Null assertion operator blocking control flow anlysis

[mhegazy]

TypeScript Version: 2.9.0-dev.20180422

Search Terms:

Code

class Base { b!: number }
class Derived extends Base { d!: number; }    

declare var x: Base | undefined;

declare function isDerived(x: any): x is Derived;


if (x) { 
    if (isDerived(x!)) { 
        x // Base;
    }
    if (isDerived(x)) {
        x // Derived;
    }
}

Expected behavior:

x in both instances should have the same type.

Actual behavior:

x has two different types based on whether null assertion operator was used or not.

[RyanCavanaugh]

#15655 ?

[RyanCavanaugh]

Eh not quite. But I think there is a dupe of this somewhere

[mhegazy]

Eh not quite. But I think there is a dupe of this somewhere

yeah.. i remember seeing this before, but could not find it. my search skills are not what they used to be..

[ghost]

Duplicate of #15655 (thanks @rubenlg)

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.