it actually works!

__tests__/e2e/.vitepress/config.ts

@@ -84,10 +84,21 @@ const sidebar: DefaultTheme.Config['sidebar'] = {
 }
 
 export default defineConfig({
+  vite: {
+    plugins: [
+      {
+        name: 'example',
+        configResolved(config) {
+          console.dir(config, { depth: 10 })
+        }
+      }
+    ]
+  },
   extends: [
     {
       title: 'Example',
-      description: 'An example app using VitePress.'
+      description: 'An example app using VitePress.',
+      additionalThemeFiles: ['./my-additional-theme-file.ts']
     },
     {
       themeConfig: {

__tests__/e2e/.vitepress/my-additional-theme-file.ts

@@ -0,0 +1,7 @@
+import type { Theme } from 'vitepress'
+
+export default {
+  enhanceApp({ app }) {
+    console.log('enhanceApp from my-additional-theme-file.ts')
+  }
+} satisfies Theme

src/client/app/index.ts

@@ -1,5 +1,5 @@
 import RawTheme from '@theme/index'
-import SiteConfigThemes from '@theme/site-config-themes'
+import SiteConfigThemes from '@site-config-themes'
 import {
   createApp as createClientApp,
   createSSRApp,

src/client/shim.d.ts

@@ -23,7 +23,7 @@ declare module '@theme/index' {
   export default theme
 }
 
-declare module '@theme/site-config-themes' {
+declare module '@site-config-themes' {
   import type { Theme } from 'vitepress'
   const themes: Theme[]
   export default themes

src/node/alias.ts

@@ -1,8 +1,9 @@
 import { createRequire } from 'module'
 import { resolve, join } from 'path'
-import { fileURLToPath, pathToFileURL } from 'url'
+import { fileURLToPath } from 'url'
 import type { Alias, AliasOptions } from 'vite'
 import type { SiteConfig } from './config'
+import fs from 'fs-extra'
 
 const require = createRequire(import.meta.url)
 const PKG_ROOT = resolve(fileURLToPath(import.meta.url), '../..')
@@ -27,16 +28,17 @@ export function resolveAliases(
   const { root, themeDir } = siteConfig
   const siteConfigThemesJS = `\
 ${siteConfig.additionalThemeFiles
-  .map((f, i) => `import $${i} from ${JSON.stringify(pathToFileURL(f))}`)
+  .map((f, i) => `import $${i} from ${JSON.stringify(f)}`)
   .join('\n')}
 export default [${siteConfig.additionalThemeFiles
     .map((f, i) => `$${i}`)
     .join(', ')}]`
+  const tmpfile = join(siteConfig.cacheDir, 'site-config-themes.ts')
+  fs.writeFileSync(tmpfile, siteConfigThemesJS)
+
   const paths: Record<string, string> = {
     '@theme': themeDir,
-    '@theme/site-config-themes': `data:text/javascript,${encodeURIComponent(
-      siteConfigThemesJS
-    )}`,
+    '@site-config-themes': tmpfile,
     [SITE_DATA_ID]: SITE_DATA_REQUEST_PATH
   }
 

src/node/config.ts

@@ -1,15 +1,13 @@
 import _debug from 'debug'
 import fs from 'fs-extra'
 import path from 'path'
-import url from 'url'
 import c from 'picocolors'
 import {
   createLogger,
   loadConfigFromFile,
   mergeConfig as mergeViteConfig,
   normalizePath,
-  type ConfigEnv,
-  type ResolvedConfig
+  type ConfigEnv
 } from 'vite'
 import { DEFAULT_THEME_PATH } from './alias'
 import { resolvePages } from './plugins/dynamicRoutesPlugin'
@@ -277,8 +275,8 @@ function resolveSiteDataHead(userConfig?: UserConfig): HeadConfig[] {
       typeof userConfig?.appearance === 'string'
         ? userConfig?.appearance
         : typeof userConfig?.appearance === 'object'
-        ? userConfig.appearance.initialValue ?? 'auto'
-        : 'auto'
+          ? userConfig.appearance.initialValue ?? 'auto'
+          : 'auto'
 
     head.push([
       'script',