From 6665d76fbb37ce4248a3ed67064514ecf3c4093a Mon Sep 17 00:00:00 2001
From: Tobias Bosch <tbosch1009@gmail.com>
Date: Tue, 19 Sep 2017 11:43:34 -0700
Subject: [PATCH] perf(compiler): speed up watch mode (#19275)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

- don’t regenerate code for .d.ts files when
  an oldProgram is passed to `createProgram`
- cache `fileExists` / `getSourceFile` / `readFile` in watch mode
- refactor tests to share common code in `test_support`
- support `—diagnostic` command line to print total time
  used per watch mode compilation.
PR Close #19275
---
 packages/compiler-cli/src/compiler_host.ts    |   8 +-
 packages/compiler-cli/src/ngtools_api2.ts     |   4 +-
 packages/compiler-cli/src/perform_watch.ts    | 118 ++++--
 packages/compiler-cli/src/transformers/api.ts |  11 +
 .../src/transformers/compiler_host.ts         |  67 ++-
 .../compiler-cli/src/transformers/program.ts  |  34 +-
 .../test/diagnostics/check_types_spec.ts      |  65 +--
 .../compiler-cli/test/perform_watch_spec.ts   | 165 ++++++++
 packages/compiler-cli/test/test_support.ts    |  97 ++++-
 .../test/transformers/compiler_host_spec.ts   |   2 +-
 .../test/transformers/program_spec.ts         | 397 +++++++-----------
 11 files changed, 622 insertions(+), 346 deletions(-)
 create mode 100644 packages/compiler-cli/test/perform_watch_spec.ts

diff --git a/packages/compiler-cli/src/compiler_host.ts b/packages/compiler-cli/src/compiler_host.ts
index 903be05092..ae274f5745 100644
--- a/packages/compiler-cli/src/compiler_host.ts
+++ b/packages/compiler-cli/src/compiler_host.ts
@@ -260,7 +260,7 @@ export class CompilerHost extends BaseAotCompilerHost<CompilerHostContext> {
     this.urlResolver = createOfflineCompileUrlResolver();
   }
 
-  getMetadataForSourceFile(filePath: string): ModuleMetadata|undefined {
+  protected getSourceFile(filePath: string): ts.SourceFile {
     let sf = this.program.getSourceFile(filePath);
     if (!sf) {
       if (this.context.fileExists(filePath)) {
@@ -270,7 +270,11 @@ export class CompilerHost extends BaseAotCompilerHost<CompilerHostContext> {
         throw new Error(`Source file ${filePath} not present in program.`);
       }
     }
-    return this.metadataProvider.getMetadata(sf);
+    return sf;
+  }
+
+  getMetadataForSourceFile(filePath: string): ModuleMetadata|undefined {
+    return this.metadataProvider.getMetadata(this.getSourceFile(filePath));
   }
 
   toSummaryFileName(fileName: string, referringSrcFileName: string): string {
diff --git a/packages/compiler-cli/src/ngtools_api2.ts b/packages/compiler-cli/src/ngtools_api2.ts
index 7b6c36b536..99fdd79b8e 100644
--- a/packages/compiler-cli/src/ngtools_api2.ts
+++ b/packages/compiler-cli/src/ngtools_api2.ts
@@ -66,8 +66,9 @@ export interface CompilerHost extends ts.CompilerHost {
 export enum EmitFlags {
   DTS = 1 << 0,
   JS = 1 << 1,
+  Codegen = 1 << 4,
 
-  Default = DTS | JS
+  Default = DTS | JS | Codegen
 }
 
 export interface CustomTransformers {
@@ -106,6 +107,7 @@ export interface Program {
     customTransformers?: CustomTransformers,
     emitCallback?: TsEmitCallback
   }): ts.EmitResult;
+  getLibrarySummaries(): {fileName: string, content: string}[];
 }
 
 // Wrapper for createProgram.
diff --git a/packages/compiler-cli/src/perform_watch.ts b/packages/compiler-cli/src/perform_watch.ts
index 9f07f90a25..c83ae86b21 100644
--- a/packages/compiler-cli/src/perform_watch.ts
+++ b/packages/compiler-cli/src/perform_watch.ts
@@ -35,9 +35,25 @@ const ChangeDiagnostics = {
   },
 };
 
+function totalCompilationTimeDiagnostic(timeInMillis: number): api.Diagnostic {
+  let duration: string;
+  if (timeInMillis > 1000) {
+    duration = `${(timeInMillis / 1000).toPrecision(2)}s`;
+  } else {
+    duration = `${timeInMillis}ms`;
+  }
+  return {
+    category: ts.DiagnosticCategory.Message,
+    messageText: `Total time: ${duration}`,
+    code: api.DEFAULT_ERROR_CODE,
+    source: api.SOURCE,
+  };
+}
+
 export enum FileChangeEvent {
   Change,
-  CreateDelete
+  CreateDelete,
+  CreateDeleteDir,
 }
 
 export interface PerformWatchHost {
@@ -45,8 +61,9 @@ export interface PerformWatchHost {
   readConfiguration(): ParsedConfiguration;
   createCompilerHost(options: api.CompilerOptions): api.CompilerHost;
   createEmitCallback(options: api.CompilerOptions): api.TsEmitCallback|undefined;
-  onFileChange(listener: (event: FileChangeEvent, fileName: string) => void):
-      {close: () => void, ready: (cb: () => void) => void};
+  onFileChange(
+      options: api.CompilerOptions, listener: (event: FileChangeEvent, fileName: string) => void,
+      ready: () => void): {close: () => void};
   setTimeout(callback: () => void, ms: number): any;
   clearTimeout(timeoutId: any): void;
 }
@@ -60,23 +77,17 @@ export function createPerformWatchHost(
     createCompilerHost: options => createCompilerHost({options}),
     readConfiguration: () => readConfiguration(configFileName, existingOptions),
     createEmitCallback: options => createEmitCallback ? createEmitCallback(options) : undefined,
-    onFileChange: (listeners) => {
-      const parsed = readConfiguration(configFileName, existingOptions);
-      function stubReady(cb: () => void) { process.nextTick(cb); }
-      if (parsed.errors && parsed.errors.length) {
-        reportDiagnostics(parsed.errors);
-        return {close: () => {}, ready: stubReady};
-      }
-      if (!parsed.options.basePath) {
+    onFileChange: (options, listener, ready: () => void) => {
+      if (!options.basePath) {
         reportDiagnostics([{
           category: ts.DiagnosticCategory.Error,
           messageText: 'Invalid configuration option. baseDir not specified',
           source: api.SOURCE,
           code: api.DEFAULT_ERROR_CODE
         }]);
-        return {close: () => {}, ready: stubReady};
+        return {close: () => {}};
       }
-      const watcher = chokidar.watch(parsed.options.basePath, {
+      const watcher = chokidar.watch(options.basePath, {
         // ignore .dotfiles, .js and .map files.
         // can't ignore other files as we e.g. want to recompile if an `.html` file changes as well.
         ignored: /((^[\/\\])\..)|(\.js$)|(\.map$)|(\.metadata\.json)/,
@@ -86,15 +97,19 @@ export function createPerformWatchHost(
       watcher.on('all', (event: string, path: string) => {
         switch (event) {
           case 'change':
-            listeners(FileChangeEvent.Change, path);
+            listener(FileChangeEvent.Change, path);
             break;
           case 'unlink':
           case 'add':
-            listeners(FileChangeEvent.CreateDelete, path);
+            listener(FileChangeEvent.CreateDelete, path);
+            break;
+          case 'unlinkDir':
+          case 'addDir':
+            listener(FileChangeEvent.CreateDeleteDir, path);
             break;
         }
       });
-      function ready(cb: () => void) { watcher.on('ready', cb); }
+      watcher.on('ready', ready);
       return {close: () => watcher.close(), ready};
     },
     setTimeout: (ts.sys.clearTimeout && ts.sys.setTimeout) || setTimeout,
@@ -102,6 +117,12 @@ export function createPerformWatchHost(
   };
 }
 
