fix(transform): #5868 — switch inside async/generator state machines miscompiled

CHANGELOG.md

@@ -1,3 +1,7 @@
+## v0.5.1217 — switch inside async/generator state machines miscompiled (#5885, fixes #5868)
+
+Two state-machine defects, one shared fix. (1) A `yield`/`await` inside a switch case was silently lowered to `0`: the linearizer had no `Stmt::Switch` arm, so the switch fell to the catch-all, was emitted unsplit inside one state, and codegen's fallback lowered the residual `Expr::Yield` to `0.0` — `async f(x){ switch(x){ case 1: return await g() } }` resolved to `0` without suspending, and a generator `yield` inside a case vanished. (2) A loop-level `continue` inside a yield-free switch in a CPS'd loop survived as a raw `Stmt::Continue` the dispatch loop ignored, silently running the rest of the iteration. Both live in production paths since #5854 put async class methods through CPS; minifiers turn if-chains into switches routinely. New `desugar_switch_to_ifs` (generator/break_continue.rs): discriminant temp + match-index + guarded-`if` chain preserving JS switch semantics (single-eval discriminant, in-order first-match-wins tests, fallthrough, default-in-the-middle, `break` — incl. from nested if/try — via done-flag with remainder guarding; `continue`/`return`/`throw` pass through). Wired into a new yielding-switch `linearize_body` arm, a splice in `rewrite_break_continue_in_stmts` for continue-bearing yield-free switches (`next_local_id` threaded through), and the labeled arm (`break label` → plain break in a labeled switch). e2e: `crates/perry/tests/issue_5868_switch_state_machine.rs` (9 scenarios vs node). Note: this PR's labeled run showed parity/smokes/doc-tests failing to BUILD with the pre-existing #5466 E0308 feature-combo breakage (#5872) — zero parity tests executed; compiler-output-regression and the full cargo-test suite are green.
+
 ## v0.5.1216 — promise reactions must not clobber the single handler slot (#5867)
 
 A promise carries one inline reaction slot (`on_fulfilled`/`on_rejected`/`next`); `js_promise_then` diverted 2nd+ reactions to the overflow table, but two other attach paths stored unconditionally: `js_promise_attach_handlers` (Promise.all/allSettled/race/any via `promise_resolve_for_combinator`, stream adapters) destroyed any earlier reaction — `p.then(cb); Promise.all([p])` lost `cb`, and two combinators sharing one pending input destroyed each other's forwarder so the loser's remaining-count never reached zero (permanent hang; the shared webpack/Turbopack chunk-promise shape, #5437 family) — and `js_promise_finally` on a PENDING promise overwrote the slot and nulled `promise.next`. All three occupancy checks (including `js_promise_then` itself) now treat a non-null `next` as occupied too: a degenerate no-arg `p.then()` parks with both closures null and only `next` set, and the spec combinators attach per-element reactions through `js_promise_then` via `invoke_then`, so `const c = p.then(); Promise.all([p])` stranded `c`'s chain. Also carries the #5437-branch fix: `.finally()` on a SETTLED promise dispatches its own wrapper exactly once via `Task::Inline` (previously N settled finallys ran the last wrapper N times — Turbopack `loadChunkAsync` / Next.js CacheSignal), and settled `.finally` now captures the attach-time async context. e2e: `crates/perry/tests/promise_reaction_slot_overflow.rs` (7 scenarios byte-for-byte vs `node --experimental-strip-types`). `promise/then.rs` (2008 lines) is allowlisted 8-over the file-size gate; the topical split of its #1545 value-read-thunk tail is a tracked follow-up.

CLAUDE.md

@@ -8,7 +8,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 Perry is a native TypeScript compiler written in Rust that compiles TypeScript source code directly to native executables. It uses SWC for TypeScript parsing and LLVM for code generation.
 
-**Current Version:** 0.5.1216
+**Current Version:** 0.5.1217
 
 
 ## TypeScript Parity Status