This class is visible to consumers via SomeModule -> SomeComponent, but is not exported from the top-level library entrypoint

This error happens if any component is exported in NgModuleand not included in your public_api.ts, Angular 9 will throw an error now.

This error was not coming in Angular 8 but after upgrading to Angular 9 it started showing.

If you exported any service, module or component, etc in NgModule make sure to include them in public_api.ts or else angular 9 will throw error now.

Fix: add your component to the public_api.ts

export * from './lib/components/some-me/some-me.component';

I was struggling with the same issue today.

My prerequisites:

• I work on an Angular 11 library type project;
• I have added a new directive;
• I got an error as above when tried to add my directive to module exports.

Fix:

• I have added file export to index.ts file:

export * from './just/a/relative/path/to/the/directive/{{myDirectiveFile}}';

This error will also happen when you are creating a Library and include a component incorrecty in the imports of the libary module.

import { NgModule } from '@angular/core';import { LibComponent } from './lib.component';import { ComponentWithinComponent } from './component-within/component-within.component'@NgModule({  declarations: [LibComponent, ComponentWithinComponent],  imports: [    ComponentWithinComponent  ],  exports: [LibComponent, ComponentWithinComponent]})export class LibModule { }

ng build lib //results inError NG6002: Appears in the NgModule.imports of LibModule, but could not be resolved to an NgModule class.Is it missing an @NgModule annotation?8 export class ComponentWithinComponent implements OnInit {

The fix is to remove the ComponentWithinComponent import int he lib.module like this:

@NgModule({  declarations: [LibComponent, ComponentWithinComponent],  imports: [    // don't import here  ],  exports: [LibComponent, ComponentWithinComponent]})export class LibModule { }