Ivy is not complaining about unknown element inside ng-template

🐞 bug report

Description

Ivy does not complain about an unknown element when this element is placed inside ng-template. When it’s outside of ng-template it throws a build error.

The issue can only be found in runtime (no component being rendered) or with fullTemplateTypeCheck: true.

🔬 Minimal Reproduction

1. Create a new Angular app, open the tsconfig.json and update angularCompilerOptions to

  "angularCompilerOptions": {
    "enableIvy": true
  }

1. open app.component.html and update its content to:

<ng-container *ngTemplateOutlet="test1"></ng-container>

<ng-template #test1>
   <some-component></some-component>
</ng-template>

1. Run ng serve and observe no build errors (<---- Issue here)
2. open tsconfig.json and update angularCompilerOptions to:

  "angularCompilerOptions": {
    "enableIvy": false
  }

1. Run ng serve and observe a build error
2. Open the tsconfig.json and update angularCompilerOptions to

  "angularCompilerOptions": {
    "enableIvy": true
  }

1. open app.component.html and update its content to:

<ng-container *ngTemplateOutlet="test1"></ng-container>
<some-component></some-component>

<ng-template #test1>
   <some-component></some-component>
</ng-template>

1. Run ng serve and observe a build error

🌍 Your Environment

Angular Version: 9.0.7

Please clarify if the discrepancy in the compiler behavior between steps 3 and 5 or 8 is an intended behavior.

[alxhub]

I see the fact that Ivy doesn’t complain (without fullTemplateTypeCheck mode) as a bug. We should match View Engine’s behavior, and that means running the unknown element checks even in basic mode, for the full template.

[JoostK]

I can explain that 😃

If fullTemplateTypeCheck is disabled, any ng-template (or structural directive template) in an Angular template are not type checked for compatibility reasons (the fullTemplateTypeCheck was introduced as a compatibility flag). In Ivy, disabling this flag causes any templates to be skipped during the type checking phase. This however is where these unknown elements would have been detected. Elements outside ng-template are always checked, regardless of fullTemplateTypeCheck.