infer on setter argument gives unknown

Bug Report

🔎 Search Terms

setter, getter, infer

🕗 Version & Regression Information

This is the behavior in every version I tried, and I reviewed the FAQ for entries about Conditional Types

⏯ Playground Link

💻 Code

interface Test1 {
    get prop(): string;
    set prop(v: string | number);
}
type SetterType<T, K extends keyof T> = T extends {set [P in K](v: infer U);} ? U : T[K];

declare const setter: SetterType<Test1, 'prop'>; // unknown

🙁 Actual behavior

Hovering on setter gives you

const setter: unknown

🙂 Expected behavior

Hovering on setter gives you

const setter: string | number

😲 set [P in K](v: U) was never supposed to be allowed syntax. I'm honestly shocked this doesn't crash; the syntax doesn't really work at all.

The "fix" here is to make this a syntax error, at least for now.

Ryan Cavanaugh (@RyanCavanaugh)

Ryan Cavanaugh (@RyanCavanaugh) i try to get setter type, is there any solution ?

TypeScript doesn't really distinguish between accessors and regular properties at the type level, so Test1['prop'] is about the best you can do.

Ryan Cavanaugh (@RyanCavanaugh)

Ryan Cavanaugh (@RyanCavanaugh) Should TS throw the following error?

A computed property name must be of type 'string', 'number', 'symbol', or 'any'.

The error should be that get/set can't be combined with mapped types.

type Foo1<K extends string> = {[P in K]: number};
// Should error
type Foo2<K extends string> = {get [P in K](): number};
//                             ^^^^^^^^^^^^
//  Cannot combine property get/set with mapped type syntax

type A = Foo1<"prop">;
type B = Foo2<"prop">;

type AP = A["prop"];
type BP = B["prop"];
// ^ never worked anyway

I tried to work with the changes added in release 4.3 ("Separate Write Types on Properties"), but there is no way to select only those setter keys that accept a specific data type.

will this feature be added in future releases?

The future's a long time, but no this is not part of the scheduled roadmap

Wow, this is super broken...

type OH_NO = {
  get [K in WAT](): string
};

Make it fail

Oleksandr Tkachov (@Galphimbl)

Oleksandr Tkachov (@Galphimbl) You might want to follow #43729.

Correctly check computed property names in type-space get/set accesso…

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infer on setter argument gives unknown #47146

Bug Report

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🕗 Version & Regression Information

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🙂 Expected behavior

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infer on setter argument gives unknown #47146

Description

Bug Report

🔎 Search Terms

🕗 Version & Regression Information

⏯ Playground Link

💻 Code

🙁 Actual behavior

🙂 Expected behavior

Activity

RyanCavanaugh commented on Dec 14, 2021

Galphimbl commented on Dec 14, 2021

fatcerberus commented on Dec 14, 2021

a-tarasyuk commented on Dec 14, 2021

RyanCavanaugh commented on Dec 14, 2021

Galphimbl commented on Dec 14, 2021

RyanCavanaugh commented on Dec 15, 2021

RyanCavanaugh commented on Dec 15, 2021

MartinJohns commented on Dec 16, 2021

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