==== tests/cases/compiler/typeParameterAssignmentCompat1.ts (4 errors) ====
    interface Foo<T> {
        frobble(value: T): T;
    }
    
    function f<T, U>(): Foo<U> {
        var x: Foo<T>;
        var y: Foo<U>;
        x = y; // should be an error
        ~
!!! Type 'Foo<U>' is not assignable to type 'Foo<T>':
!!!   Type 'U' is not assignable to type 'T'.
        return x;
               ~
!!! Type 'Foo<T>' is not assignable to type 'Foo<U>':
!!!   Type 'T' is not assignable to type 'U'.
    }
    
    class C<T> {
        f<U>(): Foo<U> {
            var x: Foo<T>;
            var y: Foo<U>;
            x = y; // should be an error
            ~
!!! Type 'Foo<U>' is not assignable to type 'Foo<T>':
!!!   Type 'U' is not assignable to type 'T'.
            return x;
                   ~
!!! Type 'Foo<T>' is not assignable to type 'Foo<U>':
!!!   Type 'T' is not assignable to type 'U'.
        }
    }