bug(routing): forget to put components in declaration

[indraraj26]

🐞 bug report

Affected Package

The issue is caused by package @angular/router

Is this a regression?

Yes, the previous version in which this bug was not present was: no idea

Description

Suppose you forget to declare ChildComponent in declaration of parent.module.ts and will try to use *ngFor you will get this error : Can't bind to 'ngForOf' since it isn't a known property of 'p'. Basically i forget to declare ChildComponent in parent.module.ts. Still i am able to visit /parent/children and see content.

Expected: It should throw an error that ChildComponent is not a part of any module declaration.

Issue: Sometime it is really hard to debug for newbie what went wrong.

code :

<p *ngFor="let item of [1,2,3]">
  children works!
</p>
<!--you will able to see children works even 
it is not a part of any module -->
<p>
  children works!
</p>

🔬 Minimal Reproduction

https://ng-run.com/edit/wiaLgud669oJ3gX4hMFP?open=app%2Fparent%2Fparent.component.html

🔥 Exception or Error

Can't bind to 'ngForOf' since it isn't a known property of 'p'.

🌍 Your Environment

Angular Version:

  9.0.2

Anything else relevant?

[atscott]

Duplicate of #17446. I've discussed this several times with @alxhub and there's really not a good way to do this in the NgModule world. This will be resolved by the standalone components project though (since you don't declare standalone components in a module at all).

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