interface Foo {
    kind: 'foo';
    a: number;
}

interface Bar {
    kind: 'bar';
    b: string;
}

function test(x: Bar|Foo) {
    if (x.kind === 'foo') {
        console.log(x.a); // Valid, as expected
    }
}

interface Qux {
    c: boolean;
}

function test2(x: (Bar|Foo)&Qux) {
    if (x.kind === 'foo') {
        // Type of x should be Foo&Qux now, but is still (Bar|Foo)&Qux
        console.log(x.a); // Error
    }
}