New babel config

packages/compat/src/babel.ts

@@ -0,0 +1,71 @@
+import { locateEmbroiderWorkingDir } from '@embroider/core';
+import { existsSync, readJSONSync } from 'fs-extra';
+import { join } from 'path';
+
+export function loadLegacyPlugins() {
+  const path = join(locateEmbroiderWorkingDir(process.cwd()), '_babel_config_.json');
+  if (!existsSync(path)) {
+    throw new Error(`Could not load the Babel plugins required by classic addons from ${path}`);
+  }
+
+  const { plugins } = readJSONSync(path);
+  _warnIfNoLegacyPlugins(plugins);
+  return plugins ?? [];
+}
+
+export function loadPluginDebugMacros() {
+  return [
+    [
+      'babel-plugin-debug-macros',
+      {
+        flags: [
+          {
+            source: '@glimmer/env',
+            flags: {
+              DEBUG: true,
+              CI: false,
+            },
+          },
+        ],
+        debugTools: {
+          isDebug: true,
+          source: '@ember/debug',
+          assertPredicateIndex: 1,
+        },
+        externalizeHelpers: {
+          module: '@ember/debug',
+        },
+      },
+      '@ember/debug stripping',
+    ],
+    [
+      'babel-plugin-debug-macros',
+      {
+        externalizeHelpers: {
+          module: '@ember/application/deprecations',
+        },
+        debugTools: {
+          isDebug: true,
+          source: '@ember/application/deprecations',
+          assertPredicateIndex: 1,
+        },
+      },
+      '@ember/application/deprecations stripping',
+    ],
+  ];
+}
+
+function _warnIfNoLegacyPlugins(legacyPlugins: any) {
+  if (!legacyPlugins || !legacyPlugins.length) {
+    console.warn(`
+      Your Ember app doesn't use any classic addon that requires Babel plugins.
+      In your babel.config.cjs, you can safely remove the usage of loadLegacyPlugins.
+
+      Remove:
+      - const { loadLegacyPlugins } = require('@embroider/compat');
+      - ...loadLegacyPlugins(),
+
+      If you install a classic addon in your app afterward, make sure to add any Babel config it may require to babel.config.cjs.
+    `);
+  }
+}

packages/compat/src/compat-app-builder.ts

@@ -581,6 +581,9 @@ export class CompatAppBuilder {
       `module.exports = ${JSON.stringify(pconfig.config, null, 2)}`,
       'utf8'
     );
+    outputJSONSync(join(locateEmbroiderWorkingDir(this.compatApp.root), '_babel_config_.json'), pconfig.config, {
+      spaces: 2,
+    });
     writeFileSync(
       join(locateEmbroiderWorkingDir(this.compatApp.root), '_babel_filter_.js'),
       babelFilterTemplate({ skipBabel: this.options.skipBabel, appRoot: this.origAppPackage.root }),

packages/compat/src/compat-app.ts

@@ -225,21 +225,8 @@ export default class CompatApp {
 
   @Memoize()
   babelConfig(): TransformOptions {
-    // this finds all the built-in babel configuration that comes with ember-cli-babel
-    const babelAddon = (this.legacyEmberAppInstance.project as any).findAddonByName('ember-cli-babel');
-    const babelConfig = babelAddon.buildBabelOptions({
-      'ember-cli-babel': {
-        ...this.legacyEmberAppInstance.options['ember-cli-babel'],
-        includeExternalHelpers: true,
-        compileModules: false,
-        disableDebugTooling: false,
-        disablePresetEnv: false,
-        disableEmberModulesAPIPolyfill: false,
-      },
-    });
-
-    let plugins = babelConfig.plugins as any[];
-    let presets = babelConfig.presets;
+    let plugins: any[] = [];
+    let presets: any[] = [];
 
     // this finds any custom babel configuration that's on the app (either
     // because the app author explicitly added some, or because addons have
@@ -250,7 +237,19 @@ export default class CompatApp {
         plugins = appBabel.plugins.concat(plugins);
       }
       if (appBabel.presets) {
-        presets = appBabel.presets.concat(presets);
+        if (this.legacyEmberAppInstance.options.useCustomBabelPresets) {
+          throw new Error(`
+            The following Babel presets have been found on the app custom Babel configuration:
+
+            ${presets}
+
+            Either these presets have been added explicitly to the app (e.g. through ember-cli-babel options in ember-cli-build.js), either classic addons have pushed these presets into the app.
+            With Embroider, you have full control over the Babel config via babel.config.cjs, and babel.config.cjs should be the only source of truth regarding Babel configuration; so classic addons no longer have the ability to push Babel presets.
+
+            1. Add the presets you want to use to the babel.config.cjs.
+            2. Once babel.config.cjs has the presets you need, remove the present error by setting "useCustomBabelPresets" to false in the build options.
+          `);
+        }
       }
     }
 

packages/compat/src/index.ts

@@ -1,3 +1,4 @@
+export { loadLegacyPlugins, loadPluginDebugMacros } from './babel';
 export { default as App } from './compat-app';
 export { default as Addons } from './compat-addons';
 export { default as Options, recommendedOptions } from './options';

packages/compat/src/options.ts

@@ -113,6 +113,14 @@ export default interface Options extends CoreOptions {
   // switching to Embroider, but is no longer necessary once content-for
   // 'config-module' code has been properly moved to the app-side.
   useAddonConfigModule?: boolean;
+
+  // Allows you to cancel the error that custom Babel presets have been
+  // found. This error notifies developers switching to Embroider that
+  // presets pushed by classic addons will no longer work. It also brings
+  // awareness about how to migrate from Babel build options to Babel config,
+  // but is no longer necessary once presets have been properly defined in the
+  // Babel config.
+  useCustomBabelPresets?: boolean;
 }
 
 const defaults = Object.assign(coreWithDefaults(), {
@@ -127,6 +135,7 @@ const defaults = Object.assign(coreWithDefaults(), {
   availableContentForTypes: [],
   useAddonAppBoot: true,
   useAddonConfigModule: true,
+  useCustomBabelPresets: true,
 });
 
 export function optionsWithDefaults(options?: Options): Required<Options> {