r3_test_bed_compiler.ts

/**
 * @license
 * Copyright Google Inc. All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import {ResourceLoader} from '@angular/compiler';
import {ApplicationInitStatus, COMPILER_OPTIONS, Compiler, Component, Directive, Injector, LOCALE_ID, ModuleWithComponentFactories, ModuleWithProviders, NgModule, NgModuleFactory, NgZone, Pipe, PlatformRef, Provider, Type, ɵDEFAULT_LOCALE_ID as DEFAULT_LOCALE_ID, ɵDirectiveDef as DirectiveDef, ɵNG_COMP_DEF as NG_COMP_DEF, ɵNG_DIR_DEF as NG_DIR_DEF, ɵNG_INJ_DEF as NG_INJ_DEF, ɵNG_MOD_DEF as NG_MOD_DEF, ɵNG_PIPE_DEF as NG_PIPE_DEF, ɵNgModuleFactory as R3NgModuleFactory, ɵNgModuleTransitiveScopes as NgModuleTransitiveScopes, ɵNgModuleType as NgModuleType, ɵRender3ComponentFactory as ComponentFactory, ɵRender3NgModuleRef as NgModuleRef, ɵcompileComponent as compileComponent, ɵcompileDirective as compileDirective, ɵcompileNgModuleDefs as compileNgModuleDefs, ɵcompilePipe as compilePipe, ɵgetInjectableDef as getInjectableDef, ɵpatchComponentDefWithScope as patchComponentDefWithScope, ɵsetLocaleId as setLocaleId, ɵtransitiveScopesFor as transitiveScopesFor, ɵɵInjectableDef as InjectableDef} from '@angular/core';
import {ModuleRegistrationMap, getRegisteredModulesState, restoreRegisteredModulesState} from '../../src/linker/ng_module_factory_registration';

import {clearResolutionOfComponentResourcesQueue, isComponentDefPendingResolution, resolveComponentResources, restoreComponentResolutionQueue} from '../../src/metadata/resource_loading';

import {MetadataOverride} from './metadata_override';
import {ComponentResolver, DirectiveResolver, NgModuleResolver, PipeResolver, Resolver} from './resolvers';
import {TestModuleMetadata} from './test_bed_common';

enum TestingModuleOverride {
  DECLARATION,
  OVERRIDE_TEMPLATE,
}

function isTestingModuleOverride(value: unknown): value is TestingModuleOverride {
  return value === TestingModuleOverride.DECLARATION ||
      value === TestingModuleOverride.OVERRIDE_TEMPLATE;
}

// Resolvers for Angular decorators
type Resolvers = {
  module: Resolver<NgModule>,
  component: Resolver<Directive>,
  directive: Resolver<Component>,
  pipe: Resolver<Pipe>,
};

interface CleanupOperation {
  field: string;
  def: any;
  original: unknown;
}

export class R3TestBedCompiler {
  private originalComponentResolutionQueue: Map<Type<any>, Component>|null = null;
  private originalRegisteredModules: null|ModuleRegistrationMap = null;

  // Testing module configuration
  private declarations: Type<any>[] = [];
  private imports: Type<any>[] = [];
  private providers: Provider[] = [];
  private schemas: any[] = [];

  // Queues of components/directives/pipes that should be recompiled.
  private pendingComponents = new Set<Type<any>>();
  private pendingDirectives = new Set<Type<any>>();
  private pendingPipes = new Set<Type<any>>();

  // Keep track of all components and directives, so we can patch Providers onto defs later.
  private seenComponents = new Set<Type<any>>();
  private seenDirectives = new Set<Type<any>>();

  // Store resolved styles for Components that have template overrides present and `styleUrls`
  // defined at the same time.
  private existingComponentStyles = new Map<Type<any>, string[]>();

  private resolvers: Resolvers = initResolvers();

  private componentToModuleScope = new Map<Type<any>, Type<any>|TestingModuleOverride>();

