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feat(ts): type a function value's () result as undefined - #303
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Quest-Claim: f38be08b6246ac3b
A closure, fn pointer, dyn Fn, or function item used as a value returns undefined for (), so a Vec<()> collected from one type-checks. A function item read back from a generic's parameter names the function. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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# Conflicts: # ts/fixtures/lang/expected/durations.ts # ts/fixtures/lang/expected/harness.ts # ts/fixtures/lang/expected/nested.ts # ts/fixtures/lang/expected/orders.ts # ts/fixtures/lang/expected/statics.ts # ts/fixtures/task/expected/drops/iters.ts
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Automated review by review (OpenAI)
Reviewed commit: cdb2189
No actionable bugs found. The direction is sound: function-value signatures consistently represent () as undefined, while declared functions and trait-object methods retain void. Casting named unit-returning functions preserves identity without allocating wrappers; the fallback arrow correctly discards a unit call's result. Recovering FnDef locals is a small, relevant fix, and the added fixture covers function items, pointers, generic callbacks, dynamic calls, and unit-bearing containers. The migration note documents the TypeScript caller impact.
Verification limits: static review of the lowering changes, relevant surrounding code, fixture source, and generated snapshot diffs only. I did not run the translator, TypeScript checks, or differential tests; the PR's reported test results were not independently reproduced.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…s done Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Problem
A function value returning
()was typed=> void, so TypeScript inferredvoidfor what it yields.tscthen refused theundefinedthe output annotates()with. Reproduced:data.iter().map(|_| ()).collect::<Vec<()>>()failed withnested.ts(661,2): Type 'void[]' is not assignable to type 'undefined[]', andVecDeque<()>failed withType 'Iter<void>' is not assignable to type 'Iter<undefined>'.The quest's plan (retype only a closure's return) doesn't cover every case. The same
voidalso leaks through:fnpointer, such asdata.iter().copied().map(f)withf: fn(u8);each<T>(f: impl Fn(u8) -> T)atT = ();dyn Fn;.map(ignore), which is declared: void.Auditing that last case turned up a pre-existing bug: a function item read back from a generic's parameter lowered to
undefined.each(data, half)becamert.iterMap(..., undefined)for any return type, andtscrefused it.Approach
fn_ty(closure,fnpointer,FnDef, anddyn Fntypes) and closure arrows type a()result asundefined.fn_valuecasts a declared function that returns()to that type, as inignore as (a0: rt.u8) => undefined. The arrow fallback calls it withoutreturn.: void. So do the member types of a trait object, whose methods are declared functions.local_exprreads aFnDeflocal asfn_valuerather thanundefined.nestedgains aunitscase:Vec<()>,VecDeque<()>,Option<()>,Result<(), E>, andResult<T, ()>from closures. It also covers afnpointer, a function item, a generic atT = ()given a closure and a function item, adyn Fn, and a method returning an associated type= (). It runs differentially against native wasm32.Snapshots: 47 files changed, all derived from this change. I checked this with a script that maps
=> undefined/): undefined =>back tovoidand strips the new casts; afterwards only these differences remain:fn_valuearrow that no longerreturns a unit call (bounds.ts);Impact
fnpointer,dyn Fn, or function item used as a value returnsundefinedfor()instead ofvoid. This breaks a TS caller passing avoid-typed function, so there is aMIGRATE.mdentry.ts/README.md's type table gains a row.undefined.Alternatives
()returnundefined, declared functions included. That needs no casts and deletesret_ty's special case, but it churns roughly 770 signatures in 157 snapshot files. Rejected per the quest plan.fnpointer identity.Choices made without asking
T = ()hits it.voidon trait objects' member types.Follow-ups
{:?}of anyVecDequeis refused.filter(|u| **u == ())folds totrueand leavesuunread (TS6133).Review
gpt-6.1-sol, medium effort, round 1, on headcdb2189138d3482c8c92555576e38729da53d184againstorigin/main: 0 findings.just cipassed (158 tests), andjust ts moqtranslates and type-checks moq at the pin.Merge of main at
82fb1fc8(#294, #299) intocdb21891, then60cfcefe: took main's generated snapshots and regenerated them (the one interaction is this PR's=> undefinedcast now applied to #299's boundhash$Hashpassed tort.hashing), and repointed #294's newts-zero-sizedquest from the deletedts-unit-closureslink to this PR. Recorded skip, too trivial to review;just cipassed on60cfcefe.🤖 Generated with Claude Code
(written by Claude Opus 5.5)