Tracking: untracked TypeScript-feature gaps surfaced by the gap suite

[proggeramlug]

Summary

Three feature gaps surface in the 28-file gap suite (test-files/test_gap_*.ts) that don't have their own tracking issues. Each is a documented standard-library or language feature that perry currently produces wrong/missing output for, but none are crashes — they're scope items for "what to implement next."

The two crash bugs (#447 nested-async hang, #448 *[Symbol.iterator]() class hang) and the two correctness bugs (#449 new.target NaN, #450 Object.defineProperty accessor this-binding) are filed separately — this issue covers the remaining feature gaps.

Gap 1 — Array.fromAsync

console.log(await Array.fromAsync([1, 2, 3]));                        // node: [ 1, 2, 3 ]
console.log(await Array.fromAsync([Promise.resolve(10), …]));         // node: [ 10, 20, 30 ]

Perry: silently emits no output for these two lines. Array.from works; only the fromAsync ES2024 variant is missing.

Gap 2 — Proxy / Reflect handlers not invoked

const target = { name: "obj" };
const proxy = new Proxy(target, {
  get(t, k) { console.log("intercepted get:", k); return t[k]; },
  set(t, k, v) { console.log("intercepted set:", k, "=", v); t[k] = v; return true; },
});
proxy.greeting = "hello";   // perry: silent. node: prints "intercepted set: greeting = hello"
proxy.count = 42;            // ditto

Perry: passes through to the target with no handler dispatch. Reflect.has, Reflect.apply similarly inert. (Surfaced by test_gap_proxy_reflect.ts.)

Gap 3 — JSON.stringify ordering / replacer + reviver edge cases

The first 23 lines of test_gap_json_advanced.ts already diverge from node: perry emits two extra lines ({"name":"Bob","city":"NYC"} and 42) before reaching node's expected output. Likely a replacer/reviver semantics drift. The same file then SIGSEGVs (#451) which masks downstream correctness work — fix #451 first, then re-diff this section.

Suggested approach

These are scope items, not regressions, so they don't block any release. Convert each to its own issue when scheduling, or close this once all three are individually tracked.

Surface coverage

Even with these three gaps filed, the gap-suite top-line is not "27/28 passing" as CLAUDE.md currently claims (that figure is from v0.5.388, ~115 patch versions ago). Current state with parity-runner-style normalization is closer to ~22/28 — 2 hangs (#447, #448), 2 correctness bugs (#449, #450), 1 SIGSEGV (#451), and the three gaps above. Documentation cleanup tracked separately.

[proggeramlug]

Update after v0.5.508 ABI fix landed: re-ran each of the three feature gaps to see what's still broken vs what was masked by the broader bugs.

Array.fromAsync — already works. The original gap-test diff showing it as missing was misleading: test_gap_array_methods.ts's lines 58–59 (Array.fromAsync([1,2,3])) execute before but didn't display because of the async/iter machinery breakage from #447 / #448. Tested in isolation:

const a = await Array.fromAsync([1, 2, 3]);
console.log(a);                                                    // [ 1, 2, 3 ]
const b = await Array.fromAsync([Promise.resolve(10), Promise.resolve(20), Promise.resolve(30)]);
console.log(b);                                                    // [ 10, 20, 30 ]

Perry matches node byte-for-byte. The runtime helper at crates/perry-runtime/src/promise.rs:636 (js_array_from_async) was already complete; codegen routes through it at crates/perry-codegen/src/lower_call.rs:2065. test_gap_array_methods.ts now passes the full suite (no diff against node).

Proxy/Reflect — still requires implementation. Handler dispatch infrastructure not present. Out of scope for this batch.

JSON.stringify ordering drift — the JSON.stringify divergence from #451's bisection (perry emits 2 extra lines in the first 23 of test_gap_json_advanced.ts) was the same ABI bug. Now that #451 is closed, test_gap_json_advanced.ts matches node byte-for-byte (verified post-v0.5.508).

Net result: 2 of the 3 "gaps" in #452 were actually masked by the ABI bug fixed in v0.5.508. Only Proxy/Reflect handler dispatch remains as genuinely unimplemented work; the other two were false alarms surfaced by the v0.5.503 release-readiness audit when the underlying ABI bug truncated test output prematurely. Closing this and filing a separate issue for Proxy/Reflect if/when needed makes sense — it's clearly scope-level work, not a regression.

[proggeramlug]

Closing — 2 of the 3 listed feature gaps (Array.fromAsync + JSON.stringify ordering) turned out to be downstream symptoms of the v0.5.508 ABI bug, both verified working post-fix. Only Proxy/Reflect remains as genuine implementation work; that's scope-level enough to warrant its own issue when prioritized.