Local enum type variable can not be compared.

[mishengqiang]

TypeScript Version: 2.x

Code

enum Mode {A, B}

class C {
    m: Mode = Mode.A;
    test() {
        if (this.m !== Mode.B) {
            this.m = Mode.B
        }
        let n:Mode = Mode.A;
        if (n !== Mode.B){  // error  Operator '!==' cannot be applied to types 'Mode.A' and 'Mode.B'.
            n = Mode.A;
        }
        let l = Mode.A;
        if (l !== Mode.B){  // ok
            l = Mode.A;
        }
        console.log(this.m)
    }
}

function test(){
    let m: Mode = Mode.A;
    if (m !== Mode.B) {   // error  Operator '!==' cannot be applied to types 'Mode.A' and 'Mode.B'.
        m = Mode.B
    }
}

Expected behavior:
Local enum variable with type annotations can not be compared.
Actual behavior:
Local enum variable with type annotations can be compared.

[RyanCavanaugh]

The compiler can see your code and it can tell that you're making a comparison that's never true. See #11200