fix(compiler): improve error message for undefined providers (#13546)

Closes #10835

modules/@angular/compiler/src/metadata_resolver.ts

@@ -862,11 +862,14 @@ export class CompileMetadataResolver {
       } else {
         provider = resolveForwardRef(provider);
         let providerMeta: cpl.ProviderMeta;
-        if (provider && typeof provider == 'object' && provider.hasOwnProperty('provide')) {
+        if (provider && typeof provider === 'object' && provider.hasOwnProperty('provide')) {
           this._validateProvider(provider);
           providerMeta = new cpl.ProviderMeta(provider.provide, provider);
         } else if (isValidType(provider)) {
           providerMeta = new cpl.ProviderMeta(provider, {useClass: provider});
+        } else if (provider === void 0) {
+          this._reportError(new SyntaxError(
+              `Encountered undefined provider! Usually this means you have a circular dependencies (might be caused by using 'barrel' index.ts files.`));
         } else {
           const providersInfo =
               (<string[]>providers.reduce(

modules/@angular/compiler/test/metadata_resolver_spec.ts

@@ -233,6 +233,16 @@ export function main() {
                  SyntaxError, /Invalid provider for SimpleService. useClass cannot be undefined./);
        }));
 
+    it('should throw with descriptive error message when provider is undefined',
+       inject([CompileMetadataResolver], (resolver: CompileMetadataResolver) => {
+         @NgModule({providers: [undefined]})
+         class SomeModule {
+         }
+
+         expect(() => resolver.loadNgModuleDirectiveAndPipeMetadata(SomeModule, true))
+             .toThrowError(SyntaxError, /Encountered undefined provider!/);
+       }));
+
     it('should throw with descriptive error message when one of providers is not present',
        inject([CompileMetadataResolver], (resolver: CompileMetadataResolver) => {
          @NgModule({declarations: [MyBrokenComp3]})