Clean up babelModeV7 migration and code

MIGRATION.md

@@ -15,12 +15,11 @@
     - [start-storybook / build-storybook binaries removed](#start-storybook--build-storybook-binaries-removed)
     - [storyStoreV7 enabled by default](#storystorev7-enabled-by-default)
     - [Webpack4 support discontinued](#webpack4-support-discontinued)
-    - [Modern ESM / IE11 support discontinued](#modern-esm--ie11-support-discontinued)
     - [Framework field mandatory](#framework-field-mandatory)
     - [frameworkOptions renamed](#frameworkoptions-renamed)
     - [Framework standalone build moved](#framework-standalone-build-moved)
     - [Docs modern inline rendering by default](#docs-modern-inline-rendering-by-default)
-    - [Babel mode v7 by default](#babel-mode-v7-by-default)
+    - [Babel mode v7 exclusively](#babel-mode-v7-exclusively)
     - [7.0 feature flags removed](#70-feature-flags-removed)
     - [CLI option `--use-npm` deprecated](#cli-option---use-npm-deprecated)
     - [Vite builder uses vite config automatically](#vite-builder-uses-vite-config-automatically)
@@ -474,10 +473,6 @@ To upgrade:
 
 During the 7.0 dev cycle we will be updating this section with useful resources as we run across them.
 
-#### Modern ESM / IE11 support discontinued
-
-SB7.0 compiles to modern ESM, meaning that IE11 is no longer supported. Over the course of the 7.0 dev cycle we will create recommendations for users who still require IE support.
-
 #### Framework field mandatory
 
 In 6.4 we introduced a new `main.js` field called [`framework`](#mainjs-framework-field). Starting in 7.0, this field is mandatory.
@@ -550,18 +545,18 @@ module.exports = {
 };
 ```
 
-#### Babel mode v7 by default
+#### Babel mode v7 exclusively
 
-Storybook now uses your project babel configuration differently as [described below in Babel Mode v7](#babel-mode-v7). This is now the default. To opt-out:
+Storybook now uses [Babel mode v7](#babel-mode-v7) exclusively. In 6.x, Storybook provided its own babel settings out of the box. Now, Storybook's uses your project's babel settings (`.babelrc`, `babel.config.js`, etc.) instead.
 
-```js
-module.exports = {
-  features: {
-    babelModeV7: false,
-  },
-};
+In the new mode, Storybook expects you to provide a configuration file. If you want a configuration file that's equivalent to the 6.x default, you can run the following command in your project directory:
+
+```sh
+npx sb@next babelrc
 ```
 
+This will create a `.babelrc.json` file. This file includes a bunch of babel plugins, so you may need to add new package devDependencies accordingly.
+
 #### 7.0 feature flags removed
 
 Storybook uses temporary feature flags to opt-in to future breaking changes or opt-in to legacy behaviors. For example:

code/lib/core-server/src/dev-server.ts

@@ -178,7 +178,6 @@ async function getStoryIndexGenerator(
     storyStoreV7?: boolean;
     breakingChangesV7?: boolean;
     interactionsDebugger?: boolean;
-    babelModeV7?: boolean;
     argTypeTargetsV7?: boolean;
     warnOnLegacyHierarchySeparator?: boolean;
   },

code/lib/core-server/src/presets/common-preset.ts

@@ -99,7 +99,6 @@ export const features = async (
   storyStoreV7: true,
   breakingChangesV7: true,
   interactionsDebugger: false,
-  babelModeV7: true,
   argTypeTargetsV7: true,
 });
 

code/lib/types/src/modules/core-common.ts

@@ -309,11 +309,6 @@ export interface StorybookConfig {
      */
     interactionsDebugger?: boolean;
 
-    /**
-     * Use Storybook 7.0 babel config scheme
-     */
-    babelModeV7?: boolean;
-
     /**
      * Filter args with a "target" on the type from the render function (EXPERIMENTAL)
      */

test-storybooks/external-docs/.storybook/main.cjs

@@ -22,7 +22,6 @@ const config = {
   features: {
     storyStoreV7: !global.navigator?.userAgent?.match?.('jsdom'),
     buildStoriesJson: true,
-    babelModeV7: true,
     warnOnLegacyHierarchySeparator: false,
     previewMdx2: true,
   },