Cannot read property 'module' of undefined when using barrel and flatModuleOutFile

[alan-agius4]

I'm submitting a...

[x] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report  
[ ] Performance issue
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question
[ ] Other... Please describe:

Current behavior

When using flatModuleOutFile and a barrel file to register a symbol to an NgModule an error is emitted TypeError: Cannot read property 'module' of undefined.

tsconfig

  "angularCompilerOptions": {
    "flatModuleId": "index.js",
    "flatModuleOutFile": "index.js"
  }

Module file

import { NgModule } from '@angular/core';
import { LibComponent } from './lib/index';

@NgModule({
  declarations: [LibComponent]
})
export class LibModule { }

Expected behavior

Build works without any error.

Minimal reproduction of the problem with instructions

https://github.com/alan-agius4/angular-issue-24476

Environment

Angular version: 6.0.4
Typescript: 2.7.2

Related issues:

#23713

ng-packagr/ng-packagr#917
ng-packagr/ng-packagr#943

[trotyl]

Duplicate of #20931?

[alan-agius4]

yes, thanks

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