  // Map that keeps initial version of component/directive/pipe defs in case
  // we compile a Type again, thus overriding respective static fields. This is
  // required to make sure we restore defs to their initial states between test runs
  // TODO: we should support the case with multiple defs on a type
  private initialNgDefs = new Map<Type<any>, [string, PropertyDescriptor|undefined]>();

  // Array that keeps cleanup operations for initial versions of component/directive/pipe/module
  // defs in case TestBed makes changes to the originals.
  private defCleanupOps: CleanupOperation[] = [];

  private _injector: Injector|null = null;
  private compilerProviders: Provider[]|null = null;

  private providerOverrides: Provider[] = [];
  private rootProviderOverrides: Provider[] = [];
  private providerOverridesByToken = new Map<any, Provider>();
  private moduleProvidersOverridden = new Set<Type<any>>();

  private testModuleType: NgModuleType<any>;
  private testModuleRef: NgModuleRef<any>|null = null;

  constructor(private platform: PlatformRef, private additionalModuleTypes: Type<any>|Type<any>[]) {
    class DynamicTestModule {}
    this.testModuleType = DynamicTestModule as any;
  }

  setCompilerProviders(providers: Provider[]|null): void {
    this.compilerProviders = providers;
    this._injector = null;
  }

  configureTestingModule(moduleDef: TestModuleMetadata): void {
    // Enqueue any compilation tasks for the directly declared component.
    if (moduleDef.declarations !== undefined) {
      this.queueTypeArray(moduleDef.declarations, TestingModuleOverride.DECLARATION);
      this.declarations.push(...moduleDef.declarations);
    }

    // Enqueue any compilation tasks for imported modules.
    if (moduleDef.imports !== undefined) {
      this.queueTypesFromModulesArray(moduleDef.imports);
      this.imports.push(...moduleDef.imports);
    }

    if (moduleDef.providers !== undefined) {
      this.providers.push(...moduleDef.providers);
    }

    if (moduleDef.schemas !== undefined) {
      this.schemas.push(...moduleDef.schemas);
    }
  }

  overrideModule(ngModule: Type<any>, override: MetadataOverride<NgModule>): void {
    // Compile the module right away.
    this.resolvers.module.addOverride(ngModule, override);
    const metadata = this.resolvers.module.resolve(ngModule);
    if (metadata === null) {
      throw new Error(`${ngModule.name} is not an @NgModule or is missing metadata`);
    }

    this.recompileNgModule(ngModule);

    // At this point, the module has a valid module def (ɵmod), but the override may have introduced
    // new declarations or imported modules. Ingest any possible new types and add them to the
    // current queue.
    this.queueTypesFromModulesArray([ngModule]);
  }

  overrideComponent(component: Type<any>, override: MetadataOverride<Component>): void {
    this.resolvers.component.addOverride(component, override);
    this.pendingComponents.add(component);
  }

  overrideDirective(directive: Type<any>, override: MetadataOverride<Directive>): void {
    this.resolvers.directive.addOverride(directive, override);
    this.pendingDirectives.add(directive);
  }

  overridePipe(pipe: Type<any>, override: MetadataOverride<Pipe>): void {
    this.resolvers.pipe.addOverride(pipe, override);
    this.pendingPipes.add(pipe);
  }

  overrideProvider(
      token: any,
      provider: {useFactory?: Function, useValue?: any, deps?: any[], multi?: boolean}): void {
    const providerDef = provider.useFactory ?
        {
          provide: token,
          useFactory: provider.useFactory,
          deps: provider.deps || [],
          multi: provider.multi
        } :
        {provide: token, useValue: provider.useValue, multi: provider.multi};

    let injectableDef: InjectableDef<any>|null;
    const isRoot =
        (typeof token !== 'string' && (injectableDef = getInjectableDef(token)) &&
         injectableDef.providedIn === 'root');
    const overridesBucket = isRoot ? this.rootProviderOverrides : this.providerOverrides;
    overridesBucket.push(providerDef);

