[kixelated]

Problem

rust2-ts refused AssertUnwindSafe outright (found by #528): it couldn't be made, so it couldn't wrap a future or a closure either. The rest of std::panic was refused as unsupported calls: catch_unwind, resume_unwind, panic_any, Location, set_hook, and take_hook, and Debug of a dyn Any, which catch_unwind(..).unwrap() needs. No moq consumer calls these; the maintainer plans all of std.

Approach

Panics abort, on wasm32's panic=abort and in the translation alike, so most of std::panic has an exact translation:

• AssertUnwindSafe<T> is what it holds, as Reverse<T> is, and JS erases it as it does a Box or Pin where a write in place checks what JS keeps: made, its field read and written, Deref/DerefMut, Default, From, Debug (AssertUnwindSafe(..), as std's derived-style tuple), drops, a call through its FnOnce, and a poll through its Future, each forwarding to what it holds.
• catch_unwind(f) is Ok(f()): a panic inside throws on, as native aborts after the hook.
• resume_unwind throws rt.Abort, as native aborts without running the hook.
• panic_any(p) panics with p if it is a &str or String, and with Box<dyn Any> otherwise, as std's hook writes it. Edition-2015 begin_panic had the same bug (any payload was its JS string) and shares the fix.
• Debug of a dyn Any writes Any { .. }.

What can't match yet stays refused with a span and a reason: Location (it needs each #[track_caller] function's caller), and set_hook/take_hook (a hook reads each panic's Location, which panics don't carry).

Tests: a new lang/panics differential fixture (673 cases, 97 panics, 31 aborts). It covers AssertUnwindSafe of numbers, a Vec, a struct, nested wrappers, written through *, .0, and &mut *, and an Arc shared with a clone and a Vec<u8> replaced whole through a generic &mut; Debug plain, alternate, padded, and nested; Default and From; drop order moved, replaced, and at scope end; calls of closures, fn items, closures that write captures or own values that drop; catch_unwind of closures, fn items, borrowed closures, wrapped closures, a Box<dyn FnOnce>, and one that panics; futures polled by hand and awaited, nested, and dropped unpolled; panic_any of each payload kind and resume_unwind. Mutating resumeUnwind to a plain panic and the Box<dyn Any> text gives 72 differences. The reject fixture gains Location::caller and the hooks.

Impact

• Public API: the translator's output. New runtime export: rt.resumeUnwind. No breaking change.

Alternatives

• Lowering AssertUnwindSafe's impls from core's MIR: its Future uses Pin::map_unchecked_mut, and a class per wrapper would allocate for a marker. Erasing it, as Reverse is, needs no runtime.
• Translating Location::caller here: it needs a hidden location parameter on every #[track_caller] function and refusals for indirect calls, a change of its own (quest below).

Follow-ups

• A panic's Location (new quest): Location::caller and #[track_caller].
• A panic hook (new quest): set_hook, take_hook, PanicHookInfo; requires the first.

Review

Codex (quest review, gpt-6.1-sol, medium):

• Round 1, head 1d4d13ab: "Unwrap AssertUnwindSafe in representation-sensitive helpers" (replacing an AssertUnwindSafe<Arc<_>> through a &mut wrote into the shared Arc; an AssertUnwindSafe<Vec<u8>> took vecAssign). Fixed in 7394ffcb: Translator::erased peels AssertUnwindSafe. Reproduced first: the Vec case failed tsc and the Arc case alone gave 20 differences.
• Round 2, head 7394ffcbca4f3f45f09f7c2bdeb8c1ca7e78ba2f: no findings. Since then, 6833ceeb and 10b21680 only merge origin/main (feat(ts): translate Rc::as_ptr, Arc::as_ptr, and ptr::addr_eq, and copy what their pointers compare #511, feat(ts): translate vec![x; n] of a value that drops #534, feat(ts): translate lossy and chunked UTF-8 decoding #537, fix(ts): keep a nested Vec's capacity where clone_from writes over it #533, chore(quest): plan matching a Cow<str>'s variant #541), with no conflicts; just ci passes on 10b21680.

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Commits

Reviewing files that changed from the base of the PR and between f0b2a31 and 10b2168.

Files ignored due to path filters: 1

• ts/Cargo.lock is excluded by !**/*.lock

Files selected for processing: 37

• quest/m3/README.md
• quest/m3/ts-panic-hook.md
• quest/m3/ts-panic-location.md
• ts/README.md
• ts/fixtures/lang/panics/Cargo.toml
• ts/fixtures/lang/panics/expected/core/any.Any.ts
• ts/fixtures/lang/panics/expected/core/option.ts
• ts/fixtures/lang/panics/expected/core/result.ts
• ts/fixtures/lang/panics/expected/core/task/poll.ts
• ts/fixtures/lang/panics/expected/harness.ts
• ts/fixtures/lang/panics/expected/lib.ts
• ts/fixtures/lang/panics/expected/panics.Countdown.ts
• ts/fixtures/lang/panics/expected/panics.Logged.ts
• ts/fixtures/lang/panics/expected/panics.Point.ts
• ts/fixtures/lang/panics/expected/panics.ts
• ts/fixtures/lang/panics/src/lib.rs
• ts/fixtures/lang/panics/src/panics.rs
• ts/fixtures/lang/panics/ts.toml
• ts/fixtures/reject/census.txt
• ts/fixtures/reject/expected.txt
• ts/fixtures/reject/src/lib.rs
• ts/fixtures/reject/src/panics.rs
• ts/fixtures/reject/ts.toml
• ts/runtime/rt.ts
• ts/src/census.rs
• ts/src/lower/body.rs
• ts/src/lower/copy.rs
• ts/src/lower/drop.rs
• ts/src/lower/dynamic.rs
• ts/src/lower/fmt.rs
• ts/src/lower/library.rs
• ts/src/lower/mir/call.rs
• ts/src/lower/mir/place.rs
• ts/src/lower/mir/rvalue.rs
• ts/src/lower/mod.rs
• ts/src/lower/task.rs
• ts/tests/fixtures.rs

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