Better ReturnType<>; Fixes Microsoft/TypeScript#33457

[AnyhowStep]

Please verify that:

• There is an associated issue in the Backlog milestone (required)
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Fixes #33457

There's no issue in the Backlog but I figured I'd try anyway =x
It fixes my issue and only affects one other test.

But that one other test seems to only have its type emit affected?

type T19<T extends any[]> = ReturnType<(x: string, ...args: T) => T[]>;

is emitted as,

ReturnType<(x: string, ...args: T) => T[]>;

But when a concrete T is substituted in, it resolves to T[]

[typescript-bot]

It looks like you've sent a pull request to update our 'lib' files. These files aren't meant to be edited by hand, as they consist of last-known good states of the compiler and are generated from 'src'. Unless this is necessary, consider closing the pull request and sending a separate PR to update 'src'.

[typescript-bot]

It looks like you've sent a pull request to update our 'lib' files. These files aren't meant to be edited by hand, as they consist of last-known good states of the compiler and are generated from 'src'. Unless this is necessary, consider closing the pull request and sending a separate PR to update 'src'.

[AnyhowStep]

Oh. TS bot sent me a warning. Should I close this and open a PR with lib untouched?

[typescript-bot]

It looks like you've sent a pull request to update our 'lib' files. These files aren't meant to be edited by hand, as they consist of last-known good states of the compiler and are generated from 'src'. Unless this is necessary, consider closing the pull request and sending a separate PR to update 'src'.

[AnyhowStep]

Related,

#33495

The type parameter constraint and RHS of conditional type I'm using are different because of the issue outlined there.

Also, is TS bot borked or is it supposed to say that after every comment?

[typescript-bot]

It looks like you've sent a pull request to update our 'lib' files. These files aren't meant to be edited by hand, as they consist of last-known good states of the compiler and are generated from 'src'. Unless this is necessary, consider closing the pull request and sending a separate PR to update 'src'.

[typescript-bot]

It looks like you've sent a pull request to update our 'lib' files. These files aren't meant to be edited by hand, as they consist of last-known good states of the compiler and are generated from 'src'. Unless this is necessary, consider closing the pull request and sending a separate PR to update 'src'.

[typescript-bot]

It looks like you've sent a pull request to update our 'lib' files. These files aren't meant to be edited by hand, as they consist of last-known good states of the compiler and are generated from 'src'. Unless this is necessary, consider closing the pull request and sending a separate PR to update 'src'.

[AnyhowStep]

@weswigham just thought I'd show you that the TS bot hated it when I touched lib, too =P

[Jessidhia]

The ReturnType generic parameter constraint needs to be changed too.

Also, try using never[] instead of just never, maybe that helps.

[AnyhowStep]

TypeScript/src/compiler/core.ts

Line 1464 in c447ebc

export type AnyFunction = (...args: never[]) => void;

I'd just like to point out that ...args : never[] is used by the TS code base at the moment.
Just a random thought.

---

export type AnyFunction = (...args: never[]) => void;
//Expected: void
//Actual: any
type x = ReturnType<AnyFunction>;

[sandersn]

This PR hasn't seen any activity for quite a while, so I'm going to close it to keep the number of open PRs manageable. Feel free to open a fresh PR or continue the discussion on one of the linked bugs.