Inferring within mapped tuple's type parameter raises error unexpectedly

[Semesse]

Bug Report

🔎 Search Terms

• mapped tuple

🕗 Version & Regression Information

• This is the behavior in every version I tried from 3.5.1 to the latest nightly (4.7.0-dev.20220215)

⏯ Playground Link

Playground

💻 Code

type SomeFunction = (...args: any) => any
type SomeMappedTuple<T extends readonly unknown[] | []> = { [P in keyof T]: Promise<T[P]> }
// ok if we put `infer` outside of the type parameter of SomeMappedTuple
type A<T extends SomeFunction> = T extends (...args: infer P) => any ? (...args: SomeMappedTuple<P>) => void : any
// error: A rest parameter must be of an array type
type B<T extends SomeFunction> = (...args: SomeMappedTuple<T extends (...args: infer P) => any ? P : any>) => void

// but in both cases there's no error inferring the correct type
type a = A<(a: string, b: number) => void>
type b = A<(a: string, b: number) => void>

🙁 Actual behavior

An error is raised for type B: A rest parameter must be of an array type, where the type parameter passed into SomeMappedTuple should be unknown[] or any

🙂 Expected behavior

type B should not raise any error

[RyanCavanaugh]

See #29919

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.