+interface CacheEntry {
+  exists?: boolean;
+  sf?: ts.SourceFile;
+  content?: string;
+}
+
 /**
  * The logic in this function is adapted from `tsc.ts` from TypeScript.
  */
@@ -112,16 +133,30 @@ export function performWatchCompilation(host: PerformWatchHost):
   let cachedOptions: ParsedConfiguration|undefined;  // CompilerOptions cached from last compilation
   let timerHandleForRecompilation: any;  // Handle for 0.25s wait timer to trigger recompilation
 
-  // Watch basePath, ignoring .dotfiles
-  const fileWatcher = host.onFileChange(watchedFileChanged);
   const ingoreFilesForWatch = new Set<string>();
+  const fileCache = new Map<string, CacheEntry>();
 
   const firstCompileResult = doCompilation();
 
-  const readyPromise = new Promise(resolve => fileWatcher.ready(resolve));
+  // Watch basePath, ignoring .dotfiles
+  let resolveReadyPromise: () => void;
+  const readyPromise = new Promise(resolve => resolveReadyPromise = resolve);
+  // Note: ! is ok as options are filled after the first compilation
+  // Note: ! is ok as resolvedReadyPromise is filled by the previous call
+  const fileWatcher =
+      host.onFileChange(cachedOptions !.options, watchedFileChanged, resolveReadyPromise !);
 
   return {close, ready: cb => readyPromise.then(cb), firstCompileResult};
 
+  function cacheEntry(fileName: string): CacheEntry {
+    let entry = fileCache.get(fileName);
+    if (!entry) {
+      entry = {};
+      fileCache.set(fileName, entry);
+    }
+    return entry;
+  }
+
   function close() {
     fileWatcher.close();
     if (timerHandleForRecompilation) {
@@ -139,11 +174,8 @@ export function performWatchCompilation(host: PerformWatchHost):
       host.reportDiagnostics(cachedOptions.errors);
       return cachedOptions.errors;
     }
+    const startTime = Date.now();
     if (!cachedCompilerHost) {
-      // TODO(chuckj): consider avoiding re-generating factories for libraries.
-      // Consider modifying the AotCompilerHost to be able to remember the summary files
-      // generated from previous compiliations and return false from isSourceFile for
-      // .d.ts files for which a summary file was already generated.å
       cachedCompilerHost = host.createCompilerHost(cachedOptions.options);
       const originalWriteFileCallback = cachedCompilerHost.writeFile;
       cachedCompilerHost.writeFile = function(
@@ -152,6 +184,31 @@ export function performWatchCompilation(host: PerformWatchHost):
         ingoreFilesForWatch.add(path.normalize(fileName));
         return originalWriteFileCallback(fileName, data, writeByteOrderMark, onError, sourceFiles);
       };
+      const originalFileExists = cachedCompilerHost.fileExists;
+      cachedCompilerHost.fileExists = function(fileName: string) {
+        const ce = cacheEntry(fileName);
+        if (ce.exists == null) {
+          ce.exists = originalFileExists.call(this, fileName);
+        }
+        return ce.exists !;
+      };
+      const originalGetSourceFile = cachedCompilerHost.getSourceFile;
+      cachedCompilerHost.getSourceFile = function(
+          fileName: string, languageVersion: ts.ScriptTarget) {
+        const ce = cacheEntry(fileName);
+        if (!ce.sf) {
+          ce.sf = originalGetSourceFile.call(this, fileName, languageVersion);
+        }
+        return ce.sf !;
+      };
+      const originalReadFile = cachedCompilerHost.readFile;
+      cachedCompilerHost.readFile = function(fileName: string) {
+        const ce = cacheEntry(fileName);
+        if (ce.content == null) {
+          ce.content = originalReadFile.call(this, fileName);
+        }
+        return ce.content !;
+      };
     }
     ingoreFilesForWatch.clear();
     const compileResult = performCompilation({
@@ -166,6 +223,11 @@ export function performWatchCompilation(host: PerformWatchHost):
       host.reportDiagnostics(compileResult.diagnostics);
     }
 
+    const endTime = Date.now();
+    if (cachedOptions.options.diagnostics) {
+      const totalTime = (endTime - startTime) / 1000;
+      host.reportDiagnostics([totalCompilationTimeDiagnostic(endTime - startTime)]);
+    }
     const exitCode = exitCodeFromResult(compileResult.diagnostics);
     if (exitCode == 0) {
       cachedProgram = compileResult.program;
@@ -191,11 +253,19 @@ export function performWatchCompilation(host: PerformWatchHost):
         path.normalize(fileName) === path.normalize(cachedOptions.project)) {
       // If the configuration file changes, forget everything and start the recompilation timer
       resetOptions();
-    } else if (event === FileChangeEvent.CreateDelete) {
+    } else if (
+        event === FileChangeEvent.CreateDelete || event === FileChangeEvent.CreateDeleteDir) {
       // If a file was added or removed, reread the configuration
       // to determine the new list of root files.
       cachedOptions = undefined;
     }
+
+    if (event === FileChangeEvent.CreateDeleteDir) {
+      fileCache.clear();
+    } else {
+      fileCache.delete(fileName);
+    }
+
     if (!ingoreFilesForWatch.has(path.normalize(fileName))) {
       // Ignore the file if the file is one that was written by the compiler.
       startTimerForRecompilation();
diff --git a/packages/compiler-cli/src/transformers/api.ts b/packages/compiler-cli/src/transformers/api.ts
index eed1d0f9af..13f9081dcc 100644
--- a/packages/compiler-cli/src/transformers/api.ts
+++ b/packages/compiler-cli/src/transformers/api.ts
@@ -30,6 +30,11 @@ export function isNgDiagnostic(diagnostic: any): diagnostic is Diagnostic {
 }
 
 export interface CompilerOptions extends ts.CompilerOptions {
+  // Write statistics about compilation (e.g. total time, ...)
+  // Note: this is the --diagnostics command line option from TS (which is @internal
+  // on ts.CompilerOptions interface).
+  diagnostics?: boolean;
+
   // Absolute path to a directory where generated file structure is written.
   // If unspecified, generated files will be written alongside sources.
   // @deprecated - no effect
@@ -273,4 +278,10 @@ export interface Program {
     customTransformers?: CustomTransformers,
     emitCallback?: TsEmitCallback
   }): ts.EmitResult;
+
+  /**
+   * Returns the .ngsummary.json files of libraries that have been compiled
+   * in this program or previous programs.
+   */
+  getLibrarySummaries(): {fileName: string, content: string}[];
 }
diff --git a/packages/compiler-cli/src/transformers/compiler_host.ts b/packages/compiler-cli/src/transformers/compiler_host.ts
index 0e3f3c2831..90caee9df3 100644
--- a/packages/compiler-cli/src/transformers/compiler_host.ts
+++ b/packages/compiler-cli/src/transformers/compiler_host.ts
@@ -61,7 +61,8 @@ export class TsCompilerAotCompilerTypeCheckHostAdapter extends
   constructor(
       private rootFiles: string[], options: CompilerOptions, context: CompilerHost,
       private metadataProvider: MetadataProvider,
-      private codeGenerator: (fileName: string) => GeneratedFile[]) {
+      private codeGenerator: (fileName: string) => GeneratedFile[],
+      private summariesFromPreviousCompilations: Map<string, string>) {
     super(options, context);
     this.moduleResolutionCache = ts.createModuleResolutionCache(
         this.context.getCurrentDirectory !(), this.context.getCanonicalFileName.bind(this.context));
@@ -292,7 +293,8 @@ export class TsCompilerAotCompilerTypeCheckHostAdapter extends
     }
     this.generatedCodeFor.add(fileName);
 
