Broken type inference in generic-connected functions return type

[risen228]

Bug Report

🔎 Search Terms

generic function infer unknown type without specifying parameter type

🕗 Version & Regression Information

Faced it with 4.3.5, but it still occurs in 4.6.3 and Nightly (v4.7.0-dev.20220302)

⏯ Playground Link

Playground link with relevant code

💻 Code

interface Options<TParams, TDone, TMapped> {
    fetch: (params: TParams, foo: number) => TDone,
    map: (data: TDone) => TMapped
}

function example<TParams, TDone, TMapped>(options: Options<TParams, TDone, TMapped>) {
    return (params: TParams) => {
        const data = options.fetch(params, 123)
        return options.map(data)
    }
}

interface Params {
    one: number
    two: string
}

example({
    // WORKS
    fetch: (params: Params) => 123,
    map: (number) => String(number)
})

example({
    // WORKS
    fetch: (params: Params, foo: number) => 123,
    map: (number) => String(number)
})

example({
    // INFERS "unknown"
    fetch: (params: Params, foo) => 123,
    map: (number) => String(number)
})

🙁 Actual behavior

In 3rd example, without explicitly specifying foo parameter type, the return type of fetch function infers as unknown.
FYI: foo type infers correctly from Options inferface.

🙂 Expected behavior

The code 3rd example works like the first two examples, correctly infering the fetch function's return type.

[RyanCavanaugh]

See #47599

[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.