Issue with module augmentation defined in another (symlinked) package

[QuentinFchx]

TypeScript Version: 2.4.2

Code

// RxPlus.ts   # npm package containing this augmentation (of rxjs), and symlinked (under "shared" name)
import { Observable } from 'rxjs';

declare module 'rxjs/Observable' {
    interface Observable<T> {
        parseInt(): Observable<number>;
    }
}

Observable.prototype.parseInt = function (this: Observable<any>) {
    return this.map(res => parseInt(res, 10));
};

// main.ts   # usage of the augmentation in another package
import 'shared/RxPlus';
import { Observable } from 'rxjs';

Observable.from([1, 2]).parseInt();
// error TS2339: Property 'parseInt' does not exist on type 'Observable<number>'.

However, the above works if the augmentation is defined in the same package than main.ts

I also did a small repro project highlighting the error.

I tried adding a declaration file to the external package, without success (I might have declared it poorly though)

It might relate to/duplicate #11406 and #12607. Also I think this stackoverflow question describes the same case (but unfortunately no answers)

Expected behavior:
A module augmentation defined in an external (symlinked) package should be working when imported into another package

Actual behavior:
The compiler is unaware of an augmentation defined in an external (symlinked) package

[QuentinFchx]

I tried to investigate a bit more: it really seems to be caused by symlinking (npm link)

On the repro project I linked above, if I copy the shared module into project/node_modules (to simulate a "true" external package, not symlinked) it works...

I added instructions on my repository. I'm sorry to insist, but can anyone just take a look at the reproduction repo and confirm or not the issue? I tried to make it small and easy to setup. 😇

Edit: Also the reason I need symlinks is because I'm using lerna

Edit2: Or is it an issue with npm link/install not flattening the dependencies tree? Leading to having rxjs (in my case) "installed" twice? Thus confusing typescript?

Edit3: It seems that #11916 (comment) solved the issue.