-    const baseNameFromGeneratedFile = this._getBaseNameForGeneratedFile(fileName);
+    const baseNameFromGeneratedFile = this._getBaseNamesForGeneratedFile(fileName).find(
+        fileName => this.isSourceFile(fileName) && this.fileExists(fileName));
     if (baseNameFromGeneratedFile) {
       return this.ensureCodeGeneratedFor(baseNameFromGeneratedFile);
     }
@@ -336,29 +338,58 @@ export class TsCompilerAotCompilerTypeCheckHostAdapter extends
     fileName = stripNgResourceSuffix(fileName);
     // Note: Don't rely on this.generatedSourceFiles here,
     // as it might not have been filled yet.
-    if (this._getBaseNameForGeneratedFile(fileName)) {
+    if (this._getBaseNamesForGeneratedFile(fileName).find(baseFileName => {
+          if (this.isSourceFile(baseFileName)) {
+            return this.fileExists(baseFileName);
+          } else {
+            // Note: the factories of a previous program
+            // are not reachable via the regular fileExists
+            // as they might be in the outDir. So we derive their
+            // fileExist information based on the .ngsummary.json file.
+            return this.fileExists(summaryFileName(baseFileName));
+          }
+        })) {
       return true;
     }
-    return this.originalSourceFiles.has(fileName) || this.context.fileExists(fileName);
+    return this.summariesFromPreviousCompilations.has(fileName) ||
+        this.originalSourceFiles.has(fileName) || this.context.fileExists(fileName);
   }
 
-  private _getBaseNameForGeneratedFile(genFileName: string): string|null {
+  private _getBaseNamesForGeneratedFile(genFileName: string): string[] {
     const genMatch = GENERATED_FILES.exec(genFileName);
     if (genMatch) {
       const [, base, genSuffix, suffix] = genMatch;
-      // Note: on-the-fly generated files always have a `.ts` suffix,
-      // but the file from which we generated it can be a `.ts`/ `.d.ts`
-      // (see options.generateCodeForLibraries).
-      // It can also be a `.css` file in case of a `.css.ngstyle.ts` file
-      if (suffix === 'ts') {
-        const baseNames =
-            genSuffix.indexOf('ngstyle') >= 0 ? [base] : [`${base}.ts`, `${base}.d.ts`];
-        return baseNames.find(
-                   baseName => this.isSourceFile(baseName) && this.fileExists(baseName)) ||
-            null;
+      let baseNames: string[] = [];
+      if (genSuffix.indexOf('ngstyle') >= 0) {
+        // Note: ngstlye files have names like `afile.css.ngstyle.ts`
+        baseNames = [base];
+      } else if (suffix === 'd.ts') {
+        baseNames = [base + '.d.ts'];
+      } else if (suffix === 'ts') {
+        // Note: on-the-fly generated files always have a `.ts` suffix,
+        // but the file from which we generated it can be a `.ts`/ `.d.ts`
+        // (see options.generateCodeForLibraries).
+        baseNames = [`${base}.ts`, `${base}.d.ts`];
       }
+      return baseNames;
     }
-    return null;
+    return [];
+  }
+
+  loadSummary(filePath: string): string|null {
+    if (this.summariesFromPreviousCompilations.has(filePath)) {
+      return this.summariesFromPreviousCompilations.get(filePath) !;
+    }
+    return super.loadSummary(filePath);
+  }
+
+  isSourceFile(filePath: string): boolean {
+    // If we have a summary from a previous compilation,
+    // treat the file never as a source file.
+    if (this.summariesFromPreviousCompilations.has(summaryFileName(filePath))) {
+      return false;
+    }
+    return super.isSourceFile(filePath);
   }
 
   readFile = (fileName: string) => this.context.readFile(fileName);
@@ -431,3 +462,7 @@ function stripNgResourceSuffix(fileName: string): string {
 function addNgResourceSuffix(fileName: string): string {
   return `${fileName}.$ngresource$`;
 }
+
+function summaryFileName(fileName: string): string {
+  return fileName.replace(EXT, '') + '.ngsummary.json';
+}
\ No newline at end of file
diff --git a/packages/compiler-cli/src/transformers/program.ts b/packages/compiler-cli/src/transformers/program.ts
index c256645dcb..54cc9ed527 100644
--- a/packages/compiler-cli/src/transformers/program.ts
+++ b/packages/compiler-cli/src/transformers/program.ts
@@ -35,6 +35,9 @@ const defaultEmitCallback: TsEmitCallback =
 
 class AngularCompilerProgram implements Program {
   private metadataCache: LowerMetadataCache;
+  private summariesFromPreviousCompilations = new Map<string, string>();
+  // Note: This will be cleared out as soon as we create the _tsProgram
+  private oldTsProgram: ts.Program|undefined;
   private _emittedGenFiles: GeneratedFile[]|undefined;
 
   // Lazily initialized fields
@@ -54,6 +57,11 @@ class AngularCompilerProgram implements Program {
     if (Number(major) < 2 || (Number(major) === 2 && Number(minor) < 4)) {
       throw new Error('The Angular Compiler requires TypeScript >= 2.4.');
     }
+    this.oldTsProgram = oldProgram ? oldProgram.getTsProgram() : undefined;
+    if (oldProgram) {
+      oldProgram.getLibrarySummaries().forEach(
+          ({content, fileName}) => this.summariesFromPreviousCompilations.set(fileName, content));
+    }
 
     this.rootNames = rootNames = rootNames.filter(r => !GENERATED_FILES.test(r));
     if (options.flatModuleOutFile) {
@@ -75,6 +83,23 @@ class AngularCompilerProgram implements Program {
     this.metadataCache = new LowerMetadataCache({quotedNames: true}, !!options.strictMetadataEmit);
   }
 
