Dependency injection and class inheritance doesn't work in Angular 8 library test

🐞 bug report

Affected Package

The issue is caused by package @angular/core@^8

Is this a regression?

Yes, the previous version in which this bug was not present was: @angular/core@7

Description

The problem occurs when:

1. The base class has a constructor with an injected service. (Injector from the example)

@Injectable()
export class BaseService {
  // "Injector" is just for the sake of example. Any injectable would have the same problem.
  constructor(public injector: Injector) {
  }
}

1. Child class has no constructor (i.e., it relies on base class constructor) AND at least one property with the default value.

@Injectable()
export class MyLibService extends BaseService {

  public foo = 'bar';

}

1. (dont ask me how I have found this, but:) In angular.json [lib name].test.options.codeCoverage should be true.

PROBLEM:

injector is undefined in the instance of MyLibService.

---

🚩 Removing property from the child class (2) AND/OR opting out codeCoverage config in angular.json (3) doesn’t brake test.

As a result, I can’t have a class inheritance and code coverage at the same time.

---

I could put a constructor in the child class and call super by passing all required arguments manually, but it’s the last option since the real-life scenario is much more complicated than the example provided here.

🔬 Minimal Reproduction

git repo: https://github.com/ddramone/ng-8-library-inheritance-di-test-bug

reproduce steps:

1. Install angular 8 cli
2. Clone git clone https://github.com/ddramone/ng-8-library-inheritance-di-test-bug.git
3. npm i
4. run Test ng test my-lib

Expected behavior

Test should pass = Injector service should be available in the service instance.

[JoostK]

I have looked into why DI doesn’t work when coverage reporting is enabled, and it can be traced back to how Angular detects whether a constructor was present in a class, or if a constructor is generated synthetically, e.g. to initialize class fields. Enabling coverage inserts coverage instrumentation statements into the generated constructors:

class MyLibService extends BaseService {
  constructor() {
    cov_8nt6qq5zt().f[2]++;
    cov_8nt6qq5zt().s[6]++;
    super(...arguments);
    cov_8nt6qq5zt().s[7]++;
    this.foo = 'bar';
  }
}

These prevent Angular from recognizing the constructor as synthesized, causing MyLibService to be instantiated with 0 arguments. The proper behavior would be to delegate to the parent constructor, allowing its dependencies to be injected.

I opened #37811 as a proposal to workaround this issue. It’s not done yet and I can’t give an ETA yet, unfortunately.

[petrce]

tested on angular 8.2.11 with cli 8.3.12 and it is still not fixed, now I have to add tons of workarounds 😦