Mutually exclusive guard constraints and 'never'

[zhuravlikjb]

Applying two mutually exclusive guard constraints doesn't lead to 'never' type in the following case:

function ololo() {
    let stringOrNumber: string | number = 3 > 5 ? "a" : 7;

    if (typeof stringOrNumber === "number") {
        if (typeof stringOrNumber !== "number") {
            stringOrNumber; // shouldn't this be 'never'?
        }
    } 

Seems that it should.

[yahiko00]

Intellisense (TS 2.0.0) tells the innermost stringOrNumber is a string.

[kitsonk]

I mean you could argue that, but at the same time when the code is illogical and unreachable at run-time, why would you expect the control flow to work? What benefit would there be in coding for that?

[ahejlsberg]

This is working as intended as per #8548. There are a number of subtle issues interacting here and we haven't come up with a better place to land yet.