title: ng build --prod Cannot determine the module for class X! Add ThreadListTabsComponent to the NgModule to fix it
body: <p>I'm trying to build my Angular 5 app, and I'm getting the error:</p>
  
  <blockquote>
    <p>Cannot determine the module for class ThreadListTabsComponent in
    /home/brightwater/Differ/src/app/thread-lists/thread-lists.component.ts!
    Add ThreadListTabsComponent to the NgModule to fix it.</p>
  </blockquote>
  
  <p>This is confusing because I'm importing the offending component in the module:</p>
  
  <p><strong>thread-lists.module.ts</strong>:</p>
  
  <pre><code>import { OtherModules } from './modules-everywhere';
  import { NgModule }      from '@angular/core'
  
  import { SomeOtherComponents }  from './other-components.component';
  import { ThreadListTabsComponent } from './thread-list-tabs.component';
  
  @NgModule({
    imports: 
    [ 
      OtherModules
    ],
    declarations: [
      OtherComponents,
      ThreadListTabsComponent
    ],
    exports: [
      OtherComponents,
      ThreadListTabsComponent
    ],
    providers: [ ThreadListsService ]
  })
  
  
  export class ThreadListsModule { }
  </code></pre>
  
  <p>Here's the component:</p>
  
  <p><strong>thread-list-tabs.component.ts</strong></p>
  
  <pre><code>import { Component } from '@angular/core';
  import { Observable } from 'rxjs/Observable';
  import { Router }   from '@angular/router';
  import { ThreadListsService }   from './thread-lists.service';
  
  @Component({
    moduleId: module.id,
    selector: 'thread-list-tabs',
    templateUrl: 'thread-list-tabs.component.html',
    styleUrls: ['thread-list-tabs.component.css']
  })
  
  
  export class ThreadListTabsComponent {
  
    // Stuff this component does
  
  }
  </code></pre>
  
  <p><strong>app.module.ts</strong></p>
  
  <pre><code>import { NgModule } from '@angular/core'
  import { ThreadListsModule } from './thread-lists/thread-lists.module'
  import { OtherModules } from './other.modules'
  import { AppComponent } from './app.component'
  
  @NgModule({
    imports: [    
      OtherModules, 
      ThreadListsModule
    ],
    declarations: [ 
      AppComponent
    ],
    providers: [ SomeService ],
    bootstrap: [ AppComponent ]
  })
  
  export class AppModule { }
  </code></pre>
  
  <p>Is there something I'm missing?</p>