Hover type definition is wrongly inferred, but tsc type is correct

[hf]

There's a small but annoying issue in the tsserver implementation (as far as I can tell) that's been around for a long time, I'm tracking from version 2.6.

Namely, there is a mapped-type pattern I want to use, as shown in code below, and the hover type definition doesn't infer multiple levels deep. However, interestingly, tsc does infer the type correctly.

TypeScript Version: 2.6+

Code

type F<T> = (value: any) => T

function all<V>(vals: { [K in keyof V]: F<V[K]> }): (value: any) => V {
    return null as any;
}

// inspect the hover type of `x`
// it should show const x: { a: { b: any } }
const x = all({
    a: all({
        b: (value: any) => 3
    })
})(3)

// inspect the hover type of `b`
// it should show (property) b: number
x.a.b;

// and obviously this does not compile
x.a.b = 'not-a-number';

Expected behavior:

The hover type definition (and it's variants) should show

const x: { a: { b: number } }

Actual behavior:

The hover type definition for x is

const x: { a: { b: any } }

Playground Link

Related Issues: Not that I found.

[hf]

By "hover type definition" I mean the type definition shown by the editor (any which uses tsserver) when you "hover" over a symbol.

[RyanCavanaugh]

Duplicate #23897

[typescript-bot]

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