BREAKING: Add regenerator-runtime on demand, based on the files

Summary:
Adding a Babel plugin that will analyze the file looking for any potential candidate to use `regenerator-runtime`, and if so, will inject dynamically the module. The module is injected per file, so we avoid polluting the global environment. The plugin is also able to inject the `require` call beforehand, so that the inliner can pick them and inline them.

The Babel plugin is part of `react-native-babel-preset`, so as long as you are using this preset you are safe. If not, you should include the specific transformer into your list of plugins, as `react-native-babel-preset/transforms/transform-regenerator-runtime-insertion.js`.

Reviewed By: davidaurelio

Differential Revision: D5388655

fbshipit-source-id: dc403f3d5e2d807529eb8569a85c45fec36a6a3e

lerna.json

@@ -1,5 +1,5 @@
 {
-  "version": "0.9.0",
+  "version": "0.10.0",
   "lerna": "2.0.0-rc.5",
   "npmClient": "yarn",
   "packages": [

packages/metro-bundler/package.json

@@ -1,5 +1,5 @@
 {
-  "version": "0.9.0",
+  "version": "0.10.0",
   "name": "metro-bundler",
   "description": "🚇 The JavaScript bundler for React Native.",
   "main": "src/index.js",
@@ -19,7 +19,7 @@
     "babel-plugin-external-helpers": "^6.18.0",
     "babel-preset-es2015-node": "^6.1.1",
     "babel-preset-fbjs": "^2.1.4",
-    "babel-preset-react-native": "^2.0.0",
+    "babel-preset-react-native": "^2.1.0",
     "babel-register": "^6.24.1",
     "babylon": "^6.17.0",
     "chalk": "^1.1.1",

packages/metro-bundler/src/JSTransformer/worker/__tests__/constant-folding-test.js

@@ -10,26 +10,28 @@
  */
 'use strict';
 
-const babel = require('babel-core');
+/* eslint-disable max-len */
+
 const constantFolding = require('../constant-folding');
 
-function parse(code) {
-  return babel.transform(code, {code: false, babelrc: false, compact: true});
-}
+const {transform, transformFromAst} = require('babel-core');
 
 const babelOptions = {
   babelrc: false,
   compact: true,
-  retainLines: false,
 };
 
-function normalize({code}) {
-  return babel.transform(code, babelOptions).code;
+function toString(ast) {
+  return normalize(transformFromAst(ast, babelOptions).code);
+}
+
+function normalize(code) {
+  return transform(code, babelOptions).code;
 }
 
 describe('constant expressions', () => {
   it('can optimize conditional expressions with constant conditions', () => {
-    const code = `
+    const before = `
       a(
         'production'=="production",
         'production'!=='development',
@@ -39,56 +41,97 @@ describe('constant expressions', () => {
         'android'==='android' ? {a:1} : {a:0},
         'foo'==='bar' ? b : c,
         f() ? g() : h()
-      );`;
-    expect(normalize(constantFolding('arbitrary.js', parse(code)))).toEqual(
-      'a(true,true,2,true,{},{a:1},c,f()?g():h());',
       );
+    `;
+
+    const after = `
+      a(
+        true,
+        true,
+        2,
+        true,
+        {},
+        {a:1},
+        c,
+        f() ? g() : h()
+      );
+    `;
+
+    const {ast} = constantFolding('arbitrary.js', {code: before});
+    expect(toString(ast)).toEqual(normalize(after));
   });
 
   it('can optimize ternary expressions with constant conditions', () => {
-    const code = `var a = true ? 1 : 2;
+    const before = `
+      var a = true ? 1 : 2;
       var b = 'android' == 'android'
         ? ('production' != 'production' ? 'a' : 'A')
-         : 'i';`;
-    expect(normalize(constantFolding('arbitrary.js', parse(code)))).toEqual(
-      "var a=1;var b='A';",
-    );
+        : 'i';
+    `;
+
+    const after = `
+      var a = 1;
+      var b = 'A';
+    `;
+
+    const {ast} = constantFolding('arbitrary.js', {code: before});
+    expect(toString(ast)).toEqual(normalize(after));
   });
 
