Angular Non AOT compiler doesn't emit class decorators in specific cases

[ratoaq2]

🐞 bug report

Affected Package

Angular Non AOT compiler (Jit Mode)

Is this a regression?

Yes, the very same scenario works on Angular 8.x

Description

Given that AOT is disabled ("aot": false in angular.json)
Given a class that is responsible of configuring "class decorators", if I decorate a regular typescript class with a decorator generated by that class, the compiled javascript doesn't emit the class decorator properly.

class DecoratorBuilder {
  customClassDecorator<T extends { new (...args: any[]): {} }>(constructor: T) {
    console.log('Class Decorated');
    return class extends constructor {
      myName = 'Decorated Foobar';
    };
  }
}

export function ClassDecorators() {
  return new DecoratorBuilder();
}

@ClassDecorators().customClassDecorator
class MyNonAngularClass {
  myName = 'foobar';
}

🔬 Minimal Reproduction

https://github.com/ratoaq2/angular-non-aot-class-decorator

Just start the app:
npm install
npm start

access http://localhost:4200
You should see: Hello Decorated Foobar!
But you see: Hello foobar!

If you enable "aot": true, it works correctly. But that's not an option because I also face this issue in my spec tests where I can't enable aot.

🔥 Exception or Error

No exception or error

🌍 Your Environment

Angular Version:

Angular CLI: 10.0.8
Node: 12.18.4
OS: win32 x64

Angular: 10.0.14
... animations, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router
Ivy Workspace: No

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.1000.8
@angular-devkit/build-angular     0.1000.8
@angular-devkit/build-optimizer   0.1000.8
@angular-devkit/build-webpack     0.1000.8
@angular-devkit/core              10.0.8
@angular-devkit/schematics        10.0.8
@angular/cli                      10.0.8
@ngtools/webpack                  10.0.8
@schematics/angular               10.0.8
@schematics/update                0.1000.8
rxjs                              6.5.5
typescript                        3.9.7
webpack                           4.43.0

Anything else relevant?
It doesn't seem to be a typescript issue

[petebacondarwin]

I think that this is more related to the CLI processing than the framework compilation. But @alan-agius4 is looking into it.
Transferring to the CLI repo...

[petebacondarwin]

Actually it is caused by a transform (constructorParametersDownlevelTransform) that is held in the FW repository. So transferring back!

[ratoaq2]

Thanks for the quick response.
Is this kind of issue going to be fixed only on latest version 10.2.x? Or can I expect it to also be fixed on 10.0.x?

[ahnpnl]

Hi, will this be fixed for v9 as well ? Downlevel transformer in v9 locates in CLI repo but I don't see any PRs to fix this issue there for v9.

[petebacondarwin]

The PR for this issue will land on master, RC and patch branches. The patch branch is currently 10.2.x.
It will not be backported to 10.0.x nor 9.x.

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