interface A1 {
    type: "A1";
}
interface A2 {
    type: "A2";
}
type AU = A1 | A2;

function foo(obj1: AU) {
    const obj2: AU = {
        type: obj1.type
        /*
        Error TS2322:
        Type '{ type: "A1" | "A2"; }' is not assignable to type 'AU'.
            Type '{ type: "A1" | "A2"; }' is not assignable to type 'A2'.
            Types of property 'type' are incompatible.
            Type '"A1" | "A2"' is not assignable to type '"A2"'.
            Type '"A1"' is not assignable to type '"A2"'.
        */

    };
}