    // Keep overrides grouped by token as well for fast lookups using token
    this.providerOverridesByToken.set(token, providerDef);
  }

  overrideTemplateUsingTestingModule(type: Type<any>, template: string): void {
    const def = (type as any)[NG_COMP_DEF];
    const hasStyleUrls = (): boolean => {
      const metadata = this.resolvers.component.resolve(type) !as Component;
      return !!metadata.styleUrls && metadata.styleUrls.length > 0;
    };
    const overrideStyleUrls = !!def && !isComponentDefPendingResolution(type) && hasStyleUrls();

    // In Ivy, compiling a component does not require knowing the module providing the
    // component's scope, so overrideTemplateUsingTestingModule can be implemented purely via
    // overrideComponent. Important: overriding template requires full Component re-compilation,
    // which may fail in case styleUrls are also present (thus Component is considered as required
    // resolution). In order to avoid this, we preemptively set styleUrls to an empty array,
    // preserve current styles available on Component def and restore styles back once compilation
    // is complete.
    const override = overrideStyleUrls ? {template, styles: [], styleUrls: []} : {template};
    this.overrideComponent(type, {set: override});

    if (overrideStyleUrls && def.styles && def.styles.length > 0) {
      this.existingComponentStyles.set(type, def.styles);
    }

    // Set the component's scope to be the testing module.
    this.componentToModuleScope.set(type, TestingModuleOverride.OVERRIDE_TEMPLATE);
  }

  async compileComponents(): Promise<void> {
    this.clearComponentResolutionQueue();
    // Run compilers for all queued types.
    let needsAsyncResources = this.compileTypesSync();

    // compileComponents() should not be async unless it needs to be.
    if (needsAsyncResources) {
      let resourceLoader: ResourceLoader;
      let resolver = (url: string): Promise<string> => {
        if (!resourceLoader) {
          resourceLoader = this.injector.get(ResourceLoader);
        }
        return Promise.resolve(resourceLoader.get(url));
      };
      await resolveComponentResources(resolver);
    }
  }

  finalize(): NgModuleRef<any> {
    // One last compile
    this.compileTypesSync();

    // Create the testing module itself.
    this.compileTestModule();

    this.applyTransitiveScopes();

    this.applyProviderOverrides();

    // Patch previously stored `styles` Component values (taken from ɵcmp), in case these
    // Components have `styleUrls` fields defined and template override was requested.
    this.patchComponentsWithExistingStyles();

    // Clear the componentToModuleScope map, so that future compilations don't reset the scope of
    // every component.
    this.componentToModuleScope.clear();

    const parentInjector = this.platform.injector;
    this.testModuleRef = new NgModuleRef(this.testModuleType, parentInjector);

    // Set the locale ID, it can be overridden for the tests
    const localeId = this.testModuleRef.injector.get(LOCALE_ID, DEFAULT_LOCALE_ID);
    setLocaleId(localeId);

    // ApplicationInitStatus.runInitializers() is marked @internal to core.
    // Cast it to any before accessing it.
    (this.testModuleRef.injector.get(ApplicationInitStatus) as any).runInitializers();

    return this.testModuleRef;
  }

  /**
   * @internal
   */
  _compileNgModuleSync(moduleType: Type<any>): void {
    this.queueTypesFromModulesArray([moduleType]);
    this.compileTypesSync();
    this.applyProviderOverrides();
    this.applyProviderOverridesToModule(moduleType);
    this.applyTransitiveScopes();
  }

  /**
   * @internal
   */
  async _compileNgModuleAsync(moduleType: Type<any>): Promise<void> {
    if (this.originalRegisteredModules === null) {
      this.originalRegisteredModules = getRegisteredModulesState();
    }
    this.queueTypesFromModulesArray([moduleType]);
    await this.compileComponents();
    this.applyProviderOverrides();
    this.applyProviderOverridesToModule(moduleType);
    this.applyTransitiveScopes();
  }

