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TypeScript unexpectedly inferring 'any' type. #30250
Description
Given the following code:
interface Widget { x: number }
declare type Unwrap<T> = T extends Promise<infer U1> ? UnwrapSimple<U1> : UnwrapSimple<T>;
declare type primitive = Function | string | number | boolean | undefined | null;
declare type UnwrapSimple<T> = T extends primitive ? T : T extends Array<infer U> ? UnwrappedArray<U> : T extends object ? UnwrappedObject<T> : never;
export interface UnwrappedArray<T> extends Array<Unwrap<T>> {
}
export declare type UnwrappedObject<T> = {
[P in keyof T]: Unwrap<T[P]>;
};
declare var w: Widget;
declare type TupleType = [Widget, string];
declare var o: UnwrappedObject<TupleType>;TypeScript oddly infers a type of [any, string] for o. This is surprising to us given how we would think these type operators would work. First, given the definition UnwrappedObject i would expect UnwrappedObject<TupleType> to expand like so:
UnwrappedObject<TupleType> ->
UnwrappedObject<[Widget, string]> ->
[Unwrap<Widget>, Unwrap<string>] ->
[UnwrappedObject<Widget>, string] ->
[{ x: Unwrap<number> }, string] ->
[{ x: number }, string]
HOwever, instead of getting { x: number } (which is just the Widget type), we end up with 'any'. Cany anyone shed any light on this? Thanks!
Activity
CyrusNajmabadi commentedon Mar 7, 2019
Tagging Daniel Rosenwasser (@DanielRosenwasser)
CyrusNajmabadi commentedon Mar 7, 2019
Ryan Cavanaugh (@RyanCavanaugh) do you have any ideas here? Thanks!
RyanCavanaugh commentedon Mar 7, 2019
This problem was fixed by #29740
CyrusNajmabadi commentedon Mar 7, 2019
Ryan Cavanaugh (@RyanCavanaugh) Thanks! Is there a way to tell what release of TS that may have made it out into?
RyanCavanaugh commentedon Mar 7, 2019
The PR was 3 days ago, so it'd be in any nightly starting approximately yesterday
CyrusNajmabadi commentedon Mar 7, 2019
Ryan Cavanaugh (@RyanCavanaugh) wasn't it almost a month ago?
This is part of github that i'm not really familiar with!
RyanCavanaugh commentedon Mar 7, 2019
I thought today was February 7th 🤦♂️
This fix wasn't in 3.3, so "nightly" is still the right answer.
The incantation (if you have a local TS repo) to check is
CyrusNajmabadi commentedon Mar 7, 2019
That's ok. I still think it's 2017 occasionally. :D
CyrusNajmabadi commentedon Mar 8, 2019
Thanks. Have confirmed this is fixed in the latest nightly. I'm going to keep this issue open though until that is released.
Ryan Cavanaugh (@RyanCavanaugh) Daniel Rosenwasser (@DanielRosenwasser) Any general idea of when 3.4 might be released? Trying to make plans depending on if it's more like in a week or so, or more like a month. Thanks much!
typescript-bot commentedon Mar 11, 2019
This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.
RyanCavanaugh commentedon Mar 11, 2019
See #30281