This breaks projects built with angular-cli and rollup silently. You will see a cryptic error at runtime, something like:
Unexpected value ‘YOUR_COMPONENT’ declared by the module ‘YOUR_MODULE’. Please add a @Pipe/@Directive/@Component annotation.
…Please add a @NgModule annotation.
Angular-cli has documented this: https://github.com/angular/angular-cli/blob/master/docs/documentation/stories/linked-library.md