SvelteKit: Document svelteOptions in README

MIGRATION.md

@@ -23,10 +23,10 @@
     - [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)
-    - [Vite cache moved to node\_modules/.cache/.vite-storybook](#vite-cache-moved-to-node_modulescachevite-storybook)
+    - [Vite cache moved to node_modules/.cache/.vite-storybook](#vite-cache-moved-to-node_modulescachevite-storybook)
     - [SvelteKit needs the `@storybook/sveltekit` framework](#sveltekit-needs-the-storybooksveltekit-framework)
     - [Removed docs.getContainer and getPage parameters](#removed-docsgetcontainer-and-getpage-parameters)
-    - [Removed STORYBOOK\_REACT\_CLASSES global](#removed-storybook_react_classes-global)
+    - [Removed STORYBOOK_REACT_CLASSES global](#removed-storybook_react_classes-global)
     - [Icons API changed](#icons-api-changed)
     - ['config' preset entry replaced with 'previewAnnotations'](#config-preset-entry-replaced-with-previewannotations)
     - [Dropped support for Angular 12 and below](#dropped-support-for-angular-12-and-below)
@@ -275,6 +275,7 @@ To upgrade manually, add any version of `react` and `react-dom` as devDependenci
 ```
 npm add react react-dom --dev
 ```
+
 #### Postcss removed
 
 Storybook 6.x installed postcss by default. In 7.0 built-in support has been removed. IF you need it, you can add it back using [`@storybook/addon-postcss`](https://github.com/storybookjs/addon-postcss).
@@ -586,7 +587,7 @@ When using a [Vite-based framework](#framework-field-mandatory), Storybook will
 Some settings will be overridden by storybook so that it can function properly, and the merged settings can be modified using `viteFinal` in `.storybook/main.js` (see the [Storybook Vite configuration docs](https://storybook.js.org/docs/react/builders/vite#configuration)).  
 If you were using `viteFinal` in 6.5 to simply merge in your project's standard vite config, you can now remove it.
 
-For Svelte projects this means that the `svelteOptions` property in the `main.js` config can be omitted in most cases, as it will be loaded automatically via the project's `vite.config.js`. An exception to this is when the project needs different Svelte options for Storybook than the Vite config provides for the application itself.
+For Svelte projects this means that the `svelteOptions` property in the `main.js` config should be omitted, as it will be loaded automatically via the project's `vite.config.js`. An exception to this is when the project needs different Svelte options for Storybook than the Vite config provides for the application itself.
 
 #### Vite cache moved to node_modules/.cache/.vite-storybook
 

code/frameworks/sveltekit/README.md

@@ -13,6 +13,8 @@ Check out our [Frameworks API](https://storybook.js.org/blog/framework-api/) ann
   - [In a project with Storybook](#in-a-project-with-storybook)
     - [Automatic migration](#automatic-migration)
     - [Manual migration](#manual-migration)
+- [Troubleshooting](#troubleshooting)
+  - [Error: `ERR! SyntaxError: Identifier '__esbuild_register_import_meta_url__' has already been declared` when starting Storybook](#error-err-syntaxerror-identifier-__esbuild_register_import_meta_url__-has-already-been-declared-when-starting-storybook)
 - [Acknowledgements](#acknowledgements)
 
 ## Supported features
@@ -66,6 +68,8 @@ npx storybook@next upgrade --prerelease
 
 When running the `upgrade` command above you should get a prompt asking you to migrate to `@storybook/sveltekit`, which should handle everything for you. In some cases it can't migrate for you, eg. if your existing Storybook setup is based on Webpack. In such cases, refer to the manual migration below.
 
+Storybook 7.0 automatically loads your Vite config, and by extension your Svelte config. If you have a `svelteOptions` property in `.storybook/main.cjs` you need to remove that. See [Troubleshooting](#error-about-__esbuild_register_import_meta_url__-when-starting-storybook) below. We're working on doing this automatically soon.
+
 #### Manual migration
 
 Install the framework:
@@ -84,7 +88,7 @@ module.exports = {
 };
 ```
 
-Storybook 7.0 automatically loads your Vite config, and by extension your Svelte config. If you have a `svelteOptions` property in `main.cjs` you should remove that, unless you explicitly want different options between your app and Storybook.
+Storybook 7.0 automatically loads your Vite config, and by extension your Svelte config. If you have a `svelteOptions` property in `.storybook/main.cjs` you need to remove that. See [Troubleshooting](#error-about-__esbuild_register_import_meta_url__-when-starting-storybook) below.
 
 Remove any redundant dependencies, if you have them:
 
@@ -95,6 +99,18 @@ yarn remove storybook-builder-vite
 yarn remove @storybook/builder-vite
 ```
 
+## Troubleshooting
+
+### Error: `ERR! SyntaxError: Identifier '__esbuild_register_import_meta_url__' has already been declared` when starting Storybook
+
+> When starting Storybook after upgrading to v7.0, it breaks with the following error:
+>
+> ```
+> ERR! SyntaxError: Identifier '__esbuild_register_import_meta_url__' has already been declared
+> ```
+
+You'll get this error when upgrading from 6.5 to 7.0. You need to remove the `svelteOptions` property in `.storybook/main.cjs`, as that is not supported by Storybook 7.0 + SvelteKit. The property is also not necessary anymore because the Vite and Svelte configurations are loaded automatically in Storybook 7.0.
+
 ## Acknowledgements
 
 Integrating with SvelteKit would not have been possible if it weren't for the fantastic efforts by the Svelte core team - especially [Ben McCann](https://twitter.com/benjaminmccann) - to make integrations with the wider ecosystem possible.