  /**
   * @internal
   */
  _getModuleResolver(): Resolver<NgModule> { return this.resolvers.module; }

  /**
   * @internal
   */
  _getComponentFactories(moduleType: NgModuleType): ComponentFactory<any>[] {
    return maybeUnwrapFn(moduleType.ɵmod.declarations).reduce((factories, declaration) => {
      const componentDef = (declaration as any).ɵcmp;
      componentDef && factories.push(new ComponentFactory(componentDef, this.testModuleRef !));
      return factories;
    }, [] as ComponentFactory<any>[]);
  }

  private compileTypesSync(): boolean {
    // Compile all queued components, directives, pipes.
    let needsAsyncResources = false;
    this.pendingComponents.forEach(declaration => {
      needsAsyncResources = needsAsyncResources || isComponentDefPendingResolution(declaration);
      const metadata = this.resolvers.component.resolve(declaration) !;
      this.maybeStoreNgDef(NG_COMP_DEF, declaration);
      compileComponent(declaration, metadata);
    });
    this.pendingComponents.clear();

    this.pendingDirectives.forEach(declaration => {
      const metadata = this.resolvers.directive.resolve(declaration);
      this.maybeStoreNgDef(NG_DIR_DEF, declaration);
      compileDirective(declaration, metadata);
    });
    this.pendingDirectives.clear();

    this.pendingPipes.forEach(declaration => {
      const metadata = this.resolvers.pipe.resolve(declaration) !;
      this.maybeStoreNgDef(NG_PIPE_DEF, declaration);
      compilePipe(declaration, metadata);
    });
    this.pendingPipes.clear();

    return needsAsyncResources;
  }

  private applyTransitiveScopes(): void {
    const moduleToScope = new Map<Type<any>|TestingModuleOverride, NgModuleTransitiveScopes>();
    const getScopeOfModule =
        (moduleType: Type<any>| TestingModuleOverride): NgModuleTransitiveScopes => {
          if (!moduleToScope.has(moduleType)) {
            const realType = isTestingModuleOverride(moduleType) ? this.testModuleType : moduleType;
            moduleToScope.set(moduleType, transitiveScopesFor(realType));
          }
          return moduleToScope.get(moduleType) !;
        };

    this.componentToModuleScope.forEach((moduleType, componentType) => {
      const moduleScope = getScopeOfModule(moduleType);
      this.storeFieldOfDefOnType(componentType, NG_COMP_DEF, 'directiveDefs');
      this.storeFieldOfDefOnType(componentType, NG_COMP_DEF, 'pipeDefs');
      patchComponentDefWithScope((componentType as any).ɵcmp, moduleScope);
    });

    this.componentToModuleScope.clear();
  }

  private applyProviderOverrides(): void {
    const maybeApplyOverrides = (field: string) => (type: Type<any>) => {
      const resolver = field === NG_COMP_DEF ? this.resolvers.component : this.resolvers.directive;
      const metadata = resolver.resolve(type) !;
      if (this.hasProviderOverrides(metadata.providers)) {
        this.patchDefWithProviderOverrides(type, field);
      }
    };
    this.seenComponents.forEach(maybeApplyOverrides(NG_COMP_DEF));
    this.seenDirectives.forEach(maybeApplyOverrides(NG_DIR_DEF));

    this.seenComponents.clear();
    this.seenDirectives.clear();
  }

  private applyProviderOverridesToModule(moduleType: Type<any>): void {
    if (this.moduleProvidersOverridden.has(moduleType)) {
      return;
    }
    this.moduleProvidersOverridden.add(moduleType);

