Refactor production serializers to use directly the graph information

Reviewed By: mjesun

Differential Revision: D7158632

fbshipit-source-id: 91fad2e3ca617ea5f3b283e335c0d70edbb6ff3b

packages/metro-minify-uglify/src/minifier.js

@@ -34,7 +34,7 @@ function withSourceMap(
 
 function minify(inputCode: string, inputMap: ?BabelSourceMap) {
   const result = uglify.minify(inputCode, {
-    mangle: {toplevel: true},
+    mangle: {toplevel: false},
     output: {
       ascii_only: true,
       quote_style: 3,
@@ -44,7 +44,7 @@ function minify(inputCode: string, inputMap: ?BabelSourceMap) {
       content: inputMap,
       includeSources: false,
     },
-    toplevel: true,
+    toplevel: false,
     compress: {
       // reduce_funcs inlines single-use function, which cause perf regressions.
       reduce_funcs: false,

packages/metro/src/DeltaBundler/DeltaTransformer.js

@@ -444,7 +444,7 @@ class DeltaTransformer extends EventEmitter {
     const name = this._dependencyGraph.getHasteName(edge.path);
 
     const wrappedCode = wrapModule(edge, {
-      createModuleIdFn: this._getModuleId,
+      createModuleId: this._getModuleId,
       dev: transformOptions.dev,
     });
 

packages/metro/src/DeltaBundler/Serializers/__tests__/plainJSBundle-test.js

@@ -42,7 +42,7 @@ it('should serialize a very simple bundle', () => {
         entryPoints: ['foo'],
       },
       {
-        createModuleIdFn: path => path,
+        createModuleId: path => path,
         dev: true,
         runBeforeMainModule: [],
         runModule: true,
@@ -70,7 +70,7 @@ it('should add runBeforeMainModule statements if found in the graph', () => {
         entryPoints: ['foo'],
       },
       {
-        createModuleIdFn: path => path,
+        createModuleId: path => path,
         dev: true,
         runBeforeMainModule: ['bar', 'non-existant'],
         runModule: true,
@@ -99,7 +99,7 @@ it('should handle numeric module ids', () => {
         entryPoints: ['foo'],
       },
       {
-        createModuleIdFn: createModuleIdFactory(),
+        createModuleId: createModuleIdFactory(),
         dev: true,
         runBeforeMainModule: ['bar', 'non-existant'],
         runModule: true,

packages/metro/src/DeltaBundler/Serializers/helpers/__tests__/js-test.js

@@ -35,7 +35,7 @@ describe('wrapModule()', () => {
   it('Should wrap a module in nondev mode', () => {
     expect(
       wrapModule(myModule, {
-        createModuleIdFn: createModuleIdFactory(),
+        createModuleId: createModuleIdFactory(),
         dev: false,
       }),
     ).toEqual('__d(function() { console.log("foo") },0,[1,2]);');
@@ -44,7 +44,7 @@ describe('wrapModule()', () => {
   it('Should wrap a module in dev mode', () => {
     expect(
       wrapModule(myModule, {
-        createModuleIdFn: createModuleIdFactory(),
+        createModuleId: createModuleIdFactory(),
         dev: true,
       }),
     ).toEqual('__d(function() { console.log("foo") },0,[1,2],"foo.js");');
@@ -55,17 +55,17 @@ describe('wrapModule()', () => {
 
     expect(
       wrapModule(myModule, {
-        createModuleIdFn: createModuleIdFactory(),
+        createModuleId: createModuleIdFactory(),
         dev: true,
       }),
     ).toEqual(myModule.output.code);
   });
 
-  it('should use custom createModuleIdFn param', () => {
-    // Just use a createModuleIdFn that returns the same path.
+  it('should use custom createModuleId param', () => {
+    // Just use a createModuleId that returns the same path.
     expect(
       wrapModule(myModule, {
-        createModuleIdFn: path => path,
+        createModuleId: path => path,
         dev: false,
       }),
     ).toEqual(

packages/metro/src/DeltaBundler/Serializers/helpers/js.js

@@ -16,7 +16,7 @@ const path = require('path');
 import type {DependencyEdge} from '../../traverseDependencies';
 
 export type Options = {
-  +createModuleIdFn: string => number | string,
+  +createModuleId: string => number | string,
   +dev: boolean,
 };
 
