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es-get-iterator broken by IIFE now allowing contextual return type #45559
Description
Broken by #45007:
interface Iterable<T, TReturn = unknown, TNext = undefined> {
[Symbol.iterator](): Iterator<T, TReturn, TNext>;
}
type InferIterable<T> = T extends Iterable<infer TYield, infer TReturn, infer TNext>
? Iterator<TYield, TReturn, TNext>
: unknown extends T
? Iterator<unknown> | undefined
: undefined;
declare function getIterator<T>(iterable: T): InferIterable<T>;
var x = getIterator((function*() { yield "foo"; yield "bar"; })());Expected: x: Iterator<"foo" | "bar", void, unknown>
Actual: x: Iterator<"foo" | "bar", void, any>
I think this is an acceptable break, but I want another round of thinking about it now that we have a concrete example.
Activity
sandersn commentedon Aug 24, 2021
Daniel Rosenwasser (@DanielRosenwasser) you probably want to know about this too.
sandersn commentedon Oct 5, 2021
Smaller repro:
sandersn commentedon Oct 6, 2021
This is an inconsistency in our iterator checking; with no contextual type, the hard-coded TNext default is
unknown; with a defective,next-free contextual type, the hard-coded default isanyinstead.We should maybe consider fixing this, but only if it doesn't break anybody, or if anybody thinks the current state is bad enough.
In any case, I think this change is fine to ship as-is.