+  getLibrarySummaries(): {fileName: string, content: string}[] {
+    const emittedLibSummaries: {fileName: string, content: string}[] = [];
+    this.summariesFromPreviousCompilations.forEach(
+        (content, fileName) => emittedLibSummaries.push({fileName, content}));
+    if (this._emittedGenFiles) {
+      this._emittedGenFiles.forEach(genFile => {
+        if (genFile.srcFileUrl.endsWith('.d.ts') &&
+            genFile.genFileUrl.endsWith('.ngsummary.json')) {
+          // Note: ! is ok here as ngsummary.json files are always plain text, so genFile.source
+          // is filled.
+          emittedLibSummaries.push({fileName: genFile.genFileUrl, content: genFile.source !});
+        }
+      });
+    }
+    return emittedLibSummaries;
+  }
+
   getTsProgram(): ts.Program { return this.tsProgram; }
 
   getTsOptionDiagnostics(cancellationToken?: ts.CancellationToken) {
@@ -284,6 +309,9 @@ class AngularCompilerProgram implements Program {
     if (this._analyzedModules) {
       throw new Error(`Internal Error: already initalized!`);
     }
+    // Note: This is important to not produce a memory leak!
+    const oldTsProgram = this.oldTsProgram;
+    this.oldTsProgram = undefined;
     const analyzedFiles: NgAnalyzedFile[] = [];
     const codegen = (fileName: string) => {
       if (this._analyzedModules) {
@@ -295,15 +323,13 @@ class AngularCompilerProgram implements Program {
       return this._compiler.emitBasicStubs(analyzedFile);
     };
     const hostAdapter = new TsCompilerAotCompilerTypeCheckHostAdapter(
-        this.rootNames, this.options, this.host, this.metadataCache, codegen);
+        this.rootNames, this.options, this.host, this.metadataCache, codegen,
+        this.summariesFromPreviousCompilations);
     const aotOptions = getAotCompilerOptions(this.options);
     this._compiler = createAotCompiler(hostAdapter, aotOptions).compiler;
     this._typeCheckHost = hostAdapter;
     this._structuralDiagnostics = [];
 
-    const oldTsProgram = this.oldProgram ? this.oldProgram.getTsProgram() : undefined;
-    // Note: This is important to not produce a memory leak!
-    this.oldProgram = undefined;
     const tmpProgram = ts.createProgram(this.rootNames, this.options, hostAdapter, oldTsProgram);
     return {tmpProgram, analyzedFiles, hostAdapter};
   }
diff --git a/packages/compiler-cli/test/diagnostics/check_types_spec.ts b/packages/compiler-cli/test/diagnostics/check_types_spec.ts
index a7d505a6f3..8acb3604df 100644
--- a/packages/compiler-cli/test/diagnostics/check_types_spec.ts
+++ b/packages/compiler-cli/test/diagnostics/check_types_spec.ts
@@ -7,84 +7,41 @@
  */
 
 import * as ng from '@angular/compiler-cli';
-import {makeTempDir} from '@angular/tsc-wrapped/test/test_support';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as ts from 'typescript';
 
-function getNgRootDir() {
-  const moduleFilename = module.filename.replace(/\\/g, '/');
-  const distIndex = moduleFilename.indexOf('/dist/all');
-  return moduleFilename.substr(0, distIndex);
-}
+import {TestSupport, expectNoDiagnostics, setup} from '../test_support';
 
 describe('ng type checker', () => {
-  let basePath: string;
-  let write: (fileName: string, content: string) => void;
   let errorSpy: jasmine.Spy&((s: string) => void);
+  let testSupport: TestSupport;
 
   function compileAndCheck(
       mockDirs: {[fileName: string]: string}[],
       overrideOptions: ng.CompilerOptions = {}): ng.Diagnostics {
+    testSupport.writeFiles(...mockDirs);
     const fileNames: string[] = [];
     mockDirs.forEach((dir) => {
       Object.keys(dir).forEach((fileName) => {
         if (fileName.endsWith('.ts')) {
-          fileNames.push(path.resolve(basePath, fileName));
+          fileNames.push(path.resolve(testSupport.basePath, fileName));
         }
-        write(fileName, dir[fileName]);
       });
     });
-    const options: ng.CompilerOptions = {
-      basePath,
-      'experimentalDecorators': true,
-      'skipLibCheck': true,
-      'strict': true,
-      'types': [],
-      'outDir': path.resolve(basePath, 'built'),
-      'rootDir': basePath,
-      'baseUrl': basePath,
-      'declaration': true,
-      'target': ts.ScriptTarget.ES5,
-      'module': ts.ModuleKind.ES2015,
-      'moduleResolution': ts.ModuleResolutionKind.NodeJs,
-      'lib': [
-        path.resolve(basePath, 'node_modules/typescript/lib/lib.es6.d.ts'),
-        path.resolve(basePath, 'node_modules/typescript/lib/lib.dom.d.ts')
-      ],
-      'typeRoots': [path.resolve(basePath, 'node_modules/@types')], ...overrideOptions
-    };
+    const options = testSupport.createCompilerOptions(overrideOptions);
     const {diagnostics} = ng.performCompilation({rootNames: fileNames, options});
     return diagnostics;
   }
 
   beforeEach(() => {
     errorSpy = jasmine.createSpy('consoleError').and.callFake(console.error);
-    basePath = makeTempDir();
-    write = (fileName: string, content: string) => {
-      const dir = path.dirname(fileName);
-      if (dir != '.') {
-        const newDir = path.join(basePath, dir);
-        if (!fs.existsSync(newDir)) fs.mkdirSync(newDir);
-      }
-      fs.writeFileSync(path.join(basePath, fileName), content, {encoding: 'utf-8'});
-    };
-    const ngRootDir = getNgRootDir();
-    const nodeModulesPath = path.resolve(basePath, 'node_modules');
-    fs.mkdirSync(nodeModulesPath);
-    fs.symlinkSync(
-        path.resolve(ngRootDir, 'dist', 'all', '@angular'),
-        path.resolve(nodeModulesPath, '@angular'));
-    fs.symlinkSync(
-        path.resolve(ngRootDir, 'node_modules', 'rxjs'), path.resolve(nodeModulesPath, 'rxjs'));
-    fs.symlinkSync(
-        path.resolve(ngRootDir, 'node_modules', 'typescript'),
-        path.resolve(nodeModulesPath, 'typescript'));
+    testSupport = setup();
   });
 
   function accept(
       files: {[fileName: string]: string} = {}, overrideOptions: ng.CompilerOptions = {}) {
-    expectNoDiagnostics(compileAndCheck([QUICKSTART, files], overrideOptions));
+    expectNoDiagnostics({}, compileAndCheck([QUICKSTART, files], overrideOptions));
   }
 
   function reject(
@@ -193,7 +150,7 @@ describe('ng type checker', () => {
 
   describe('with lowered expressions', () => {
     it('should not report lowered expressions as errors',
-       () => { expectNoDiagnostics(compileAndCheck([LOWERING_QUICKSTART])); });
+       () => { expectNoDiagnostics({}, compileAndCheck([LOWERING_QUICKSTART])); });
   });
 });
 
