declare function doThing<
    F extends () => any
>(
    f: () => ReturnType<F>
): void;

//== This fails ==
type Bar<F extends () => any> = (
    & (() => ReturnType<F>)
    //Should be the same as `unknown`
    & (F extends any ? unknown : unknown)
);

function bar<F extends () => any>(f: F) {
    /*
        Fail
        
        Type 'ReturnType<F>' is not assignable to type
        'ReturnType<(() => ReturnType<F>) & (F extends any ? unknown : unknown)>'
        
        Type '() => any' is not assignable to type
        'F extends any ? unknown : unknown'
    */
    doThing<Bar<F>>(() : ReturnType<F> => {
        return f();
    });

    //Fail
    //Type '() => any' is not assignable to type 'F extends any ? unknown : unknown'
    const t: (
        F extends any ? unknown : unknown
    ) = ((): any => 3);

    //OK!
    const t2: (
        unknown
    ) = ((): any => 3);
}

//== This works ==
type Bar2<F extends () => any> = (
    & (() => ReturnType<F>)
    & unknown
);

function bar2<F extends () => any>(f: F) {
    //OK!
    doThing<Bar2<F>>(() : ReturnType<F> => {
        return f();
    });
}