@@ -25,10 +25,10 @@ function wrapModule(module: DependencyEdge, options: Options) {
     return module.output.code;
   }
 
-  const moduleId = options.createModuleIdFn(module.path);
+  const moduleId = options.createModuleId(module.path);
   const params = [
     moduleId,
-    Array.from(module.dependencies.values()).map(options.createModuleIdFn),
+    Array.from(module.dependencies.values()).map(options.createModuleId),
   ];
 
   // Add the module name as the last parameter (to make it easier to do

packages/metro/src/DeltaBundler/Serializers/plainJSBundle.js

@@ -10,13 +10,15 @@
 
 'use strict';
 
+const getAppendScripts = require('../../lib/getAppendScripts');
+
 const {wrapModule} = require('./helpers/js');
 
 import type {Graph} from '../DeltaCalculator';
 import type {DependencyEdge} from '../traverseDependencies';
 
 type Options = {|
-  createModuleIdFn: string => number | string,
+  createModuleId: string => number | string,
   +dev: boolean,
   +runBeforeMainModule: $ReadOnlyArray<string>,
   +runModule: boolean,
@@ -29,35 +31,17 @@ function plainJSBundle(
   graph: Graph,
   options: Options,
 ): string {
-  const output = [];
-
-  for (const module of pre) {
-    output.push(wrapModule(module, options));
-  }
-
   for (const module of graph.dependencies.values()) {
-    output.push(wrapModule(module, options));
+    options.createModuleId(module.path);
   }
 
-  for (const path of options.runBeforeMainModule) {
-    if (graph.dependencies.has(path)) {
-      output.push(
-        `require(${JSON.stringify(options.createModuleIdFn(path))});`,
-      );
-    }
-  }
-
-  if (options.runModule && graph.dependencies.has(entryPoint)) {
-    output.push(
-      `require(${JSON.stringify(options.createModuleIdFn(entryPoint))});`,
-    );
-  }
-
-  if (options.sourceMapUrl) {
-    output.push(`//# sourceMappingURL=${options.sourceMapUrl}`);
-  }
-
-  return output.join('\n');
+  return [
+    ...pre,
+    ...graph.dependencies.values(),
+    ...getAppendScripts(entryPoint, graph, options),
+  ]
+    .map(module => wrapModule(module, options))
+    .join('\n');
 }
 
 module.exports = plainJSBundle;

packages/metro/src/DeltaBundler/index.js

@@ -10,10 +10,16 @@
 
 'use strict';
 
+const DeltaCalculator = require('./DeltaCalculator');
 const DeltaTransformer = require('./DeltaTransformer');
 
 import type Bundler from '../Bundler';
 import type {BundleOptions} from '../shared/types.flow';
+import type {
+  DeltaResult,
+  Graph as CalculatorGraph,
+  Options,
+} from './DeltaCalculator';
 import type {DeltaEntry} from './DeltaTransformer';
 
 export type PostProcessModules = (
@@ -27,6 +33,9 @@ export type MainOptions = {|
   postProcessModules?: PostProcessModules,
 |};
 
+export type Delta = DeltaResult;
+export type Graph = CalculatorGraph;
+
 /**
  * `DeltaBundler` uses the `DeltaTransformer` to build bundle deltas. This
  * module handles all the transformer instances so it can support multiple
@@ -38,6 +47,7 @@ class DeltaBundler {
   _options: MainOptions;
   _deltaTransformers: Map<string, DeltaTransformer> = new Map();
   _currentId: number = 0;
+  _deltaCalculators: Map<Graph, DeltaCalculator> = new Map();
 
   constructor(bundler: Bundler, options: MainOptions) {
     this._bundler = bundler;
@@ -47,6 +57,9 @@ class DeltaBundler {
   end() {
     this._deltaTransformers.forEach(DeltaTransformer => DeltaTransformer.end());
     this._deltaTransformers = new Map();
+
+    this._deltaCalculators.forEach(deltaCalculator => deltaCalculator.end());
+    this._deltaCalculators = new Map();
   }
 
   endTransformer(clientId: string) {
@@ -78,6 +91,55 @@ class DeltaBundler {
     return deltaTransformer;
   }
 
+  async buildGraph(options: Options): Promise<Graph> {
+    const depGraph = await this._bundler.getDependencyGraph();
+
+    const deltaCalculator = new DeltaCalculator(
+      this._bundler,
+      depGraph,
+      options,
+    );
+
+    await deltaCalculator.getDelta({reset: true});
+    const graph = deltaCalculator.getGraph();
+
+    this._deltaCalculators.set(graph, deltaCalculator);
+
+    return graph;
+  }
+
+  async getDelta(graph: Graph, {reset}: {reset: boolean}): Promise<Delta> {
+    const deltaCalculator = this._deltaCalculators.get(graph);
+
+    if (!deltaCalculator) {
+      throw new Error('Graph not found');
+    }
+
+    return await deltaCalculator.getDelta({reset});
+  }
+
+  listen(graph: Graph, callback: () => mixed) {
+    const deltaCalculator = this._deltaCalculators.get(graph);
+
+    if (!deltaCalculator) {
+      throw new Error('Graph not found');
+    }
+
+    deltaCalculator.on('change', callback);
+  }
+
+  endGraph(graph: Graph) {
+    const deltaCalculator = this._deltaCalculators.get(graph);
+
+    if (!deltaCalculator) {
+      throw new Error('Graph not found');
+    }
+
+    deltaCalculator.end();
+
+    this._deltaCalculators.delete(graph);
+  }
+
   getPostProcessModulesFn(
     entryPoint: string,
   ): (modules: $ReadOnlyArray<DeltaEntry>) => $ReadOnlyArray<DeltaEntry> {

packages/metro/src/Server/__tests__/Server-test.js

@@ -19,6 +19,7 @@ jest
   }))
   .mock('../../Bundler')
   .mock('../../Assets')
+  .mock('../../lib/getPrependedScripts')
   .mock('../../node-haste/DependencyGraph')
   .mock('metro-core/src/Logger')
   .mock('../../lib/getAbsolutePath')
@@ -29,6 +30,7 @@ describe('processRequest', () => {
   let Bundler;
   let Server;
   let getAsset;
+  let getPrependedScripts;
   let symbolicate;
   let Serializers;
   let DeltaBundler;
@@ -40,6 +42,7 @@ describe('processRequest', () => {
     Bundler = require('../../Bundler');
     Server = require('../');
     getAsset = require('../../Assets').getAsset;
+    getPrependedScripts = require('../../lib/getPrependedScripts');
     symbolicate = require('../symbolicate/symbolicate');
     Serializers = require('../../DeltaBundler/Serializers/Serializers');
     DeltaBundler = require('../../DeltaBundler');
@@ -85,6 +88,15 @@ describe('processRequest', () => {
   let requestHandler;
 
   beforeEach(() => {
+    DeltaBundler.prototype.buildGraph = jest.fn().mockReturnValue(
+      Promise.resolve({
+        entryPoints: [''],
+        dependencies: new Map(),
+      }),
+    );
+
+    getPrependedScripts.mockReturnValue(Promise.resolve([]));
+
     Serializers.fullBundle.mockReturnValue(
       Promise.resolve({
         bundle: 'this is the source',
@@ -445,28 +457,16 @@ describe('processRequest', () => {
           entryFile: 'foo file',
         })
         .then(() =>
-          expect(Serializers.fullBundle).toBeCalledWith(
-            expect.any(DeltaBundler),
-            {
-              assetPlugins: [],
-              customTransformOptions: {},
-              dev: true,
-              entryFile: '/root/foo file',
-              entryModuleOnly: false,
-              excludeSource: false,
-              hot: false,
-              inlineSourceMap: false,
-              isolateModuleIDs: false,
-              minify: false,
-              onProgress: null,
-              platform: undefined,
-              resolutionResponse: null,
-              runBeforeMainModule: ['InitializeCore'],
-              runModule: true,
-              sourceMapUrl: null,
-              unbundle: false,
-            },
-          ),
+          expect(DeltaBundler.prototype.buildGraph).toBeCalledWith({
+            assetPlugins: [],
+            customTransformOptions: {},
+            dev: true,
+            entryPoints: ['/root/foo file'],
+            hot: false,
+            minify: false,
+            onProgress: null,
+            platform: undefined,
+          }),
         );
     });
   });