@@ -284,9 +241,3 @@ const LOWERING_QUICKSTART = {
     export class AppModule { }
   `
 };
-
-function expectNoDiagnostics(diagnostics: ng.Diagnostics) {
-  if (diagnostics && diagnostics.length) {
-    throw new Error(ng.formatDiagnostics({}, diagnostics));
-  }
-}
diff --git a/packages/compiler-cli/test/perform_watch_spec.ts b/packages/compiler-cli/test/perform_watch_spec.ts
new file mode 100644
index 0000000000..767eec82fd
--- /dev/null
+++ b/packages/compiler-cli/test/perform_watch_spec.ts
@@ -0,0 +1,165 @@
+/**
+ * @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 * as fs from 'fs';
+import * as path from 'path';
+import * as ts from 'typescript';
+
+import * as ng from '../index';
+import {FileChangeEvent, performWatchCompilation} from '../src/perform_watch';
+
+import {TestSupport, expectNoDiagnostics, setup} from './test_support';
+
+describe('perform watch', () => {
+  let testSupport: TestSupport;
+  let outDir: string;
+
+  beforeEach(() => {
+    testSupport = setup();
+    outDir = path.resolve(testSupport.basePath, 'outDir');
+  });
+
+  function createConfig(): ng.ParsedConfiguration {
+    const options = testSupport.createCompilerOptions({outDir});
+    return {
+      options,
+      rootNames: [path.resolve(testSupport.basePath, 'src/index.ts')],
+      project: path.resolve(testSupport.basePath, 'src/tsconfig.json'),
+      emitFlags: ng.EmitFlags.Default,
+      errors: []
+    };
+  }
+
+  it('should compile files during the initial run', () => {
+    const config = createConfig();
+    const host = new MockWatchHost(config);
+
+    testSupport.writeFiles({
+      'src/main.ts': createModuleAndCompSource('main'),
+      'src/index.ts': `export * from './main'; `,
+    });
+
+    const watchResult = performWatchCompilation(host);
+    expectNoDiagnostics(config.options, watchResult.firstCompileResult);
+
+    expect(fs.existsSync(path.resolve(outDir, 'src', 'main.ngfactory.js'))).toBe(true);
+  });
+
+  it('should cache files on subsequent runs', () => {
+    const config = createConfig();
+    const host = new MockWatchHost(config);
+    let fileExistsSpy: jasmine.Spy;
+    let getSourceFileSpy: jasmine.Spy;
+    host.createCompilerHost = (options: ng.CompilerOptions) => {
+      const ngHost = ng.createCompilerHost({options});
+      fileExistsSpy = spyOn(ngHost, 'fileExists').and.callThrough();
+      getSourceFileSpy = spyOn(ngHost, 'getSourceFile').and.callThrough();
+      return ngHost;
+    };
+
+    testSupport.writeFiles({
+      'src/main.ts': createModuleAndCompSource('main'),
+      'src/util.ts': `export const x = 1;`,
+      'src/index.ts': `
+        export * from './main';
+        export * from './util';
+      `,
+    });
+
+    const mainTsPath = path.resolve(testSupport.basePath, 'src', 'main.ts');
+    const utilTsPath = path.resolve(testSupport.basePath, 'src', 'util.ts');
+    const mainNgFactory = path.resolve(outDir, 'src', 'main.ngfactory.js');
+    performWatchCompilation(host);
+    expect(fs.existsSync(mainNgFactory)).toBe(true);
+    expect(fileExistsSpy !).toHaveBeenCalledWith(mainTsPath);
+    expect(fileExistsSpy !).toHaveBeenCalledWith(utilTsPath);
+    expect(getSourceFileSpy !).toHaveBeenCalledWith(mainTsPath, ts.ScriptTarget.ES5);
+    expect(getSourceFileSpy !).toHaveBeenCalledWith(utilTsPath, ts.ScriptTarget.ES5);
+
+    fileExistsSpy !.calls.reset();
+    getSourceFileSpy !.calls.reset();
+
+    // trigger a single file change
+    // -> all other files should be cached
+    fs.unlinkSync(mainNgFactory);
+    host.triggerFileChange(FileChangeEvent.Change, utilTsPath);
+
+    expect(fs.existsSync(mainNgFactory)).toBe(true);
+    expect(fileExistsSpy !).not.toHaveBeenCalledWith(mainTsPath);
+    expect(fileExistsSpy !).toHaveBeenCalledWith(utilTsPath);
+    expect(getSourceFileSpy !).not.toHaveBeenCalledWith(mainTsPath, ts.ScriptTarget.ES5);
+    expect(getSourceFileSpy !).toHaveBeenCalledWith(utilTsPath, ts.ScriptTarget.ES5);
+
+    // trigger a folder change
+    // -> nothing should be cached
+    fs.unlinkSync(mainNgFactory);
+    host.triggerFileChange(
+        FileChangeEvent.CreateDeleteDir, path.resolve(testSupport.basePath, 'src'));
+
+    expect(fs.existsSync(mainNgFactory)).toBe(true);
+    expect(fileExistsSpy !).toHaveBeenCalledWith(mainTsPath);
+    expect(fileExistsSpy !).toHaveBeenCalledWith(utilTsPath);
+    expect(getSourceFileSpy !).toHaveBeenCalledWith(mainTsPath, ts.ScriptTarget.ES5);
+    expect(getSourceFileSpy !).toHaveBeenCalledWith(utilTsPath, ts.ScriptTarget.ES5);
+  });
+});
+
+function createModuleAndCompSource(prefix: string, template: string = prefix + 'template') {
+  const templateEntry =
+      template.endsWith('.html') ? `templateUrl: '${template}'` : `template: \`${template}\``;
+  return `
+    import {Component, NgModule} from '@angular/core';
+
+    @Component({selector: '${prefix}', ${templateEntry}})
+    export class ${prefix}Comp {}
+
+    @NgModule({declarations: [${prefix}Comp]})
+    export class ${prefix}Module {}
+  `;
+}
+
+class MockWatchHost {
+  timeoutListeners: Array<(() => void)|null> = [];
+  fileChangeListeners: Array<((event: FileChangeEvent, fileName: string) => void)|null> = [];
+  diagnostics: ng.Diagnostics = [];
+  constructor(public config: ng.ParsedConfiguration) {}
+
+  reportDiagnostics(diags: ng.Diagnostics) { this.diagnostics.push(...diags); }
+  readConfiguration() { return this.config; }
+  createCompilerHost(options: ng.CompilerOptions) { return ng.createCompilerHost({options}); };
+  createEmitCallback() { return undefined; }
+  onFileChange(
+      options: ng.CompilerOptions, listener: (event: FileChangeEvent, fileName: string) => void,
+      ready: () => void) {
+    const id = this.fileChangeListeners.length;
+    this.fileChangeListeners.push(listener);
+    ready();
+    return {
+      close: () => this.fileChangeListeners[id] = null,
+    };
+  }
+  setTimeout(callback: () => void, ms: number): any {
+    const id = this.timeoutListeners.length;
+    this.timeoutListeners.push(callback);
+    return id;
+  }
+  clearTimeout(timeoutId: any): void { this.timeoutListeners[timeoutId] = null; }
+  flushTimeouts() {
+    this.timeoutListeners.forEach(cb => {
+      if (cb) cb();
+    });
+  }
+  triggerFileChange(event: FileChangeEvent, fileName: string) {
+    this.fileChangeListeners.forEach(listener => {
+      if (listener) {
+        listener(event, fileName);
+      }
+    });
+    this.flushTimeouts();
+  }
+}
diff --git a/packages/compiler-cli/test/test_support.ts b/packages/compiler-cli/test/test_support.ts
index feb27463bd..8845e2275d 100644
--- a/packages/compiler-cli/test/test_support.ts
+++ b/packages/compiler-cli/test/test_support.ts
@@ -9,9 +9,17 @@
 import * as fs from 'fs';
 import * as os from 'os';
 import * as path from 'path';
+import * as ts from 'typescript';
+import * as ng from '../index';
 
 const tmpdir = process.env.TEST_TMPDIR || os.tmpdir();
 
