==== tests/cases/compiler/promiseIdentity2.ts (1 errors) ====
    interface IPromise<T, V> {
        then<U, W>(callback: (x: T) => IPromise<U, W>): IPromise<U, W>;
    }
    interface Promise<T, V> {
        then<U, W>(callback: (x: T) => Promise<T, U>): Promise<T, W>;
    }
    
    // error because T is string in the first declaration, and T is boolean in the second
    // Return type and callback return type are ok because T is any in this particular Promise
    var x: IPromise<string, number>;
    var x: Promise<any, string>;
        ~
!!! Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'IPromise<string, number>', but here has type 'Promise<any, string>'.