TypeScript Version: 2.3 (Playground)

Code

type Bla = { item1: number };
function f<TKey extends keyof Bla>(key: TKey) {}

f("|");

Expected behavior:
Autocomplete suggests item1 at position |.

Actual behavior:
Autocomplete does not suggest anything:

Remark
It works as expected if Bla has more than one member: