[FEAT] Adds an option to emit external babel helpers

This PR adds the `includeExternalHelpers` config option which allows
users to explicitly opt into using externalized helpers for transpiled
code. In large apps this can help with app size, especially in apps
which are making heavy usage of new ES features like native classes and
decorators.

This option is a _global_ option, meaning it _must_ be configured in the
root application. The reason for this is because there must be one
canonical source of truth for which version of helpers are being used,
and whether or not helpers are being used at all. If one addon decides
to use helpers, the app must include them, and they must be the right
version.

The current setup will _only_ support babel 7 helpers. This can be
expanded upon in the future, but the complexity of doing so makes it
beyond the scope of the initial work here.

.eslintrc.js

@@ -26,6 +26,7 @@ module.exports = {
         'blueprints/*/index.js',
         'config/**/*.js',
         'tests/dummy/config/**/*.js',
+        'lib/**/*.js'
       ],
       excludedFiles: [
         'addon/**',

README.md

@@ -94,6 +94,7 @@ interface EmberCLIBabelConfig {
   */
   'ember-cli-babel'?: {
     includePolyfill?: boolean;
+    includeExternalHelpers?: boolean;
     compileModules?: boolean;
     disableDebugTooling?: boolean;
     disablePresetEnv?: boolean;
@@ -159,6 +160,29 @@ let app = new EmberApp(defaults, {
 });
 ```
 
+#### External Helpers
+
+Babel often includes helper functions to handle some of the more complex logic
+in codemods. These functions are inlined by default, so they are duplicated in
+every file that they are used in, which adds some extra weight to final builds.
+
+Enabling `includeExternalHelpers` will cause Babel to import these helpers from
+a shared module, reducing app size overall. This option is available _only_ to
+the root application, because it is a global configuration value. There must be
+one agreed upon Babel version to generate helpers, and if any addon opts into
+generating helpers then they must be included and synced with any other addons
+and the root app.
+
+```js
+// ember-cli-build.js
+
+let app = new EmberApp(defaults, {
+  'ember-cli-babel': {
+    includeExternalHelpers: true
+  }
+});
+```
+
 #### Enabling Source Maps
 
 Babel generated source maps will enable you to debug your original ES6 source

ember-cli-build.js

@@ -19,10 +19,11 @@ module.exports = function(defaults) {
   let app = new EmberAddon(defaults, {
     'ember-cli-babel': {
       includePolyfill: true,
+      includeExternalHelpers: true,
       // ember-cli-babels defaults, should be parallelizable. If they are not,
       // it should fail to build. This flag being enabled ensure that to be the
       // case.
-      throwUnlessParallelizable: true
+      throwUnlessParallelizable: true,
     }
   });
 

index.js

@@ -84,19 +84,71 @@ module.exports = {
     }
   },
 
+  _shouldIncludeHelpers() {
+    let hostOptions = this._getHostOptions();
+    let customOptions = hostOptions['ember-cli-babel'];
+
+    if (customOptions && 'includeExternalHelpers' in customOptions) {
+      return customOptions.includeExternalHelpers === true;
+    } else {
+      return false;
+    }
+  },
+
+  _getHelperVersion() {
+    if (!this._helperVersion) {
+      let checker = new VersionChecker(this.project);
+      this._helperVersion = checker.for('@babel/core', 'npm').version;
+    }
+
+    return this._helperVersion;
+  },
+
+  _getHelpersPlugin() {
+    return [
+      [
+        require.resolve('./lib/inject-babel-helpers'),
+        {
+          helperVersion: this._getHelperVersion(),
+        }
+      ]
+    ]
+  },
+
+  treeForAddon() {
+    // Helpers are a global config, so only the root application should bother
+    // generating and including the file.
+    if (!(this.parent === this.project && this._shouldIncludeHelpers())) return;
+
+    const babel = require('@babel/core');
+    const writeFile = require('broccoli-file-creator');
+
+    let helpers = babel.buildExternalHelpers(null, 'module');
+    let babelHelpersTree = writeFile('ember-cli-babel/-private/helpers.js', helpers);
+
+    return this.transpileTree(babelHelpersTree, {
+      'ember-cli-babel': {
+        // prevents the helpers from being double transpiled, and including themselves
+        disablePresetEnv: true
+      }
+    });
+  },
+
   treeForVendor() {
-    if (!this._shouldIncludePolyfill()) { return; }
+    if (!this._shouldIncludePolyfill()) return;
 
     const Funnel = require('broccoli-funnel');
     const UnwatchedDir = require('broccoli-source').UnwatchedDir;
 
     // Find babel-core's browser polyfill and use its directory as our vendor tree
     let polyfillDir = path.dirname(require.resolve('@babel/polyfill/dist/polyfill'));
 
-    return new Funnel(new UnwatchedDir(polyfillDir), {
+    let polyfillTree = new Funnel(new UnwatchedDir(polyfillDir), {
       destDir: 'babel-polyfill'
     });
-  },
+
+    return polyfillTree;
+},
 
   included: function(app) {
     this._super.included.apply(this, arguments);
@@ -123,6 +175,12 @@ module.exports = {
     return (this.parent && this.parent.options) || (this.app && this.app.options) || {};
   },
 
+  _getHostOptions() {
+    let host = this._findHost();
+
+    return (host && host.options) || {};
+  },
+
   _parentName() {
     let parentName;
 
@@ -158,6 +216,7 @@ module.exports = {
   _getBabelOptions(config) {
     let addonProvidedConfig = this._getAddonProvidedConfig(config);
     let shouldCompileModules = this._shouldCompileModules(config);
+    let shouldIncludeHelpers = this._shouldIncludeHelpers();
 
     let emberCLIBabelConfig = config['ember-cli-babel'];
     let shouldRunPresetEnv = true;
@@ -188,6 +247,7 @@ module.exports = {
     let userPostTransformPlugins = addonProvidedConfig.postTransformPlugins;
 
     options.plugins = [].concat(
+      shouldIncludeHelpers && this._getHelpersPlugin(),
       userPlugins,
       this._getDebugMacroPlugins(config),
       this._getEmberModulesAPIPolyfill(config),

lib/inject-babel-helpers.js

@@ -0,0 +1,23 @@
+let { addNamed } = require('@babel/helper-module-imports')
+
+module.exports = function injectBabelHelpers(options) {
+  const { helperVersion = "7.0.0-beta.0" } = options;
+
+  return {
+    pre(file) {
+      file.set('helperGenerator', name => {
+        // If the helper didn't exist yet at the version given, we bail
+        // out and let Babel either insert it directly, or throw an error
+        // so that plugins can handle that case properly.
+        if (
+          file.availableHelper &&
+          !file.availableHelper(name, helperVersion)
+        ) {
+          return;
+        }
+
+        return addNamed(file.path, name, 'ember-cli-babel/-private/helpers');
+      });
+    },
+  };
+}

lib/relative-module-paths.js

@@ -1,4 +1,3 @@
-/* eslint-env node */
 'use strict';
 
 const path = require('path');

node-tests/addon-test.js

@@ -13,7 +13,11 @@ const createBuilder = BroccoliTestHelper.createBuilder;
 const createTempDir = BroccoliTestHelper.createTempDir;
 const terminateWorkerPool = require('./utils/terminate-workers');
 
-let Addon = CoreObject.extend(AddonMixin);
+let Addon = CoreObject.extend(AddonMixin).extend({
+  _findHost() {
+    return this.__host;
+  }
+});
 
 describe('ember-cli-babel', function() {
 
@@ -23,6 +27,7 @@ describe('ember-cli-babel', function() {
     this.ui = new MockUI();
     let project = { root: __dirname, emberCLIVersion: () => '2.16.2' };
     this.addon = new Addon({
+      __host: { options: {} },
       project,
       parent: project,
       ui: this.ui,
@@ -456,6 +461,30 @@ describe('ember-cli-babel', function() {
     });
   });
 
+  describe('_shouldIncludeHelpers()', function() {
+    it('should return false without any includeExternalHelpers option set', function() {
+      expect(this.addon._shouldIncludeHelpers()).to.be.false;
+    });
+
+    it('should return false with ember-cli-babel.includeExternalHelpers = true in parent', function() {