+function getNgRootDir() {
+  const moduleFilename = module.filename.replace(/\\/g, '/');
+  const distIndex = moduleFilename.indexOf('/dist/all');
+  return moduleFilename.substr(0, distIndex);
+}
+
 export function writeTempFile(name: string, contents: string): string {
   // TEST_TMPDIR is set by bazel.
   const id = (Math.random() * 1000000).toFixed(0);
@@ -25,4 +33,91 @@ export function makeTempDir(): string {
   const dir = path.join(tmpdir, `tmp.${id}`);
   fs.mkdirSync(dir);
   return dir;
-}
\ No newline at end of file
+}
+
+export interface TestSupport {
+  basePath: string;
+  write(fileName: string, content: string): void;
+  writeFiles(...mockDirs: {[fileName: string]: string}[]): void;
+  createCompilerOptions(overrideOptions?: ng.CompilerOptions): ng.CompilerOptions;
+  shouldExist(fileName: string): void;
+  shouldNotExist(fileName: string): void;
+}
+
+export function setup(): TestSupport {
+  const basePath = makeTempDir();
+
+  const ngRootDir = getNgRootDir();
+  const nodeModulesPath = path.resolve(basePath, 'node_modules');
+  fs.mkdirSync(nodeModulesPath);
+  fs.symlinkSync(
+      path.resolve(ngRootDir, 'dist', 'all', '@angular'),
+      path.resolve(nodeModulesPath, '@angular'));
+  fs.symlinkSync(
+      path.resolve(ngRootDir, 'node_modules', 'rxjs'), path.resolve(nodeModulesPath, 'rxjs'));
+  fs.symlinkSync(
+      path.resolve(ngRootDir, 'node_modules', 'typescript'),
+      path.resolve(nodeModulesPath, 'typescript'));
+
+  return {basePath, write, writeFiles, createCompilerOptions, shouldExist, shouldNotExist};
+
+  function write(fileName: string, content: string) {
+    const dir = path.dirname(fileName);
+    if (dir != '.') {
+      const newDir = path.join(basePath, dir);
+      if (!fs.existsSync(newDir)) fs.mkdirSync(newDir);
+    }
+    fs.writeFileSync(path.join(basePath, fileName), content, {encoding: 'utf-8'});
+  }
+
+  function writeFiles(...mockDirs: {[fileName: string]: string}[]) {
+    mockDirs.forEach(
+        (dir) => { Object.keys(dir).forEach((fileName) => { write(fileName, dir[fileName]); }); });
+  }
+
+  function createCompilerOptions(overrideOptions: ng.CompilerOptions = {}): ng.CompilerOptions {
+    return {
+      basePath,
+      'experimentalDecorators': true,
+      'skipLibCheck': true,
+      'strict': true,
+      'types': [],
+      'outDir': path.resolve(basePath, 'built'),
+      'rootDir': basePath,
+      'baseUrl': basePath,
+      'declaration': true,
+      'target': ts.ScriptTarget.ES5,
+      'module': ts.ModuleKind.ES2015,
+      'moduleResolution': ts.ModuleResolutionKind.NodeJs,
+      'lib': [
+        path.resolve(basePath, 'node_modules/typescript/lib/lib.es6.d.ts'),
+      ],
+      ...overrideOptions,
+    };
+  }
+
+  function shouldExist(fileName: string) {
+    if (!fs.existsSync(path.resolve(basePath, fileName))) {
+      throw new Error(`Expected ${fileName} to be emitted (basePath: ${basePath})`);
+    }
+  }
+
+  function shouldNotExist(fileName: string) {
+    if (fs.existsSync(path.resolve(basePath, fileName))) {
+      throw new Error(`Did not expect ${fileName} to be emitted (basePath: ${basePath})`);
+    }
+  }
+}
+
+export function expectNoDiagnostics(options: ng.CompilerOptions, diags: ng.Diagnostics) {
+  if (diags.length) {
+    throw new Error(`Expected no diagnostics: ${ng.formatDiagnostics(options, diags)}`);
+  }
+}
+
+export function expectNoDiagnosticsInProgram(options: ng.CompilerOptions, p: ng.Program) {
+  expectNoDiagnostics(options, [
+    ...p.getNgStructuralDiagnostics(), ...p.getTsSemanticDiagnostics(),
+    ...p.getNgSemanticDiagnostics()
+  ]);
+}
diff --git a/packages/compiler-cli/test/transformers/compiler_host_spec.ts b/packages/compiler-cli/test/transformers/compiler_host_spec.ts
index 5364dfa7ca..404040c31b 100644
--- a/packages/compiler-cli/test/transformers/compiler_host_spec.ts
+++ b/packages/compiler-cli/test/transformers/compiler_host_spec.ts
@@ -39,7 +39,7 @@ describe('NgCompilerHost', () => {
     ngHost = createNgHost({files}),
   }: {files?: Directory, options?: CompilerOptions, ngHost?: CompilerHost} = {}) {
     return new TsCompilerAotCompilerTypeCheckHostAdapter(
-        ['/tmp/index.ts'], options, ngHost, new MetadataCollector(), codeGenerator);
+        ['/tmp/index.ts'], options, ngHost, new MetadataCollector(), codeGenerator, new Map());
   }
 
   describe('fileNameToModuleName', () => {
diff --git a/packages/compiler-cli/test/transformers/program_spec.ts b/packages/compiler-cli/test/transformers/program_spec.ts
index 65c1fba161..0ba960e608 100644
--- a/packages/compiler-cli/test/transformers/program_spec.ts
+++ b/packages/compiler-cli/test/transformers/program_spec.ts
@@ -7,288 +7,205 @@
  */
 
 import * as ng from '@angular/compiler-cli';
-import {makeTempDir} from '@angular/tsc-wrapped/test/test_support';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as ts from 'typescript';
 
-import {StructureIsReused, tsStructureIsReused} from '../../src/transformers/util';
-
-function getNgRootDir() {
-  const moduleFilename = module.filename.replace(/\\/g, '/');
-  const distIndex = moduleFilename.indexOf('/dist/all');
-  return moduleFilename.substr(0, distIndex);
-}
+import {CompilerHost} from '../../src/transformers/api';
+import {GENERATED_FILES, StructureIsReused, tsStructureIsReused} from '../../src/transformers/util';
+import {TestSupport, expectNoDiagnosticsInProgram, setup} from '../test_support';
 
 describe('ng program', () => {
-  let basePath: string;
-  let write: (fileName: string, content: string) => void;
+  let testSupport: TestSupport;
   let errorSpy: jasmine.Spy&((s: string) => void);
 
