Autocomplete on extends keyof generic

TypeScript Version: 3.3.0-dev.20181122

Search Terms:

autocomplete
autocomplete generic
generic extends
autocomplete keyof extends
autocomplete keyof generic

Code

type Except<T, K extends keyof T> = Pick<T, { [P in keyof T]: P extends K ? never : P }[keyof T]>;

interface I1 {
    foo: string;
}
function F1<T extends I1>(): Except<T, ''> { // error is shown but autocomplete is not provided
    //code
    return null;
}

Expected behavior:
Having autocomplete showing when extending a generic

Actual behavior:
Even if error is correctly displayed, no autocomplete is shown for a T extends with a known type on the right hand.

Playground Link:
https://www.typescriptlang.org/play/index.html#src=type%20Except%3CT%2C%20K%20extends%20keyof%20T%3E%20%3D%20Pick%3CT%2C%20%7B%20%5BP%20in%20keyof%20T%5D%3A%20P%20extends%20K%20%3F%20never%20%3A%20P%20%7D%5Bkeyof%20T%5D%3E%3B%0A%0Ainterface%20I1%20%7B%0A%20%20%20%20foo%3A%20string%3B%0A%7D%0Afunction%20F1%3CT%20extends%20I1%3E()%3A%20Except%3CT%2C%20''%3E%20%7B%0A%20%20%20%20%2F%2Fcode%0A%20%20%20%20return%20null%3B%0A%7D

Related Issues:
#16740 - but this one is quite different because it's a keyof issue

I got very confused when extending the generic. Check this out for some sort of explanation why this probably isn't implemented: https://stackoverflow.com/a/58417200/7731090. I do one up your suggestion nonetheless.

I can understand why it wouldn't type, because the generic is generic . The other side of the coin is that it should at least provide values on the values it DOES know. I think it would stop some confusion and nice to have, but what drawbacks are there to consider?

I don't think about any major drawbacks; I think there will even be some good side-effects.

Going from this:

To this:

will also limit noises in Intellisense results.

I found another example (more simple).

playground

interface I1 {
    foo: number;
}

// Working
type Working = Pick<I1, 'foo'>;

// Not working
interface NotWorking extends Pick<I1, 'foo'> {}

Here's another example that seems to be caused by the same root issue:
Typescript Playground

FWIW keyof is not necessary in the generic function case. This example also does not provide type-aware autocomplete suggestions:

declare const example: <T extends 'foo'>() => unknown
example<''>()
//       ^

Any news on this issue? Still occurring as of TypeScript 5.3.3

The scenarios described above in @chrg1001's comment and in my comment would be addressed by #62170.

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Autocomplete on extends keyof generic #28662

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Autocomplete on extends keyof generic #28662

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waynevanson commented on Oct 16, 2019

lsagetlethias commented on Oct 18, 2019

chrg1001 commented on May 16, 2022

eythaann commented on Oct 17, 2022

ciriousjoker commented on Mar 17, 2023

mkantor commented on May 8, 2023

Miguel-A-Jara commented on May 6, 2025

mkantor commented on Aug 1, 2025

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