Add bundle building logic

Summary: Adds the necessary functionality to serialize a series of `Module`s to a bundle and a source map in the context of the new Buck/Packager integration

Reviewed By: cpojer

Differential Revision: D4265867

fbshipit-source-id: f2d3e4ffed64a3dca817101faad7bced9f16edc7

packager/react-packager/src/ModuleGraph/output/as-plain-bundle.js

@@ -0,0 +1,51 @@
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+'use strict';
+
+const {createIndexMap} = require('./source-map');
+const {addModuleIdsToModuleWrapper} = require('./util');
+
+import type {Module} from '../types.flow';
+import type {SourceMap} from './source-map';
+
+module.exports = (
+  modules: Iterable<Module>,
+  filename?: string,
+  idForPath: {path: string} => number,
+): {code: string, map: SourceMap} => {
+  let code = '';
+  let line = 0;
+  const sections = [];
+
+  for (const module of modules) {
+    const {file} = module;
+    const moduleCode = file.type === 'module'
+      ? addModuleIdsToModuleWrapper(module, idForPath)
+      : file.code;
+
+    code += moduleCode + '\n';
+    if (file.map) {
+      sections.push({
+        map: file.map,
+        offset: {column: 0, line}
+      });
+    }
+    line += countLines(moduleCode);
+  }
+
+  return {code, map: createIndexMap({file: filename, sections})};
+};
+
+const reLine = /^/gm;
+function countLines(string: string): number {
+  //$FlowFixMe This regular expression always matches
+  return string.match(reLine).length;
+}

packager/react-packager/src/ModuleGraph/output/util.js

@@ -58,3 +58,12 @@ exports.createIdForPathFn = (): ({path: string} => number) => {
     return id;
   };
 };
+
+exports.virtualModule = (code: string): Module => ({
+  dependencies: [],
+  file: {
+    code,
+    path: '',
+    type: 'script',
+  }
+});

packager/react-packager/src/ModuleGraph/types.flow.js

@@ -13,8 +13,8 @@
 import type {Console} from 'console';
 
 export type Callback<A = void, B = void>
-  = ((error: Error) => mixed)
-  & ((error: null | void, a: A, b: B) => mixed);
+  = (Error => mixed)
+  & ((null | void, A, B) => mixed);
 
 type ResolveOptions = {
   log?: Console,
@@ -59,7 +59,7 @@ export type GraphFn = (
   callback?: Callback<GraphResult>,
 ) => void;
 
-type GraphResult = {
+export type GraphResult = {
   entryModules: Array<Module>,
   modules: Array<Module>,
 };