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

[cacothi]

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

[sahilpurav]

I'm facing the exact same issue. It would be great if someone can get along and find the root cause or the place where the library is imported incorrectly. My application works great though!

[kgajera]

I was getting the same error. To find where it was coming from, I searched the dist directory for __read. I found that it was being included because my module was using the spread operator:

@NgModule({
  declarations: [
    ...COMPONENTS
  ],
)}

[cacothi]

It make sense as I’m using too. But I was using on the previous version and didn’t get that error.

On Sun, 23 Feb 2020 at 7:35 am, Kishan Gajera ***@***.***> wrote: I was getting the same error. To find where it was coming from, I searched the dist directory for __read. I found that it was being included because my module was using the spread operator: @NgModule({ declarations: [ ...COMPONENTS ], )} — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#1543?email_source=notifications&email_token=AC4AGT4OSE6CMU3KWVX7U73REGLDZA5CNFSM4KUSS2XKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEMVLDZI#issuecomment-590000613>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AC4AGT6Z4YTCV3CO6CIQQM3REGLDZANCNFSM4KUSS2XA> .

-- Sent from iPhone

[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: angular/angular#21280

[vltansky]

Same here

[rafa-suagu]

Some news here?

[Jack-WangZhe]

Thanks for @multimike77 's answer, but is there anyone who know why such the change will take effect?
Thanks!
Jack

[pjir]

Hey @multimike77,

Classes have a value at runtime and a type at design-time, and the use is context-sensitive.
From typescript 3.8 you should use:
import type { ...
Import type only imports declarations to be used for type annotations and declarations. It always gets fully erased, so there’s no remnant of it at runtime.

You can't mix them in one import line.

[Bil0]

Hello,
I'm getting the same WARNING by using the spead operator in a component from my lib.

The __read is imported from tslib in the compiled file but unused
import { __decorate, __read, __spread } from "tslib";

[harunergul]

In my case tree dots(...) inside one of my component cause the same error.

ngOnInit(): void { this.selectedPatient = [ ... [this.patients[0]]]; }

when ever i remove these tree dots the warning goes away.
Current warning is WARNING: '__read' is imported from external module 'tslib' but never used

any improvements?

[Dzivo]

I have same warning in angular library any news on this. Is this something to be worried about

[SchnWalter]

I wasn't able to reproduce the issue. The spread operator inside the NgModule declarations property doesn't cause any issues. @Dzivo, can you please provide a minimal repository where this issue is present?

NOTE: In this issue people talk about two different warnings with a similar message:

1. There's the warning reported in the title of this issue, for which a reproduction could be useful.
2. The warnings related to type-only imports which are related to a change in TypeScript and has nothing to do with ng-packagr, and you can find those warnings all over the place, in various projects.

[alan-agius4]

I am unable to reproduce. Please file a new issue with a reproduction if the problem persists.

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