packages/metro/src/Server/index.js

@@ -14,13 +14,19 @@ const Bundler = require('../Bundler');
 const DeltaBundler = require('../DeltaBundler');
 const MultipartResponse = require('./MultipartResponse');
 const Serializers = require('../DeltaBundler/Serializers/Serializers');
+
+const defaultCreateModuleIdFactory = require('../lib/createModuleIdFactory');
+const plainJSBundle = require('../DeltaBundler/Serializers/plainJSBundle');
+const sourceMapString = require('../DeltaBundler/Serializers/sourceMapString');
 const debug = require('debug')('Metro:Server');
 const defaults = require('../defaults');
 const formatBundlingError = require('../lib/formatBundlingError');
 const getAbsolutePath = require('../lib/getAbsolutePath');
 const getMaxWorkers = require('../lib/getMaxWorkers');
 const getOrderedDependencyPaths = require('../lib/getOrderedDependencyPaths');
+const getPrependedScripts = require('../lib/getPrependedScripts');
 const mime = require('mime-types');
+const mapGraph = require('../lib/mapGraph');
 const nullthrows = require('fbjs/lib/nullthrows');
 const parseCustomTransformOptions = require('../lib/parseCustomTransformOptions');
 const parsePlatformFilePath = require('../node-haste/lib/parsePlatformFilePath');
@@ -32,6 +38,7 @@ const {getAsset} = require('../Assets');
 const resolveSync: ResolveSync = require('resolve').sync;
 
 import type {CustomError} from '../lib/formatBundlingError';
+import type {DependencyEdge} from '../DeltaBundler/traverseDependencies';
 import type {IncomingMessage, ServerResponse} from 'http';
 import type {Reporter} from '../lib/reporting';
 import type {
@@ -73,7 +80,7 @@ class Server {
     blacklistRE: void | RegExp,
     cacheStores: $ReadOnlyArray<CacheStore<TransformedCode>>,
     cacheVersion: string,
-    createModuleIdFactory?: () => (path: string) => number,
+    createModuleId: (path: string) => number,
     enableBabelRCLookup: boolean,
     extraNodeModules: {},
     getPolyfills: ({platform: ?string}) => $ReadOnlyArray<string>,
@@ -119,6 +126,9 @@ class Server {
     const assetExts = options.assetExts || defaults.assetExts;
     const sourceExts = options.sourceExts || defaults.sourceExts;
 
+    const _createModuleId =
+      options.createModuleId || defaultCreateModuleIdFactory();
+
     this._opts = {
       assetExts: options.assetTransforms ? [] : assetExts,
       assetRegistryPath: options.assetRegistryPath,
@@ -126,7 +136,7 @@ class Server {
       cacheStores: options.cacheStores,
       cacheVersion: options.cacheVersion,
       dynamicDepsInPackages: options.dynamicDepsInPackages || 'throwAtRuntime',
-      createModuleIdFactory: options.createModuleIdFactory,
+      createModuleId: _createModuleId,
       enableBabelRCLookup:
         options.enableBabelRCLookup != null
           ? options.enableBabelRCLookup
@@ -175,7 +185,7 @@ class Server {
     // This slices out options that are not part of the strict BundlerOptions
     /* eslint-disable no-unused-vars */
     const {
-      createModuleIdFactory,
+      createModuleId,
       getModulesRunBeforeMainModule,
       moduleFormat,
       silent,
@@ -230,27 +240,48 @@ class Server {
   }
 
   async build(options: BundleOptions): Promise<{code: string, map: string}> {
-    options = {
-      ...options,
-      runBeforeMainModule: this._opts.getModulesRunBeforeMainModule(
-        options.entryFile,
-      ),
-      entryFile: getAbsolutePath(options.entryFile, this._opts.projectRoots),
-    };
-
-    const fullBundle = await Serializers.fullBundle(
-      this._deltaBundler,
-      options,
+    const entryPoint = getAbsolutePath(
+      options.entryFile,
+      this._opts.projectRoots,
     );
 