    const injectorDef: any = (moduleType as any)[NG_INJ_DEF];
    if (this.providerOverridesByToken.size > 0) {
      // Extract the list of providers from ModuleWithProviders, so we can define the final list of
      // providers that might have overrides.
      // Note: second `flatten` operation is needed to convert an array of providers
      // (e.g. `[[], []]`) into one flat list, also eliminating empty arrays.
      const providersFromModules = flatten(flatten(
          injectorDef.imports, (imported: NgModuleType<any>| ModuleWithProviders<any>) =>
                                   isModuleWithProviders(imported) ? imported.providers : []));
      const providers = [...providersFromModules, ...injectorDef.providers];
      if (this.hasProviderOverrides(providers)) {
        this.maybeStoreNgDef(NG_INJ_DEF, moduleType);

        this.storeFieldOfDefOnType(moduleType, NG_INJ_DEF, 'providers');
        injectorDef.providers = this.getOverriddenProviders(providers);
      }

      // Apply provider overrides to imported modules recursively
      const moduleDef: any = (moduleType as any)[NG_MOD_DEF];
      for (const importedModule of moduleDef.imports) {
        this.applyProviderOverridesToModule(importedModule);
      }
      // Also override the providers on any ModuleWithProviders imports since those don't appear in
      // the moduleDef.
      for (const importedModule of flatten(injectorDef.imports)) {
        if (isModuleWithProviders(importedModule)) {
          importedModule.providers = this.getOverriddenProviders(importedModule.providers);
        }
      }
    }
  }

  private patchComponentsWithExistingStyles(): void {
    this.existingComponentStyles.forEach(
        (styles, type) => (type as any)[NG_COMP_DEF].styles = styles);
    this.existingComponentStyles.clear();
  }

  private queueTypeArray(arr: any[], moduleType: Type<any>|TestingModuleOverride): void {
    for (const value of arr) {
      if (Array.isArray(value)) {
        this.queueTypeArray(value, moduleType);
      } else {
        this.queueType(value, moduleType);
      }
    }
  }

  private recompileNgModule(ngModule: Type<any>): void {
    const metadata = this.resolvers.module.resolve(ngModule);
    if (metadata === null) {
      throw new Error(`Unable to resolve metadata for NgModule: ${ngModule.name}`);
    }
    // Cache the initial ngModuleDef as it will be overwritten.
    this.maybeStoreNgDef(NG_MOD_DEF, ngModule);
    this.maybeStoreNgDef(NG_INJ_DEF, ngModule);

    compileNgModuleDefs(ngModule as NgModuleType<any>, metadata);
  }

  private queueType(type: Type<any>, moduleType: Type<any>|TestingModuleOverride): void {
    const component = this.resolvers.component.resolve(type);
    if (component) {
      // Check whether a give Type has respective NG def (ɵcmp) and compile if def is
      // missing. That might happen in case a class without any Angular decorators extends another
      // class where Component/Directive/Pipe decorator is defined.
      if (isComponentDefPendingResolution(type) || !type.hasOwnProperty(NG_COMP_DEF)) {
        this.pendingComponents.add(type);
      }
      this.seenComponents.add(type);

      // Keep track of the module which declares this component, so later the component's scope
      // can be set correctly. If the component has already been recorded here, then one of several
      // cases is true:
      // * the module containing the component was imported multiple times (common).
      // * the component is declared in multiple modules (which is an error).
      // * the component was in 'declarations' of the testing module, and also in an imported module
      //   in which case the module scope will be TestingModuleOverride.DECLARATION.
      // * overrideTemplateUsingTestingModule was called for the component in which case the module
      //   scope will be TestingModuleOverride.OVERRIDE_TEMPLATE.
      //
      // If the component was previously in the testing module's 'declarations' (meaning the
      // current value is TestingModuleOverride.DECLARATION), then `moduleType` is the component's
      // real module, which was imported. This pattern is understood to mean that the component
      // should use its original scope, but that the testing module should also contain the
      // component in its scope.
      if (!this.componentToModuleScope.has(type) ||
          this.componentToModuleScope.get(type) === TestingModuleOverride.DECLARATION) {
        this.componentToModuleScope.set(type, moduleType);
      }
      return;
    }