   it('can optimize logical operator expressions with constant conditions', () => {
-    const code = `
+    const before = `
       var a = true || 1;
       var b = 'android' == 'android' &&
-        'production' != 'production' || null || "A";`;
-    expect(normalize(constantFolding('arbitrary.js', parse(code)))).toEqual(
-      'var a=true;var b="A";',
-    );
+        'production' != 'production' || null || "A";
+    `;
+
+    const after = `
+      var a = true;
+      var b = "A";
+    `;
+
+    const {ast} = constantFolding('arbitrary.js', {code: before});
+    expect(toString(ast)).toEqual(normalize(after));
   });
 
   it('can optimize logical operators with partly constant operands', () => {
-    const code = `
+    const before = `
       var a = "truthy" || z();
       var b = "truthy" && z();
       var c = null && z();
       var d = null || z();
       var e = !1 && z();
     `;
-    expect(normalize(constantFolding('arbitrary.js', parse(code)))).toEqual(
-      'var a="truthy";var b=z();var c=null;var d=z();var e=false;',
-    );
+
+    const after = `
+      var a = "truthy";
+      var b = z();
+      var c = null;
+      var d = z();
+      var e = false;
+    `;
+
+    const {ast} = constantFolding('arbitrary.js', {code: before});
+    expect(toString(ast)).toEqual(normalize(after));
   });
 
   it('can remode an if statement with a falsy constant test', () => {
-    const code = `
+    const before = `
       if ('production' === 'development' || false) {
         var a = 1;
       }
     `;
-    expect(normalize(constantFolding('arbitrary.js', parse(code)))).toEqual('');
+
+    // Intentionally empty: all dead code.
+    const after = `
+    `;
+
+    const {ast} = constantFolding('arbitrary.js', {code: before});
+    expect(toString(ast)).toEqual(normalize(after));
   });
 
   it('can optimize if-else-branches with constant conditions', () => {
-    const code = `
+    const before = `
       if ('production' == 'development') {
         var a = 1;
         var b = a + 2;
@@ -99,13 +142,20 @@ describe('constant expressions', () => {
         var a = 'b';
       }
     `;
-    expect(normalize(constantFolding('arbitrary.js', parse(code)))).toEqual(
-      '{var a=3;var b=a+4;}',
-    );
+
+    const after = `
+      {
+        var a = 3;
+        var b = a + 4;
+      }
+    `;
+
+    const {ast} = constantFolding('arbitrary.js', {code: before});
+    expect(toString(ast)).toEqual(normalize(after));
   });
 
   it('can optimize nested if-else constructs', () => {
-    const code = `
+    const before = `
       if ('ios' === "android") {
         if (true) {
           require('a');
@@ -120,8 +170,16 @@ describe('constant expressions', () => {
         }
       }
     `;
-    expect(normalize(constantFolding('arbitrary.js', parse(code)))).toEqual(
-      "{{require('c');}}",
-    );
+
+    const after = `
+      {
+        {
+          require('c');
+        }
+      }
+    `;
+
+    const {ast} = constantFolding('arbitrary.js', {code: before});
+    expect(toString(ast)).toEqual(normalize(after));
   });
 });

packages/metro-bundler/src/JSTransformer/worker/__tests__/worker-test.js

@@ -275,7 +275,7 @@ describe('code transformation worker:', () => {
       const inlineResult = {map: {version: 3, sources: []}, ast: {}};
       inline.mockReturnValue(inlineResult);
       transformCode(transformer, filename, filename, 'code', options, () => {
-        expect(constantFolding).toBeCalledWith(filename, inlineResult);
+        expect(constantFolding).toBeCalledWith(filename, inlineResult, options);
         done();
       });
     });

packages/metro-bundler/src/JSTransformer/worker/constant-folding.js

@@ -13,8 +13,9 @@
 'use strict';
 
 const babel = require('babel-core');
+const invariant = require('fbjs/lib/invariant');
 
