Typescript Angular 6 7依赖的结果是一个表达式

我正在try 创建一个Angular 6库，并在Angular 6应用程序中使用它.我把它归结为一个最小的测试用例.(更新:自从Angular 7推出以来，我也try 过.)

ng new workspace # accept the defaults
ng new product # accept the defaults
cd workspace 
ng generate library widgets 
ng build --prod widgets # leave out "--prod" for Angular 7
cd ../product
ng build

一个名为"workspace"的应用程序拥有一个名为"widgets"的库.另一款名为"product"的应用程序是独立的.到目前为止一切都很好.

现在，让我们try 使用"产品"应用程序中的"小部件"库.打开CLI生成的文件product/src/app/app.module.ts.添加两行，如下所示.

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppComponent } from './app.component';
import { WidgetsModule } from '../../../workspace/dist/widgets'; //  added

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    WidgetsModule // added
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

在那次更改之后，当我从产品目录运行ng build时，我会从Webpack收到警告.

Date: 2018-07-31T13:13:08.001Z
Hash: 8a6f58d2ae959edb3cc8
Time: 8879ms
chunk {main} main.js, main.js.map (main) 15.9 kB [initial] [rendered]
chunk {polyfills} polyfills.js, polyfills.js.map (polyfills) 227 kB [initial] [rendered]
chunk {runtime} runtime.js, runtime.js.map (runtime) 5.22 kB [entry] [rendered]
chunk {styles} styles.js, styles.js.map (styles) 15.6 kB [initial] [rendered]
chunk {vendor} vendor.js, vendor.js.map (vendor) 4.59 MB [initial] [rendered]

WARNING in ../workspace/node_modules/@angular/core/fesm5/core.js
4997:15-36 Critical dependency: the request of a dependency is an expression

WARNING in ../workspace/node_modules/@angular/core/fesm5/core.js
5009:15-102 Critical dependency: the request of a dependency is an expression

"依赖的结果是一个表达式"是什么意思？我做错了什么？