==== tests/cases/compiler/genericDerivedTypeWithSpecializedBase.ts (1 errors) ====
    class A<T> {
        x: T;
    }
    
    class B<U> extends A<string> {
        y: U;
    }
    
    var x: A<number>;
    var y: B<number>;
    x = y;  // error
    ~
!!! Type 'B<number>' is not assignable to type 'A<number>':
!!!   Types of property 'x' are incompatible:
!!!     Type 'string' is not assignable to type 'number'.