation — conditionalTypes1/2, conditionalTypesExcessProperties, inferTypesWithExtends2 — deep checker work on conditional/infer evaluation.
8. Parser — inferTypes1/2, inferTypesWithExtends1 (Expect ';' after type alias — likely multiline conditional/infer alias syntax), nullAssignedToUndefined (Invalid assignment target at L1).
9. Known blocked: covariantCallbacks (always-on callback rule, TS Conformance: structural variance for generic interface instantiations (covariantCallbacks, genericCallSignatures4) #202), unionTypesAssignability (we emit TS2741 where tsc emits TS2322 at the same lines — diagnostic-code choice), assignmentCompatWithDiscriminatedUnion (10 extras — discriminant narrowing in assignability).

Each cluster is independently attackable; (1), (2), and the TS2741→TS2322 code choice in (9) look like the best effort-to-flip ratios.

[nickna]

PR #227 merged — four clusters from this catalogue are done:

• declare-function registration (cluster: TS2304 extras)
• interface extends generic instantiation
• interface extends class
• overload subtype pass → anyAssignabilityInInheritance flipped Fail → Pass (subset Pass 53 → 54, Fail 21 → 20, 0 regressions)

Remaining clusters from the survey, in ranked order: param defaults referencing earlier params (genericCallWithObjectTypeArgsAndInitializers), TS2741-vs-TS2322 code choice (unionTypesAssignability), self-referential typeof, accessibility modeling, index-sigs vs generic instantiations, enum details, conditional-type evaluation, and the parser gaps.

[nickna]

PR #231 merged — round 2 complete, three more flips:

• param defaults referencing earlier params → genericCallWithObjectTypeArgsAndInitializers ✅
• number-index optionality (named members were never checked against number index signatures; the optional-undefined exemption is string-index-only) → optionalPropertyAssignableToStringIndexSignature ✅
• TS2741/TS2322 code rules — the real tsc mechanism: the missing-property promotion fires only on a type pair's first failure (relation cache reports repeats as plain TS2322), and union sides always report TS2322 → unionTypesAssignability ✅

Subset now Pass 57 / Fail 17 / ParseError 4 (session start: Pass 33 / Fail 41). Remaining clusters per the catalogue: self-referential typeof, accessibility modeling, index-sigs vs generic instantiations, enum details, conditional-type evaluation, parser gaps, and the #202-blocked callback rule.

[nickna]

PR #236 merged — round 3:

• self-referential typeof/initializers → assignmentCompatWithObjectMembers ✅ (namespace var hoisting; the body parser was also dropping IsVar)
• Enum cluster: E.A now types as the enum, numeric literals no longer flow into enums (widened number still does), TS2403 var-redeclaration implemented, and overload resolution now takes the first declared match (tsc semantics) instead of most-specific. Both enum tests narrowed to 2 wrong lines each, blocked solely on lib-type modeling (Object/Date/String resolve to any) — that's TS Conformance Phase 1.5 (deferred): load tsc lib.d.ts files into type checker #99 territory and now the dominant blocker for several remaining tests.

Subset: Pass 58 / Fail 16 / ParseError 4 (session start: Pass 33 / Fail 41). Remaining clusters: lib-type modeling (#99), accessibility, index-sigs vs generic instantiations, conditional types, parser gaps, #202 callback rule.

[nickna]

PR #241 merged — round 4 (the lightweight lib-globals option):

• Object/Date/RegExp/String/Number/Boolean now model honestly in type position (were any); excess-property check skips empty targets; TS2403 implemented through VarHoister (duplicate top-level vars are rewritten to assignments at parse time — the synthesized Expr.Assign now carries IsVarRedeclaration).
• enumAssignability ✅ and enumAssignabilityInInheritance ✅ — the enum cluster is fully closed.

Subset: Pass 60 / Fail 14 / ParseError 4 (session start: Pass 33 / Fail 41). Remaining: conditional types (4), object-member details (~5), accessibility, indexers-vs-generics (2), discriminated union, covariantCallbacks (#202-blocked), and the 4 parser gaps — the parser cluster is the most attractive untouched target.