-    const fullMap = await Serializers.fullSourceMap(
-      this._deltaBundler,
+    let graph = await this._deltaBundler.buildGraph({
+      assetPlugins: options.assetPlugins,
+      customTransformOptions: options.customTransformOptions,
+      dev: options.dev,
+      entryPoints: [entryPoint],
+      hot: options.hot,
+      minify: options.minify,
+      onProgress: options.onProgress,
+      platform: options.platform,
+    });
+    let prependScripts = await getPrependedScripts(
+      this._opts,
       options,
+      this._bundler,
     );
 
+    if (options.minify) {
+      prependScripts = await Promise.all(
+        prependScripts.map(script => this._minifyModule(script)),
+      );
+
+      graph = await mapGraph(graph, module => this._minifyModule(module));
+    }
+
     return {
-      code: fullBundle.bundle,
-      map: fullMap,
+      code: plainJSBundle(entryPoint, prependScripts, graph, {
+        createModuleId: this._opts.createModuleId,
+        dev: options.dev,
+        runBeforeMainModule: this._opts.getModulesRunBeforeMainModule(
+          options.entryFile,
+        ),
+        runModule: options.runModule,
+        sourceMapUrl: options.sourceMapUrl,
+      }),
+      map: sourceMapString(prependScripts, graph, {
+        excludeSource: options.excludeSource,
+      }),
     };
   }
 
@@ -299,6 +330,24 @@ class Server {
     return await getOrderedDependencyPaths(this._deltaBundler, bundleOptions);
   }
 
+  async _minifyModule(module: DependencyEdge): Promise<DependencyEdge> {
+    const {code, map} = await this._bundler.minifyModule(
+      module.path,
+      module.output.code,
+      module.output.map,
+    );
+
+    // $FlowIssue #16581373 spread of an exact object should be exact
+    return {
+      ...module,
+      output: {
+        ...module.output,
+        code,
+        map,
+      },
+    };
+  }
+
   onFileChange(type: string, filePath: string) {
     Promise.all(
       this._fileChangeListeners.map(listener => listener(filePath)),

packages/metro/src/integration_tests/__tests__/__snapshots__/basic_bundle-test.js.snap

@@ -149,7 +149,7 @@ __d(function (global, _require, module, exports, _dependencyMap) {
     Foo: Foo,
     Bar: Bar
   };
-},4,[5,6]);
+},0,[1,2]);
 __d(function (global, _require, module, exports, _dependencyMap) {
   'use strict';
 
@@ -159,7 +159,7 @@ __d(function (global, _require, module, exports, _dependencyMap) {
     type: 'bar',
     foo: Foo.type
   };
-},5,[6]);
+},1,[2]);
 __d(function (global, _require, module, exports, _dependencyMap) {
   'use strict';
 
@@ -169,7 +169,7 @@ __d(function (global, _require, module, exports, _dependencyMap) {
     type: 'foo',
     asset: asset
   };
-},6,[7]);
+},2,[3]);
 __d(function (global, _require, module, exports, _dependencyMap) {
   module.exports = _require(_dependencyMap[0]).registerAsset({
     \\"__packager_asset\\": true,
@@ -181,11 +181,11 @@ __d(function (global, _require, module, exports, _dependencyMap) {
     \\"name\\": \\"test\\",
     \\"type\\": \\"png\\"
   });
-},7,[8]);
+},3,[4]);
 __d(function (global, _require, module, exports, _dependencyMap) {
   'use strict';
-},8,[]);
-require(4);"
+},4,[]);
+require(0);"
 `;
 
 exports[`basic_bundle bundles package without polyfills 1`] = `
@@ -323,7 +323,7 @@ __d(function (global, _require, module, exports, _dependencyMap) {
     Foo: Foo,
     Bar: Bar
   };
-},2,[3,4]);
+},0,[1,2]);
 __d(function (global, _require, module, exports, _dependencyMap) {
   'use strict';
 
@@ -333,7 +333,7 @@ __d(function (global, _require, module, exports, _dependencyMap) {
     type: 'bar',
     foo: Foo.type
   };
-},3,[4]);
+},1,[2]);
 __d(function (global, _require, module, exports, _dependencyMap) {
   'use strict';
 
