Code Coverage ignores functions like forwardRef in decorator

[CSchulz]

Which @angular/* package(s) are the source of the bug?

Don't known / other

Is this a regression?

Yes

Description

With Angular 13 we have encountered fat arrow functions like the forward ref in decorators aren't counted in coverage any longer.

@Component({
  changeDetection: ChangeDetectionStrategy.OnPush,
  templateUrl: './abschluss.component.html',
  providers: [
    {
      provide: DynamicDocumentLoader,
      useExisting: forwardRef(() => AbschlussComponent),
    },
  ],
})
export class AbschlussComponent implements DynamicDocumentLoader, OnInit {

Before Angular 13 we had 100 % code coverage and after updating to Angular 13 it looses the coverage in functions. lines and statements.
It seems to be related to the target version, we had to update it to ES2015 in the specific tsconfig.json files.

Angular 12 was still using ES5 because of the issue we found here angular/angular#44781

Angular 13:

Angular 12:

Please provide a link to a minimal reproduction of the bug

No response

Please provide the exception or error you saw

No response

Please provide the environment you discovered this bug in (run ng version)

Angular CLI: 13.3.9
Node: 16.14.2
Package Manager: npm 8.5.0
OS: win32 x64

Angular: 13.3.11
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1303.9
@angular-devkit/build-angular   13.3.9
@angular-devkit/core            13.3.9
@angular-devkit/schematics      13.3.9
@angular/cli                    13.3.9
@schematics/angular             13.3.9
ng-packagr                      13.3.1
rxjs                            7.5.6
typescript                      4.6.4

Anything else?

No response

[osaf96]

Hi @alan-agius4 can you assign this to me? would love to take a look at it.

[alan-agius4]

@osaf96, feel free to look into this and post any finding here.

[osaf96]

@alan-agius4 sure thing

[CSchulz]

It could be possible related to the @babel/core 7.8.9 and 7.8.10+ changes.

Perhaps related babel/babel#14899

[CSchulz]

It could be possible that this issue is related to a forgotten emitDecoratorMetadata in the tsconfig.spec.json and not related to angular or similar.