Partial of interface and generic is not compiled

[aigoncharov]

TypeScript Version: 2.7.0-dev.20171121

Code

interface A {
    af: string
}
const a = <T extends {}>(): Partial<T & A> => ({ af: 'asfa' })

Link to the playground

Expected behavior:
Should compile

Actual behavior:
Compilation fails

[mhegazy]

Duplicate of #16356, and #19388. T is a generic type, and no assumption can be made about what type of af would be in T at the time it is instantiated..

[aigoncharov]

@mhegazy what if we do something like this?

interface A {
    af: string
}
const a = <T extends { af?: string }>(): Partial<T & A> => ({ af: 'asfa' })

This way we know what type af is. Though it still does not work.

[mhegazy]

it still can be more specific than string.. e.g. a<{ af: "a" }>().

[aigoncharov]

@mhegazy yeah, that's true. Sorry for creating this duplicate.