I'd like to be able to use union discrimination with a generic. However, it doesn't seem to be working:

Example code:

interface Foo{
    type: 'foo';
    fooProp: string
}

interface Bar{
    type: 'bar'
    barProp: number
}

interface GenericThing {
    item: T;
}


let func = (genericThing: GenericThing) => {
    if (genericThing.item.type === 'foo') {

        genericThing.item.fooProp; // this works, but type of genericThing is still GenericThing

        let fooThing = genericThing;
        fooThing.item.fooProp; //error!
    }
}

Playground

I was hoping that TypeScript would recognize that since I discriminated on the generic item property, that genericThing must be GenericThing.

Isn't this supported?

Also, kind of weird that after assignment, fooThing.item loses its discrimination.