    const directive = this.resolvers.directive.resolve(type);
    if (directive) {
      if (!type.hasOwnProperty(NG_DIR_DEF)) {
        this.pendingDirectives.add(type);
      }
      this.seenDirectives.add(type);
      return;
    }

    const pipe = this.resolvers.pipe.resolve(type);
    if (pipe && !type.hasOwnProperty(NG_PIPE_DEF)) {
      this.pendingPipes.add(type);
      return;
    }
  }

  private queueTypesFromModulesArray(arr: any[]): void {
    for (const value of arr) {
      if (Array.isArray(value)) {
        this.queueTypesFromModulesArray(value);
      } else if (hasNgModuleDef(value)) {
        const def = value.ɵmod;
        // Look through declarations, imports, and exports, and queue everything found there.
        this.queueTypeArray(maybeUnwrapFn(def.declarations), value);
        this.queueTypesFromModulesArray(maybeUnwrapFn(def.imports));
        this.queueTypesFromModulesArray(maybeUnwrapFn(def.exports));
      }
    }
  }

  private maybeStoreNgDef(prop: string, type: Type<any>) {
    if (!this.initialNgDefs.has(type)) {
      const currentDef = Object.getOwnPropertyDescriptor(type, prop);
      this.initialNgDefs.set(type, [prop, currentDef]);
    }
  }

  private storeFieldOfDefOnType(type: Type<any>, defField: string, field: string): void {
    const def: any = (type as any)[defField];
    const original: any = def[field];
    this.defCleanupOps.push({field, def, original});
  }

  /**
   * Clears current components resolution queue, but stores the state of the queue, so we can
   * restore it later. Clearing the queue is required before we try to compile components (via
   * `TestBed.compileComponents`), so that component defs are in sync with the resolution queue.
   */
  private clearComponentResolutionQueue() {
    if (this.originalComponentResolutionQueue === null) {
      this.originalComponentResolutionQueue = new Map();
    }
    clearResolutionOfComponentResourcesQueue().forEach(
        (value, key) => this.originalComponentResolutionQueue !.set(key, value));
  }

  /*
   * Restores component resolution queue to the previously saved state. This operation is performed
   * as a part of restoring the state after completion of the current set of tests (that might
   * potentially mutate the state).
   */
  private restoreComponentResolutionQueue() {
    if (this.originalComponentResolutionQueue !== null) {
      restoreComponentResolutionQueue(this.originalComponentResolutionQueue);
      this.originalComponentResolutionQueue = null;
    }
  }

  restoreOriginalState(): void {
    // Process cleanup ops in reverse order so the field's original value is restored correctly (in
    // case there were multiple overrides for the same field).
    forEachRight(this.defCleanupOps, (op: CleanupOperation) => { op.def[op.field] = op.original; });
    // Restore initial component/directive/pipe defs
    this.initialNgDefs.forEach(
        (value: [string, PropertyDescriptor | undefined], type: Type<any>) => {
          const [prop, descriptor] = value;
          if (!descriptor) {
            // Delete operations are generally undesirable since they have performance implications
            // on objects they were applied to. In this particular case, situations where this code
            // is invoked should be quite rare to cause any noticeable impact, since it's applied
            // only to some test cases (for example when class with no annotations extends some
            // @Component) when we need to clear 'ɵcmp' field on a given class to restore
            // its original state (before applying overrides and running tests).
            delete (type as any)[prop];
          } else {
            Object.defineProperty(type, prop, descriptor);
          }
        });
    this.initialNgDefs.clear();
    this.moduleProvidersOverridden.clear();
    this.restoreComponentResolutionQueue();
    if (this.originalRegisteredModules) {
      restoreRegisteredModulesState(this.originalRegisteredModules);
      this.originalRegisteredModules = null;
    }
    // Restore the locale ID to the default value, this shouldn't be necessary but we never know
    setLocaleId(DEFAULT_LOCALE_ID);
  }

