"Please add a @NgModule annotation" Error on Angular2

Question

I have made a custom angular2(5.0.x) module that looks like this :

import { GuageService } from './services/guage.service';
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { GuageComponent } from './guage/guage.component';

@NgModule({
  declarations: [GuageComponent],

  imports: [
    CommonModule
  ],

  providers : [GuageService],
  exports : [GuageComponent]
})
export class GuageModule {}

I use it in my app modules like this:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { DxButtonModule, DxCircularGaugeModule } from 'devextreme-angular';
import { GuageModule } from '@kronsbi/bi-module-template';
import { HttpClientModule } from '@angular/common/http';


    import { AppComponent } from './app.component';

        @NgModule({
          declarations: [
            AppComponent
          ],
          imports: [
            BrowserModule,
            DxButtonModule,
            DxCircularGaugeModule,
            HttpClientModule,
            GuageModule
          ],
          bootstrap: [AppComponent]
        })
        export class AppModule { }

When I try to start my app I get the following error.

Unexpected value 'GuageModule' imported by the module 'AppModule'. Please add a @NgModule annotation.

UPDATE

tsconfig for the main app:

{
  "compileOnSave": false,
  "compilerOptions": {
    "outDir": "./dist/out-tsc",
    "sourceMap": true,
    "declaration": false,
    "moduleResolution": "node",
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "target": "es5",
    "typeRoots": [
      "node_modules/@types"
    ],
    "lib": [
      "es2017",
      "dom"
    ]
  }
}

ts config for the GuageModule package: {

 "compilerOptions": {
    "baseUrl": ".",
    "declaration": true,
    "stripInternal": true,
    "experimentalDecorators": true,
    "strictNullChecks": true,
    "noImplicitAny": true,
    "module": "es2015",
    "moduleResolution": "node",
    "paths": {
      "@angular/core": ["node_modules/@angular/core"],
      "rxjs/*": ["node_modules/rxjs/*"]
    },
    "rootDir": ".",
    "outDir": "dist",
    "sourceMap": true,
    "inlineSources": true,
    "target": "es5",
    "skipLibCheck": true,
    "lib": [
      "es2017", 
      "dom"
    ]
  },
  "files": [
    "index.ts"
  ],
  "angularCompilerOptions": {
    "strictMetadataEmit": true
  }
}

Answer 1

If you are using Angular 5.0 you need to add "annotationsAs": "decorators" to the "angularCompilerOptions" for your package. Angular 5 introduced new optimizations and by default the decorators are removed on compile because they are not needed at runtime. This does not work for packages as you already discovered. You can read about this in the Angular 5 announcement blog the "Build Optimizer" paragraph mentions this. Version 5.0.0 of Angular Now Available

I use this settings in my angular packages:

"angularCompilerOptions": {
      "skipTemplateCodegen": true,
      "skipMetadataEmit": false,
      "strictMetadataEmit": true,
      "annotationsAs": "decorators"
   }