Better completion support for generics extending interface with optional fields

[mjbvz]

From @unional on December 15, 2016 22:49

• VSCode Version: 1.8.0

interface X {
  a?: string
}

function boo(x: X): any
function foo<T extends X>(x: T): any

Copied from original issue: microsoft/vscode#17351

[mjbvz]

Just confirmed that this behavior still appears in the latest TS 2.2 insiders builds as well.

[Sammons]

With TS2.1.4 I am running into an issue with parameter type inference

const B = <T>(f: <R extends T>(a: R) => void) => {}
/* the parameter a's signature cannot be inferred, and is not required to be a type with the "type" property */
B<{ type: number}>((a) => {
  
})

Should I open this as a separate issue? It seems similar