  private compileTestModule(): void {
    class RootScopeModule {}
    compileNgModuleDefs(RootScopeModule as NgModuleType<any>, {
      providers: [...this.rootProviderOverrides],
    });

    const ngZone = new NgZone({enableLongStackTrace: true});
    const providers: Provider[] = [
      {provide: NgZone, useValue: ngZone},
      {provide: Compiler, useFactory: () => new R3TestCompiler(this)},
      ...this.providers,
      ...this.providerOverrides,
    ];
    const imports = [RootScopeModule, this.additionalModuleTypes, this.imports || []];

    // clang-format off
    compileNgModuleDefs(this.testModuleType, {
      declarations: this.declarations,
      imports,
      schemas: this.schemas,
      providers,
    }, /* allowDuplicateDeclarationsInRoot */ true);
    // clang-format on

    this.applyProviderOverridesToModule(this.testModuleType);
  }

  get injector(): Injector {
    if (this._injector !== null) {
      return this._injector;
    }

    const providers: Provider[] = [];
    const compilerOptions = this.platform.injector.get(COMPILER_OPTIONS);
    compilerOptions.forEach(opts => {
      if (opts.providers) {
        providers.push(opts.providers);
      }
    });
    if (this.compilerProviders !== null) {
      providers.push(...this.compilerProviders);
    }

    // TODO(ocombe): make this work with an Injector directly instead of creating a module for it
    class CompilerModule {}
    compileNgModuleDefs(CompilerModule as NgModuleType<any>, {providers});

    const CompilerModuleFactory = new R3NgModuleFactory(CompilerModule);
    this._injector = CompilerModuleFactory.create(this.platform.injector).injector;
    return this._injector;
  }

  // get overrides for a specific provider (if any)
  private getSingleProviderOverrides(provider: Provider): Provider|null {
    const token = getProviderToken(provider);
    return this.providerOverridesByToken.get(token) || null;
  }

  private getProviderOverrides(providers?: Provider[]): Provider[] {
    if (!providers || !providers.length || this.providerOverridesByToken.size === 0) return [];
    // There are two flattening operations here. The inner flatten() operates on the metadata's
    // providers and applies a mapping function which retrieves overrides for each incoming
    // provider. The outer flatten() then flattens the produced overrides array. If this is not
    // done, the array can contain other empty arrays (e.g. `[[], []]`) which leak into the
    // providers array and contaminate any error messages that might be generated.
    return flatten(flatten(
        providers, (provider: Provider) => this.getSingleProviderOverrides(provider) || []));
  }

  private getOverriddenProviders(providers?: Provider[]): Provider[] {
    if (!providers || !providers.length || this.providerOverridesByToken.size === 0) return [];

    const flattenedProviders = flatten<Provider[]>(providers);
    const overrides = this.getProviderOverrides(flattenedProviders);
    const overriddenProviders = [...flattenedProviders, ...overrides];
    const final: Provider[] = [];
    const seenMultiProviders = new Set<Provider>();

    // We iterate through the list of providers in reverse order to make sure multi provider
    // overrides take precedence over the values defined in provider list. We also filter out all
    // multi providers that have overrides, keeping overridden values only.
    forEachRight(overriddenProviders, (provider: any) => {
      const token: any = getProviderToken(provider);
      if (isMultiProvider(provider) && this.providerOverridesByToken.has(token)) {
        // Don't add overridden multi-providers twice because when you override a multi-provider, we
        // treat it as `{multi: false}` to avoid providing the same value multiple times.
        if (!seenMultiProviders.has(token)) {
          seenMultiProviders.add(token);
          final.unshift({...provider, multi: false});
        }
      } else {
        final.unshift(provider);
      }
    });
    return final;
  }