-import type {Ast, SourceMap as MappingsMap} from 'babel-core';
+import type {IntermediateTransformResult} from './types.flow';
 const t = babel.types;
 
 const Conditional = {
@@ -31,7 +32,7 @@ const Conditional = {
   },
 };
 
-const plugin = {
+const constantFoldingPlugin = {
   visitor: {
     BinaryExpression: {
       exit(path) {
@@ -71,25 +72,32 @@ const plugin = {
   },
 };
 
+const plugin = () => constantFoldingPlugin;
+
 function constantFolding(
   filename: string,
-  transformResult: {
-    ast: Ast,
-    code?: ?string,
-    map: ?MappingsMap,
-  },
-) {
-  return babel.transformFromAst(transformResult.ast, transformResult.code, {
+  transformResult: IntermediateTransformResult,
+  options: {+dev: boolean, +platform: ?string},
+): IntermediateTransformResult {
+  const code = transformResult.code;
+  const babelOptions = {
     filename,
-    plugins: [plugin],
+    plugins: [[plugin, options]],
     inputSourceMap: transformResult.map,
     sourceMaps: true,
     sourceFileName: filename,
+    code: true,
     babelrc: false,
     compact: true,
-    retainLines: true,
-  });
+  };
+
+  const result = transformResult.ast
+    ? babel.transformFromAst(transformResult.ast, code, babelOptions)
+    : (code && babel.transform(code, babelOptions)) || {};
+  const {ast} = result;
+  invariant(ast != null, 'Missing AST in babel transform results.');
+  return {ast, code: result.code, map: result.map};
 }
 
-constantFolding.plugin = plugin;
+constantFolding.plugin = constantFoldingPlugin;
 module.exports = constantFolding;

packages/metro-bundler/src/JSTransformer/worker/index.js

@@ -22,7 +22,8 @@ const minify = require('./minify');
 import type {LogEntry} from '../../Logger/Types';
 import type {MappingsMap} from '../../lib/SourceMap';
 import type {LocalPath} from '../../node-haste/lib/toLocalPath';
-import type {Ast, Plugins as BabelPlugins} from 'babel-core';
+import type {IntermediateTransformResult} from './types.flow';
+import type {Plugins as BabelPlugins} from 'babel-core';
 
 export type TransformedCode = {
   code: string,
@@ -38,7 +39,7 @@ export type Transformer<ExtraOptions: {} = {}> = {
     options: ExtraOptions & TransformOptions,
     plugins?: BabelPlugins,
     src: string,
-  |}) => {ast: ?Ast, code: string, map: ?MappingsMap},
+  |}) => IntermediateTransformResult,
   getCacheKey: () => string,
 };
 
@@ -83,6 +84,8 @@ type TransformCode = (
   Callback<Data>,
 ) => void;
 
+const transformers = [inline, constantFolding];
+
 const transformCode: TransformCode = asyncify(
   (
     transformer: Transformer<*>,
@@ -121,17 +124,29 @@ const transformCode: TransformCode = asyncify(
       'Missing transform results despite having no error.',
     );
 
-    var code, map;
+    let code;
+    let map;
+
     if (options.minify) {
-      ({code, map} = constantFolding(
-        filename,
-        inline(filename, transformed, options),
-      ));
-      invariant(code != null, 'Missing code from constant-folding transform.');
+      let result = transformed;
+      const length = transformers.length;
+
+      for (let i = 0; i < length; i++) {
+        result = transformers[i](filename, result, options);
+      }
+
+      ({code, map} = result);
     } else {
       ({code, map} = transformed);
     }
 