-  function writeFiles(...mockDirs: {[fileName: string]: string}[]) {
-    mockDirs.forEach(
-        (dir) => { Object.keys(dir).forEach((fileName) => { write(fileName, dir[fileName]); }); });
-  }
-
-  function createCompilerOptions(overrideOptions: ng.CompilerOptions = {}): ng.CompilerOptions {
-    return {
-      basePath,
-      'experimentalDecorators': true,
-      'skipLibCheck': true,
-      'strict': true,
-      'types': [],
-      'outDir': path.resolve(basePath, 'built'),
-      'rootDir': basePath,
-      'baseUrl': basePath,
-      'declaration': true,
-      'target': ts.ScriptTarget.ES5,
-      'module': ts.ModuleKind.ES2015,
-      'moduleResolution': ts.ModuleResolutionKind.NodeJs,
-      'lib': [
-        path.resolve(basePath, 'node_modules/typescript/lib/lib.es6.d.ts'),
-        path.resolve(basePath, 'node_modules/typescript/lib/lib.dom.d.ts')
-      ],
-      'typeRoots': [path.resolve(basePath, 'node_modules/@types')], ...overrideOptions,
-    };
-  }
-
-  function expectNoDiagnostics(options: ng.CompilerOptions, p: ng.Program) {
-    const diags: ng.Diagnostics =
-        [...p.getTsSemanticDiagnostics(), ...p.getNgSemanticDiagnostics()];
-    if (diags.length > 0) {
-      console.error('Diagnostics: ' + ng.formatDiagnostics(options, diags));
-      throw new Error('Expected no diagnostics.');
-    }
-  }
-
   beforeEach(() => {
     errorSpy = jasmine.createSpy('consoleError').and.callFake(console.error);
-    basePath = makeTempDir();
-    write = (fileName: string, content: string) => {
-      const dir = path.dirname(fileName);
-      if (dir != '.') {
-        const newDir = path.join(basePath, dir);
-        if (!fs.existsSync(newDir)) fs.mkdirSync(newDir);
-      }
-      fs.writeFileSync(path.join(basePath, fileName), content, {encoding: 'utf-8'});
-    };
-    const ngRootDir = getNgRootDir();
-    const nodeModulesPath = path.resolve(basePath, 'node_modules');
-    fs.mkdirSync(nodeModulesPath);
-    fs.symlinkSync(
-        path.resolve(ngRootDir, 'dist', 'all', '@angular'),
-        path.resolve(nodeModulesPath, '@angular'));
-    fs.symlinkSync(
-        path.resolve(ngRootDir, 'node_modules', 'rxjs'), path.resolve(nodeModulesPath, 'rxjs'));
-    fs.symlinkSync(
-        path.resolve(ngRootDir, 'node_modules', 'typescript'),
-        path.resolve(nodeModulesPath, 'typescript'));
+    testSupport = setup();
   });
 
-  describe('reuse of old ts program', () => {
-    const files = {
-      'src/util.ts': `export const x = 1;`,
-      'src/main.ts': `
-        import {NgModule, Component} from '@angular/core';
-        import {x} from './util';
+  function createModuleAndCompSource(prefix: string, template: string = prefix + 'template') {
+    const templateEntry =
+        template.endsWith('.html') ? `templateUrl: '${template}'` : `template: \`${template}\``;
+    return `
+      import {Component, NgModule} from '@angular/core';
 
-        @Component({selector: 'comp', templateUrl: './main.html'})
-        export class MyComp {}
+      @Component({selector: '${prefix}', ${templateEntry}})
+      export class ${prefix}Comp {}
 
-        @NgModule()
-        export class MyModule {}
-      `,
-      'src/main.html': `Hello world`,
-    };
+      @NgModule({declarations: [${prefix}Comp]})
+      export class ${prefix}Module {}
+    `;
+  }
 
-    function expectResuse(newFiles: {[fileName: string]: string}, reuseLevel: StructureIsReused) {
-      writeFiles(files);
+  describe('reuse of old program', () => {
 
-      const options1 = createCompilerOptions();
-      const host1 = ng.createCompilerHost({options: options1});
-      const rootNames1 = [path.resolve(basePath, 'src/main.ts')];
-
-      const p1 = ng.createProgram({rootNames: rootNames1, options: options1, host: host1});
-      expectNoDiagnostics(options1, p1);
-
-      // Note: we recreate the options, rootNames and the host
-      // to check that TS checks against values, and not references!
-      writeFiles(newFiles);
-      const options2 = {...options1};
-      const host2 = ng.createCompilerHost({options: options2});
-      const rootNames2 = [...rootNames1];
-
-      const p2 =
-          ng.createProgram({rootNames: rootNames2, options: options2, host: host2, oldProgram: p1});
-      expectNoDiagnostics(options1, p2);
-
-      expect(tsStructureIsReused(p1.getTsProgram())).toBe(reuseLevel);
+    function compileLib(libName: string) {
+      testSupport.writeFiles({
+        [`${libName}_src/index.ts`]: createModuleAndCompSource(libName),
+      });
+      const options = testSupport.createCompilerOptions({
+        skipTemplateCodegen: true,
+      });
+      const program = ng.createProgram({
+        rootNames: [path.resolve(testSupport.basePath, `${libName}_src/index.ts`)],
+        options,
+        host: ng.createCompilerHost({options}),
+      });
+      expectNoDiagnosticsInProgram(options, program);
+      fs.symlinkSync(
+          path.resolve(testSupport.basePath, 'built', `${libName}_src`),
+          path.resolve(testSupport.basePath, 'node_modules', libName));
+      program.emit({emitFlags: ng.EmitFlags.DTS | ng.EmitFlags.JS | ng.EmitFlags.Metadata});
     }
 
-    it('should reuse completely if nothing changed',
-       () => { expectResuse({}, StructureIsReused.Completely); });
+    function compile(oldProgram?: ng.Program): ng.Program {
+      const options = testSupport.createCompilerOptions();
+      const rootNames = [path.resolve(testSupport.basePath, 'src/index.ts')];
 
-    it('should resuse if a template or a ts file changed', () => {
-      expectResuse(
-          {
-            'src/main.html': `Some other text`,
-            'src/util.ts': `export const x = 2;`,
-          },
-          StructureIsReused.Completely);
+      const program = ng.createProgram({
+        rootNames: rootNames,
+        options: testSupport.createCompilerOptions(),
+        host: ng.createCompilerHost({options}), oldProgram,
+      });
+      expectNoDiagnosticsInProgram(options, program);
+      program.emit();
+      return program;
+    }
+
+    it('should reuse generated code for libraries from old programs', () => {
+      compileLib('lib');
+      testSupport.writeFiles({
+        'src/main.ts': createModuleAndCompSource('main'),
+        'src/index.ts': `
+            export * from './main';
+            export * from 'lib/index';
+          `
+      });
+      const p1 = compile();
+      expect(p1.getTsProgram().getSourceFiles().some(
+                 sf => /node_modules\/lib\/.*\.ngfactory\.ts$/.test(sf.fileName)))
+          .toBe(true);
+      expect(p1.getTsProgram().getSourceFiles().some(
+                 sf => /node_modules\/lib2\/.*\.ngfactory.*$/.test(sf.fileName)))
+          .toBe(false);
+      const p2 = compile(p1);
+      expect(p2.getTsProgram().getSourceFiles().some(
+                 sf => /node_modules\/lib\/.*\.ngfactory.*$/.test(sf.fileName)))
+          .toBe(false);
+      expect(p2.getTsProgram().getSourceFiles().some(
+                 sf => /node_modules\/lib2\/.*\.ngfactory.*$/.test(sf.fileName)))
+          .toBe(false);
+
+      // import a library for which we didn't generate code before
+      compileLib('lib2');
+      testSupport.writeFiles({
+        'src/index.ts': `
+          export * from './main';
+          export * from 'lib/index';
+          export * from 'lib2/index';
+        `,
+      });
+      const p3 = compile(p2);
+      expect(p3.getTsProgram().getSourceFiles().some(
+                 sf => /node_modules\/lib\/.*\.ngfactory.*$/.test(sf.fileName)))
+          .toBe(false);
+      expect(p3.getTsProgram().getSourceFiles().some(
+                 sf => /node_modules\/lib2\/.*\.ngfactory\.ts$/.test(sf.fileName)))
+          .toBe(true);
+
+      const p4 = compile(p3);
+      expect(p4.getTsProgram().getSourceFiles().some(
+                 sf => /node_modules\/lib\/.*\.ngfactory.*$/.test(sf.fileName)))
+          .toBe(false);
+      expect(p4.getTsProgram().getSourceFiles().some(
+                 sf => /node_modules\/lib2\/.*\.ngfactory.*$/.test(sf.fileName)))
+          .toBe(false);
     });
 