  private hasProviderOverrides(providers?: Provider[]): boolean {
    return this.getProviderOverrides(providers).length > 0;
  }

  private patchDefWithProviderOverrides(declaration: Type<any>, field: string): void {
    const def = (declaration as any)[field];
    if (def && def.providersResolver) {
      this.maybeStoreNgDef(field, declaration);

      const resolver = def.providersResolver;
      const processProvidersFn = (providers: Provider[]) => this.getOverriddenProviders(providers);
      this.storeFieldOfDefOnType(declaration, field, 'providersResolver');
      def.providersResolver = (ngDef: DirectiveDef<any>) => resolver(ngDef, processProvidersFn);
    }
  }
}

function initResolvers(): Resolvers {
  return {
    module: new NgModuleResolver(),
    component: new ComponentResolver(),
    directive: new DirectiveResolver(),
    pipe: new PipeResolver()
  };
}

function hasNgModuleDef<T>(value: Type<T>): value is NgModuleType<T> {
  return value.hasOwnProperty('ɵmod');
}

function maybeUnwrapFn<T>(maybeFn: (() => T) | T): T {
  return maybeFn instanceof Function ? maybeFn() : maybeFn;
}

function flatten<T>(values: any[], mapFn?: (value: T) => any): T[] {
  const out: T[] = [];
  values.forEach(value => {
    if (Array.isArray(value)) {
      out.push(...flatten<T>(value, mapFn));
    } else {
      out.push(mapFn ? mapFn(value) : value);
    }
  });
  return out;
}

function getProviderField(provider: Provider, field: string) {
  return provider && typeof provider === 'object' && (provider as any)[field];
}

function getProviderToken(provider: Provider) {
  return getProviderField(provider, 'provide') || provider;
}

function isMultiProvider(provider: Provider) {
  return !!getProviderField(provider, 'multi');
}

function isModuleWithProviders(value: any): value is ModuleWithProviders<any> {
  return value.hasOwnProperty('ngModule');
}

function forEachRight<T>(values: T[], fn: (value: T, idx: number) => void): void {
  for (let idx = values.length - 1; idx >= 0; idx--) {
    fn(values[idx], idx);
  }
}

class R3TestCompiler implements Compiler {
  constructor(private testBed: R3TestBedCompiler) {}

  compileModuleSync<T>(moduleType: Type<T>): NgModuleFactory<T> {
    this.testBed._compileNgModuleSync(moduleType);
    return new R3NgModuleFactory(moduleType);
  }

  async compileModuleAsync<T>(moduleType: Type<T>): Promise<NgModuleFactory<T>> {
    await this.testBed._compileNgModuleAsync(moduleType);
    return new R3NgModuleFactory(moduleType);
  }

  compileModuleAndAllComponentsSync<T>(moduleType: Type<T>): ModuleWithComponentFactories<T> {
    const ngModuleFactory = this.compileModuleSync(moduleType);
    const componentFactories = this.testBed._getComponentFactories(moduleType as NgModuleType<T>);
    return new ModuleWithComponentFactories(ngModuleFactory, componentFactories);
  }

  async compileModuleAndAllComponentsAsync<T>(moduleType: Type<T>):
      Promise<ModuleWithComponentFactories<T>> {
    const ngModuleFactory = await this.compileModuleAsync(moduleType);
    const componentFactories = this.testBed._getComponentFactories(moduleType as NgModuleType<T>);
    return new ModuleWithComponentFactories(ngModuleFactory, componentFactories);
  }

  clearCache(): void {}

  clearCacheFor(type: Type<any>): void {}

  getModuleId(moduleType: Type<any>): string|undefined {
    const meta = this.testBed._getModuleResolver().resolve(moduleType);
    return meta && meta.id || undefined;
  }
}