Can not declaration merging for default exported class

TypeScript Version: 2.1.5

Code

// A *self-contained* demonstration of the problem follows...
// ===== file Foo.ts =====
export default class Foo {
  hello() { 
    console.log('Foo'); 
  }
}


// ===== file Bar.ts =====
import Foo from './Foo';

declare module './Foo' {
  interface Foo {
    add(x, y);
  }
}

// ERROR: 'add' does not exist in type Foo.
Foo.prototype.add = function (x, y) { return x + y; };

let f = new Foo();
f.hello();
f.add(3, 4);   // ERROR: 'add' does not exist in type Foo.

Expected behavior: If the class Foo is exported without default in file Foo.ts, and then import {Foo} from ‘./Foo’, it works correctly as example in doc http://www.typescriptlang.org/docs/handbook/declaration-merging.html

Hope import Foo same as import {Foo} behaviors.

Actual behavior: ERROR message showed.

[rdsedmundo]

Is there a way for augmenting a module exported with export = though? I wasn’t able to get it working.

i.e

knex.d.ts

interface Knex {
  test1: string;
}

export = Knex;

file.ts

declare module 'knex' {
  interface Knex {
    test2: string;
  }
}

[mhegazy]

You can only augment “exported” declarations. Class Foo is exported as default, and not as Foo. so the name Foo does not exist outside the module.

It just happens that default is a reserved word, and can not used as an interface declaration name.

The TS compiler needs to allow export { Foo as default} in module augmentation.