-    it('should not reuse if an import changed', () => {
-      expectResuse(
-          {
-            'src/util.ts': `
-          import {Injectable} from '@angular/core';
-          export const x = 2;
-        `,
-          },
-          StructureIsReused.SafeModules);
+    it('should reuse the old ts program completely if nothing changed', () => {
+      testSupport.writeFiles({'src/index.ts': createModuleAndCompSource('main')});
+      // Note: the second compile drops factories for library files,
+      // and therefore changes the structure again
+      const p1 = compile();
+      const p2 = compile(p1);
+      const p3 = compile(p2);
+      expect(tsStructureIsReused(p2.getTsProgram())).toBe(StructureIsReused.Completely);
+    });
+
+    it('should reuse the old ts program completely if a template or a ts file changed', () => {
+      testSupport.writeFiles({
+        'src/main.ts': createModuleAndCompSource('main', 'main.html'),
+        'src/main.html': `Some template`,
+        'src/util.ts': `export const x = 1`,
+        'src/index.ts': `
+          export * from './main';
+          export * from './util';
+        `
+      });
+      // Note: the second compile drops factories for library files,
+      // and therefore changes the structure again
+      const p1 = compile();
+      const p2 = compile(p1);
+      testSupport.writeFiles({
+        'src/main.html': `Another template`,
+        'src/util.ts': `export const x = 2`,
+      });
+      const p3 = compile(p2);
+      expect(tsStructureIsReused(p2.getTsProgram())).toBe(StructureIsReused.Completely);
+    });
+
+    it('should not reuse the old ts program if an import changed', () => {
+      testSupport.writeFiles({
+        'src/main.ts': createModuleAndCompSource('main'),
+        'src/util.ts': `export const x = 1`,
+        'src/index.ts': `
+          export * from './main';
+          export * from './util';
+        `
+      });
+      // Note: the second compile drops factories for library files,
+      // and therefore changes the structure again
+      const p1 = compile();
+      const p2 = compile(p1);
+      testSupport.writeFiles(
+          {'src/util.ts': `import {Injectable} from '@angular/core'; export const x = 1;`});
+      const p3 = compile(p2);
+      expect(tsStructureIsReused(p2.getTsProgram())).toBe(StructureIsReused.SafeModules);
     });
   });
 
   it('should typecheck templates even if skipTemplateCodegen is set', () => {
-    writeFiles({
-      'src/main.ts': `
-        import {NgModule, Component} from '@angular/core';
-
-        @Component({selector: 'mycomp', template: '{{nonExistent}}'})
-        export class MyComp {}
-
-        @NgModule({declarations: [MyComp]})
-        export class MyModule {}
-      `
+    testSupport.writeFiles({
+      'src/main.ts': createModuleAndCompSource('main', `{{nonExistent}}`),
     });
-    const options = createCompilerOptions({skipTemplateCodegen: true});
+    const options = testSupport.createCompilerOptions({skipTemplateCodegen: true});
     const host = ng.createCompilerHost({options});
-    const program =
-        ng.createProgram({rootNames: [path.resolve(basePath, 'src/main.ts')], options, host});
+    const program = ng.createProgram(
+        {rootNames: [path.resolve(testSupport.basePath, 'src/main.ts')], options, host});
     const diags = program.getNgSemanticDiagnostics();
     expect(diags.length).toBe(1);
-    expect(diags[0].messageText).toBe(`Property 'nonExistent' does not exist on type 'MyComp'.`);
+    expect(diags[0].messageText).toBe(`Property 'nonExistent' does not exist on type 'mainComp'.`);
   });
 
   it('should be able to use asynchronously loaded resources', (done) => {
-    writeFiles({
-      'src/main.ts': `
-        import {NgModule, Component} from '@angular/core';
-
-        @Component({selector: 'mycomp', templateUrl: './main.html'})
-        export class MyComp {}
-
-        @NgModule({declarations: [MyComp]})
-        export class MyModule {}
-      `,
+    testSupport.writeFiles({
+      'src/main.ts': createModuleAndCompSource('main', 'main.html'),
       // Note: we need to be able to resolve the template synchronously,
       // only the content is delivered asynchronously.
       'src/main.html': '',
     });
-    const options = createCompilerOptions();
+    const options = testSupport.createCompilerOptions();
     const host = ng.createCompilerHost({options});
     host.readResource = () => Promise.resolve('Hello world!');
-    const program =
-        ng.createProgram({rootNames: [path.resolve(basePath, 'src/main.ts')], options, host});
+    const program = ng.createProgram(
+        {rootNames: [path.resolve(testSupport.basePath, 'src/main.ts')], options, host});
     program.loadNgStructureAsync().then(() => {
       program.emit();
-      const factory = fs.readFileSync(path.resolve(basePath, 'built/src/main.ngfactory.js'));
+      const factory =
+          fs.readFileSync(path.resolve(testSupport.basePath, 'built/src/main.ngfactory.js'));
       expect(factory).toContain('Hello world!');
       done();
     });
   });
 });
-
-function appComponentSource(): string {
-  return `
-    import {Component, Pipe, Directive} from '@angular/core';
-
-    export interface Person {
-      name: string;
-      address: Address;
-    }
-
-    export interface Address {
-      street: string;
-      city: string;
-      state: string;
-      zip: string;
-    }
-
-    @Component({
-      templateUrl: './app.component.html'
-    })
-    export class AppComponent {
-      name = 'Angular';
-      person: Person;
-      people: Person[];
-      maybePerson?: Person;
-
-      getName(): string { return this.name; }
-      getPerson(): Person { return this.person; }
-      getMaybePerson(): Person | undefined { return this.maybePerson; }
-    }
-
-    @Pipe({
-      name: 'aPipe',
-    })
-    export class APipe {
-      transform(n: number): number { return n + 1; }
-    }
-
-    @Directive({
-      selector: '[aDir]',
-      exportAs: 'aDir'
-    })
-    export class ADirective {
-      name = 'ADirective';
-    }
-  `;
-}
-
-const QUICKSTART = {
-  'src/app.component.ts': appComponentSource(),
-  'src/app.component.html': '<h1>Hello {{name}}</h1>',
-  'src/app.module.ts': `
-    import { NgModule }      from '@angular/core';
-    import { AppComponent, APipe, ADirective }  from './app.component';
-
-    @NgModule({
-      declarations: [ AppComponent, APipe, ADirective ],
-      bootstrap:    [ AppComponent ]
-    })
-    export class AppModule { }
-  `
-};
-
-const LOWERING_QUICKSTART = {
-  'src/app.component.ts': appComponentSource(),
-  'src/app.component.html': '<h1>Hello {{name}}</h1>',
-  'src/app.module.ts': `
-    import { NgModule, Component }      from '@angular/core';
-
-    import { AppComponent, APipe, ADirective }  from './app.component';
-
-    class Foo {}
-
-    @Component({
-      template: '',
-      providers: [
-        {provide: 'someToken', useFactory: () => new Foo()}
-      ]
-    })
-    export class Bar {}
-
-    @NgModule({
-      declarations: [ AppComponent, APipe, ADirective, Bar ],
-      bootstrap:    [ AppComponent ]
-    })
-    export class AppModule { }
-  `
-};
-
-function expectNoDiagnostics(diagnostics: ng.Diagnostics) {
-  if (diagnostics && diagnostics.length) {
-    throw new Error(ng.formatDiagnostics({}, diagnostics));
-  }
-}