+    invariant(
+      code != null,
+      'The last transformer on the list (' +
+        transformers[transformers.length - 1].name +
+        ') has to output code',
+    );
+
     if (isJson) {
       code = code.replace(/^\w+\.exports=/, '');
     } else {

packages/metro-bundler/src/JSTransformer/worker/inline.js

@@ -15,7 +15,7 @@
 const babel = require('babel-core');
 const invariant = require('fbjs/lib/invariant');
 
-import type {Ast, SourceMap as MappingsMap} from 'babel-core';
+import type {IntermediateTransformResult} from './types.flow';
 const t = babel.types;
 
 const React = {name: 'React'};
@@ -115,6 +115,16 @@ function findProperty(objectExpression, key, fallback) {
   return property ? property.value : fallback();
 }
 
+function checkRequireArgs(args, dependencyId) {
+  const pattern = t.stringLiteral(dependencyId);
+  return (
+    t.isStringLiteral(args[0], pattern) ||
+    (t.isMemberExpression(args[0]) &&
+      t.isNumericLiteral(args[0].property) &&
+      t.isStringLiteral(args[1], pattern))
+  );
+}
+
 const inlinePlugin = {
   visitor: {
     Identifier(path, state) {
@@ -162,27 +172,11 @@ const inlinePlugin = {
 
 const plugin = () => inlinePlugin;
 
-function checkRequireArgs(args, dependencyId) {
-  const pattern = t.stringLiteral(dependencyId);
-  return (
-    t.isStringLiteral(args[0], pattern) ||
-    (t.isMemberExpression(args[0]) &&
-      t.isNumericLiteral(args[0].property) &&
-      t.isStringLiteral(args[1], pattern))
-  );
-}
-
-type AstResult = {
-  ast: Ast,
-  code: ?string,
-  map: ?MappingsMap,
-};
-
 function inline(
   filename: string,
-  transformResult: {ast?: ?Ast, code: string, map: ?MappingsMap},
+  transformResult: IntermediateTransformResult,
   options: {+dev: boolean, +platform: ?string},
-): AstResult {
+): IntermediateTransformResult {
   const code = transformResult.code;
   const babelOptions = {
     filename,
@@ -197,7 +191,7 @@ function inline(
 
   const result = transformResult.ast
     ? babel.transformFromAst(transformResult.ast, code, babelOptions)
-    : babel.transform(code, babelOptions);
+    : (code && babel.transform(code, babelOptions)) || {};
   const {ast} = result;
   invariant(ast != null, 'Missing AST in babel transform results.');
   return {ast, code: result.code, map: result.map};

packages/metro-bundler/src/JSTransformer/worker/types.flow.js

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) 2017-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
+ * @format
+ */
+
+'use strict';
+
+import type {Ast, SourceMap as MappingsMap} from 'babel-core';
+
+export type IntermediateTransformResult = {
+  ast: ?Ast,
+  code: ?string,
+  map: ?MappingsMap,
+};

packages/metro-bundler/yarn.lock

@@ -536,9 +536,9 @@ babel-preset-fbjs@^2.1.4:
     babel-plugin-transform-react-display-name "^6.8.0"
     babel-plugin-transform-react-jsx "^6.8.0"
 
-babel-preset-react-native@^2.0.0:
-  version "2.0.0"
-  resolved "https://registry.yarnpkg.com/babel-preset-react-native/-/babel-preset-react-native-2.0.0.tgz#c26c7066c7399df30926fa03c012ef87f2cce5b7"
+babel-preset-react-native@^2.1.0:
+  version "2.1.0"
+  resolved "https://registry.yarnpkg.com/babel-preset-react-native/-/babel-preset-react-native-2.1.0.tgz#9013ebd82da1c88102bf588810ff59e209ca2b8a"
   dependencies:
     babel-plugin-check-es2015-constants "^6.5.0"
     babel-plugin-react-transform "2.0.2"