==== tests/cases/compiler/genericSpecializations2.ts (2 errors) ====
    class IFoo<T> {
        foo<T>(x: T): T { // no error on implementors because IFoo's T is different from foo's T
            return null;
        }
    }
    
    class IntFooBad implements IFoo<number> {
        foo<string>(x: string): string { return null; }
            ~~~~~~
!!! Type parameter name cannot be 'string'
    }
    
    class StringFoo2 implements IFoo<string> {
        foo<string>(x: string): string { return null; }
            ~~~~~~
!!! Type parameter name cannot be 'string'
    }
    
    class StringFoo3 implements IFoo<string> {
        foo<T>(x: T): T { return null; }
    }