Please add a small reproduction

Done, added.

http://plnkr.co/edit/MAVE5Mq3aaFFbUauXmRh?p=preview

Although that happened after updating to Angular 4 RC4/5

provider = webpack_require.i(WEBPACK_IMPORTED_MODULE_0__angular_core["_46" /* resolveForwardRef */])(provider);
...
else if (provider === void 0) {
_this._reportError(syntaxError("Encountered undefined provider! Usually this means you have a circular dependencies (might be caused by using 'barrel' index.ts files."));
}

Could it be a webpack related issue? So basically MockBackend is undefined running the app with a webpack-dev-server.

Please note I'm using that not for tests, but for backendless development.

Set all angular components to latest version 4.0, but reverted http module to 4.0 RC3 - and MockBackend provider now works as expected.

Are there any changes I need to consider when moving to angular 4.0?

There has been no changes.
I've just tested it using this starter and haven't got any errors. Here's my code

import {Component, NgModule} from '@angular/core'
import {MockBackend} from '@angular/http/testing'
import {BrowserModule} from '@angular/platform-browser'
import {ConnectionBackend} from '@angular/http';

@Component({
  selector: 'my-app',
  template: `
    <div>
      <h2>Hello {{name}}</h2>
    </div>
  `,
})
export class App {
  name:string;
  constructor(backend: ConnectionBackend) {
    console.log(backend);
    this.name = 'Angular!'
  }
}

@NgModule({
  imports: [ BrowserModule ],
  declarations: [ App ],
  bootstrap: [ App ],
  providers: [{provide: ConnectionBackend, useClass: MockBackend}]
})
export class AppModule {}

I believe I am seeing a similar issue.
If I build with AOT (ng build --prod):
ERROR in ./src/$$_gendir/app/app.module.ngfactory.ts
Module not found: Error: Can't resolve '@angular/http/testing/src/mock_backend' in 'C:\git\web_lcm_gatwick\src$$_gendir\app'
@ ./src/$$_gendir/app/app.module.ngfactory.ts 60:0-67
@ ./src/main.ts
@ multi ./src/main.ts

If I comment out MockBackend in my providers the issue goes away. If I disable AOT, the issue goes away.

Simple reproduction with angular-cli 1.0.0:

1. ng new ngcli
2. edit app.module.ts

import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { HttpModule } from '@angular/http';
import { MockBackend } from "@angular/http/testing";

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

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    FormsModule,
    HttpModule
  ],
  providers: [
      MockBackend
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

3. ng build --prod produces error:

ERROR in ./src/$$_gendir/app/app.module.ngfactory.ts
Module not found: Error: Can't resolve '@angular/http/testing/src/mock_backend' in 'C:\git\ngcli\src$$_gendir\app'
@ ./src/$$_gendir/app/app.module.ngfactory.ts 23:0-66
@ ./src/main.ts
@ multi ./src/main.ts

4. if you run ng build everything works fine

same problem, MockBackend not available in aot.

How i can run Angular 4 with MVC Asp.net ?? anybody please help

Just tried this again with Angular version 4.0.3 and the issue still exists.
Using my reproduction steps above >#15521 (comment)

ng build --prod or ng serve --prod produces the error.

Same problem using Angular CLI 1.0.0 and Angular 4.0.0

I'm getting this error:

ERROR in ./src/$$_gendir/app/app.module.ngfactory.ts
Module not found: Error: Can't resolve '@angular/http/testing/src/mock_backend' in '/home/mertyildiran/Documents/Tower/src/$$_gendir/app'
 @ ./src/$$_gendir/app/app.module.ngfactory.ts 26:0-66
 @ ./src/main.ts
 @ multi ./src/main.ts

You can reproduce the error with using this project of mine.

Removing MockBackend project-wide is fixing the error. But what will people do if this module is mandatory for their project?

Is there any alternative to MockBackend?

I‘ve also got the same error on angular4 or ionic2/3 with " --prod"!

Uncaught Error: Cannot find module "@angular/http/testing/src/mock_backend"

So what version will this be released in?

Confirmed fix in 4.1.2. Thanks everyone!

The issue is closed but i still get the error, i just upgraded to angular 4 (4.1.3) 2 days before, all the production code works fine, but all the tests are down, on reason is the MockBackend imported form '@angular/http/testing' is undefined.
My project don't use cli, the test is started by Karma and webpack.
the curious thing is all other angular module import works except for testing include '@angular/http/testing' and '@angular/core/testing'
Any ideas? thanks!

Same here, also webpack

issue confirmed in ng 4.0.0, building --prod
issue confimerd in ng 4.2.3, building --prod

ERROR in ./src/$$_gendir/app/app.module.ngfactory.ts
Module not found: Error: Can't resolve '@angular/http/testing/src/mock_backend' in '/Users/user/www/ng4_angle/src/$$_gendir/app'
@ ./src/$$_gendir/app/app.module.ngfactory.ts 46:0-67
@ ./src/main.ts
@ multi ./src/main.ts

I have started to use Angular 5 but it still seems that the deep imports are not working yet. My IDE automatically predicts and add import to the related but to the deep level. By removing the deep link, the app started to work fine. For example,

import { ElementRef } from '@angular/core'; // works fine but on the other hand,

import { ElementRef } from '@angular/core/src/linker/element_ref'; // throws error.

I made it to work just by removing the rest of the deep link and leaving only '@angular/core';

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}