WARNING: '__read' is imported from external module 'tslib' but never used

Type of Issue

[ X] Bug Report
[ ] Feature Request

Description

Trying to build the package and getting the following error warning

WARNING: ‘__read’ is imported from external module ‘tslib’ but never used

Not usre where it’s been exported, but it’s not from my project.

Note, I’ve just update from Angular 8 to 9.0.1

How To Reproduce

ng build

Expected Behaviour

Success with no warning

Version Information

$ node_modules/.bin/ng-packagr --version
ng-packagr: x.y.z
@angular/*: x.y.z
typescript: x.y.z
rxjs: x.y.z
node: x.y.z
npm/yarn: x.y.z

Please include all version numbers that might be relevant, e.g. third-party libraries

[multimike77]

Something which is probably related to this problem as well. On my library project I was getting many errors like
WARNING: 'OnInit', 'OnDestroy', 'AfterContentInit' are imported from external module '@angular/core' but never used apart from having the __read is imported... erorr as described above as well.

After experimenting a bit, I found out something interesting. I could manage to make the warning about OnInit, OnDestroy, etc. disappear by separating the import statements in two:

• one which only contains imports relevant for type declarations
• all other imports, which are also used for values etc.

For example:

import { ChangeDetectionStrategy, ChangeDetectorRef, Component, OnDestroy, OnInit } from '@angular/core';

@Component({
  selector: 'lib-my-lib',
  template: `
    <p>
      my-lib works!
    </p>
  `,
  styles: [],
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class MyLibComponent implements OnInit, OnDestroy {

  constructor(
      private cd: ChangeDetectorRef
  ) { }

  ngOnInit(): void {
    this.cd.markForCheck();
  }

  ngOnDestroy(): void {
  }

}

this compiles with warning
WARNING: 'OnDestroy' and 'OnInit' are imported from external module '@angular/core' but never used.
But when changing the imports to be like

import { ChangeDetectionStrategy, Component, OnDestroy, OnInit } from '@angular/core';
import { ChangeDetectorRef } from '@angular/core';

compilation works fine without any warnings.

So somehow the compiler is no able to optimize/rewrite the import statements so that only relevant imports are kept.

Probably related to: https://github.com/angular/angular/issues/21280

[rafa-as]

Some news here?