+      this.addon.parent.options = { 'ember-cli-babel': { includeExternalHelpers: true } };
+
+      expect(this.addon._shouldIncludeHelpers()).to.be.false;
+    });
+
+    it('should return true with ember-cli-babel.includeExternalHelpers = true in host', function() {
+      this.addon.__host.options = { 'ember-cli-babel': { includeExternalHelpers: true } };
+
+      expect(this.addon._shouldIncludeHelpers()).to.be.true;
+    });
+
+    it('should return false with ember-cli-babel.includeExternalHelpers = false in host', function() {
+      this.addon.__host.options = { 'ember-cli-babel': { includeExternalHelpers: false } };
+
+      expect(this.addon._shouldIncludeHelpers()).to.be.false;
+    });
+  });
+
   describe('_shouldCompileModules()', function() {
     beforeEach(function() {
       this.addon.parent = {

package.json

@@ -39,6 +39,7 @@
   },
   "dependencies": {
     "@babel/core": "^7.0.0",
+    "@babel/plugin-external-helpers": "^7.0.0",
     "@babel/plugin-transform-modules-amd": "^7.0.0",
     "@babel/polyfill": "^7.0.0",
     "@babel/preset-env": "^7.0.0",
@@ -48,7 +49,9 @@
     "babel-plugin-module-resolver": "^3.1.1",
     "broccoli-babel-transpiler": "^7.1.0",
     "broccoli-debug": "^0.6.4",
+    "broccoli-file-creator": "^2.1.1",
     "broccoli-funnel": "^2.0.1",
+    "broccoli-merge-trees": "^3.0.1",
     "broccoli-source": "^1.1.0",
     "clone": "^2.1.2",
     "ember-cli-version-checker": "^2.1.2",

tests/unit/external-helpers-test.js

@@ -0,0 +1,14 @@
+import { module, test } from 'qunit';
+
+module('Unit | external helpers test', function() {
+  test('external helpers work ', function(assert) {
+    assert.expect(0);
+
+    // This test will transpile to use external helpers depending on targets. If
+    // those helpers are not present, it will break. If IE11 is removed from
+    // targets we should find another way to test this.
+    class Foo {}
+
+    new Foo();
+  });
+});

yarn.lock

@@ -193,6 +193,13 @@
   version "7.0.0"
   resolved "https://registry.yarnpkg.com/@babel/parser/-/parser-7.0.0.tgz#697655183394facffb063437ddf52c0277698775"
 
+"@babel/plugin-external-helpers@^7.0.0":
+  version "7.0.0"
+  resolved "https://registry.yarnpkg.com/@babel/plugin-external-helpers/-/plugin-external-helpers-7.0.0.tgz#61ee7ba5dba27d7cad72a13d46bec23c060b762e"
+  integrity sha512-tZKTMdhZvTy0KCEX5EGQQm1RHr7jUa36q/yax1baEA0yZapVYmu10yW7LTqijITgSq416gPVjrcexiA6y4pJlA==
+  dependencies:
+    "@babel/helper-plugin-utils" "^7.0.0"
+
 "@babel/plugin-proposal-async-generator-functions@^7.0.0":
   version "7.0.0"
   resolved "https://registry.yarnpkg.com/@babel/plugin-proposal-async-generator-functions/-/plugin-proposal-async-generator-functions-7.0.0.tgz#5d1eb6b44fd388b97f964350007ab9da090b1d70"
@@ -1579,6 +1586,14 @@ broccoli-file-creator@^1.1.1:
     broccoli-plugin "^1.1.0"
     mkdirp "^0.5.1"
 
+broccoli-file-creator@^2.1.1:
+  version "2.1.1"
+  resolved "https://registry.yarnpkg.com/broccoli-file-creator/-/broccoli-file-creator-2.1.1.tgz#7351dd2496c762cfce7736ce9b49e3fce0c7b7db"
+  integrity sha512-YpjOExWr92C5vhnK0kmD81kM7U09kdIRZk9w4ZDCDHuHXW+VE/x6AGEOQQW3loBQQ6Jk+k+TSm8dESy4uZsnjw==
+  dependencies:
+    broccoli-plugin "^1.1.0"
+    mkdirp "^0.5.1"
+
 broccoli-funnel-reducer@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/broccoli-funnel-reducer/-/broccoli-funnel-reducer-1.0.0.tgz#11365b2a785aec9b17972a36df87eef24c5cc0ea"
@@ -1666,6 +1681,14 @@ broccoli-merge-trees@^3.0.0:
     broccoli-plugin "^1.3.0"
     merge-trees "^2.0.0"
 
+broccoli-merge-trees@^3.0.1:
+  version "3.0.1"
+  resolved "https://registry.yarnpkg.com/broccoli-merge-trees/-/broccoli-merge-trees-3.0.1.tgz#545dfe9f695cec43372b3ee7e63c7203713ea554"
+  integrity sha512-EFPBLbCoyCLdjJx0lxn+acWXK/GAZesXokS4OsF7HuB+WdnV76HVJPdfwp9TaXaUkrtb7eU+ymh9tY9wOGQjMQ==
+  dependencies:
+    broccoli-plugin "^1.3.0"
+    merge-trees "^2.0.0"
+
 broccoli-middleware@^1.2.1:
   version "1.2.1"
   resolved "https://registry.yarnpkg.com/broccoli-middleware/-/broccoli-middleware-1.2.1.tgz#a21f255f8bfe5a21c2f0fbf2417addd9d24c9436"