@@ -343,7 +343,7 @@ __d(function (global, _require, module, exports, _dependencyMap) {
     type: 'foo',
     asset: asset
   };
-},4,[5]);
+},2,[3]);
 __d(function (global, _require, module, exports, _dependencyMap) {
   module.exports = _require(_dependencyMap[0]).registerAsset({
     \\"__packager_asset\\": true,
@@ -355,9 +355,9 @@ __d(function (global, _require, module, exports, _dependencyMap) {
     \\"name\\": \\"test\\",
     \\"type\\": \\"png\\"
   });
-},5,[6]);
+},3,[4]);
 __d(function (global, _require, module, exports, _dependencyMap) {
   'use strict';
-},6,[]);
-require(2);"
+},4,[]);
+require(0);"
 `;

packages/metro/src/lib/__tests__/mapGraph-test.js

@@ -0,0 +1,58 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails oncall+javascript_foundation
+ * @format
+ */
+
+'use strict';
+
+const mapGraph = require('../mapGraph');
+
+let graph;
+
+beforeEach(() => {
+  graph = {
+    dependencies: new Map([
+      ['/entryPoint', {name: 'entryPoint', id: '1'}],
+      ['/foo', {name: 'foo', id: '2'}],
+      ['/baz', {name: 'baz', id: '3'}],
+    ]),
+    entryPoints: ['/entryPoint'],
+  };
+});
+
+it('should map the passed graph when a sync function is passed', async () => {
+  const mapped = await mapGraph(graph, element => ({
+    name: '-' + element.name + '-',
+    id: parseInt(element.id, 10),
+  }));
+
+  expect(mapped.dependencies).toEqual(
+    new Map([
+      ['/entryPoint', {name: '-entryPoint-', id: 1}],
+      ['/foo', {name: '-foo-', id: 2}],
+      ['/baz', {name: '-baz-', id: 3}],
+    ]),
+  );
+  expect(mapped.entryPoints).toEqual(['/entryPoint']);
+});
+
+it('should map the passed graph when an async function is passed', async () => {
+  const mapped = await mapGraph(graph, async element => ({
+    name: '-' + element.name + '-',
+    id: parseInt(element.id, 10),
+  }));
+
+  expect(mapped.dependencies).toEqual(
+    new Map([
+      ['/entryPoint', {name: '-entryPoint-', id: 1}],
+      ['/foo', {name: '-foo-', id: 2}],
+      ['/baz', {name: '-baz-', id: 3}],
+    ]),
+  );
+  expect(mapped.entryPoints).toEqual(['/entryPoint']);
+});

packages/metro/src/lib/getAppendScripts.js

@@ -0,0 +1,67 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ * @format
+ */
+
+'use strict';
+
+import type {Graph} from '../DeltaBundler/DeltaCalculator';
+import type {DependencyEdge} from '../DeltaBundler/traverseDependencies';
+
+type Options = {
+  +createModuleId: string => number | string,
+  +runBeforeMainModule: $ReadOnlyArray<string>,
+  +runModule: boolean,
+  +sourceMapUrl: ?string,
+};
+
+function getAppendScripts(
+  entryPoint: string,
+  graph: Graph,
+  options: Options,
+): $ReadOnlyArray<DependencyEdge> {
+  const output = [];
+
+  if (options.runModule) {
+    const paths = [...options.runBeforeMainModule, entryPoint];
+
+    for (const path of paths) {
+      if (graph.dependencies.has(path)) {
+        output.push({
+          path: `require-${path}`,
+          dependencies: new Map(),
+          inverseDependencies: new Set(),
+          output: {
+            code: `require(${JSON.stringify(options.createModuleId(path))});`,
+            source: '',
+            map: [],
+            type: 'script',
+          },
+        });
+      }
+    }
+  }
+
+  if (options.sourceMapUrl) {
+    output.push({
+      path: 'source-map',
+      dependencies: new Map(),
+      inverseDependencies: new Set(),
+      output: {
+        code: `//# sourceMappingURL=${options.sourceMapUrl}`,
+        source: '',
+        map: [],
+        type: 'script',
+      },
+    });
+  }
+
+  return output;
+}
+
+module.exports = getAppendScripts;

packages/metro/src/lib/getPrependedScripts.js

@@ -0,0 +1,125 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ * @format
+ */
+
+'use strict';
+
+const defaults = require('../defaults');
+const getPreludeCode = require('./getPreludeCode');
+
+import type Bundler from '../Bundler';
+import type {DependencyEdge} from '../DeltaBundler/traverseDependencies';
+import type Module from '../node-haste/Module';
+
+type Options = {
+  enableBabelRCLookup: boolean,
+  getPolyfills: ({platform: ?string}) => $ReadOnlyArray<string>,
+  polyfillModuleNames: Array<string>,
+  projectRoots: $ReadOnlyArray<string>,
+};
+
+type BundleOptions = {
+  +dev: boolean,
+  +hot: boolean,
+  +platform: ?string,
+};
+
+async function getPrependedScripts(
+  options: Options,
+  bundleOptions: BundleOptions,
+  bundler: Bundler,
+): Promise<Array<DependencyEdge>> {
+  // Get all the polyfills from the relevant option params (the
+  // `getPolyfills()` method and the `polyfillModuleNames` variable).
+  const polyfillModuleNames = options
+    .getPolyfills({
+      platform: bundleOptions.platform,
+    })
+    .concat(options.polyfillModuleNames);
+
+  const dependencyGraph = await bundler.getDependencyGraph();
+
+  // Build the module system dependencies (scripts that need to
+  // be included at the very beginning of the bundle) + any polifyll.
+  const modules = [defaults.moduleSystem]
+    .concat(polyfillModuleNames)
+    .map(polyfillModuleName =>
+      dependencyGraph.createPolyfill({
+        file: polyfillModuleName,
+      }),
+    );
+
+  const transformOptions = {
+    dev: bundleOptions.dev,
+    enableBabelRCLookup: options.enableBabelRCLookup,
+    hot: bundleOptions.hot,
+    projectRoot: options.projectRoots[0],
+  };
+
+  const out = await Promise.all(
+    modules.map(module => _createEdgeFromScript(module, transformOptions)),
+  );
+
+  out.unshift(_getPrelude({dev: bundleOptions.dev}));
+
+  return out;
+}
+
+function _getPrelude({dev}: {dev: boolean}): DependencyEdge {
+  const code = getPreludeCode({isDev: dev});
+  const name = '__prelude__';
+
+  return {
+    dependencies: new Map(),
+    inverseDependencies: new Set(),
+    path: name,
+    output: {
+      code,
+      map: [],
+      source: code,
+      type: 'script',
+    },
+  };
+}
+
+async function _createEdgeFromScript(
+  module: Module,
+  options: {
+    dev: boolean,
+    enableBabelRCLookup: boolean,
+    hot: boolean,
+    projectRoot: string,
+  },
+): Promise<DependencyEdge> {
+  const result = await module.read({
+    assetDataPlugins: [],
+    customTransformOptions: {},
+    dev: options.dev,
+    enableBabelRCLookup: options.enableBabelRCLookup,
+    hot: options.hot,
+    inlineRequires: false,
+    minify: false,
+    platform: undefined,
+    projectRoot: options.projectRoot,
+  });
+
+  return {
+    dependencies: new Map(),
+    inverseDependencies: new Set(),
+    path: module.path,
+    output: {
+      code: result.code,
+      map: result.map,
+      source: result.source,
+      type: 'script',
+    },
+  };
+}
+
+module.exports = getPrependedScripts;

packages/metro/src/lib/mapGraph.js

@@ -0,0 +1,40 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ * @format
+ */
+
+'use strict';
+
+import type {DependencyEdge} from '../DeltaBundler/traverseDependencies';
+import type {Graph} from '../DeltaBundler';
+
+/**
+ * Generates a new Graph object, which has all the dependencies returned by the
+ * mapping function (similar to Array.prototype.map).
+ **/
+async function mapGraph(
+  graph: Graph,
+  mappingFn: DependencyEdge => Promise<DependencyEdge>,
+): Promise<Graph> {
+  const dependencies = new Map(
+    await Promise.all(
+      Array.from(graph.dependencies.entries()).map(async ([path, module]) => {
+        const mutated = await mappingFn(module);
+
+        return [path, mutated];
+      }),
+    ),
+  );
+
+  return {
+    dependencies,
+    entryPoints: graph.entryPoints,
+  };
+}
+
+module.exports = mapGraph;