support site config .extends being an array

__tests__/e2e/.vitepress/config.ts

@@ -84,10 +84,18 @@ const sidebar: DefaultTheme.Config['sidebar'] = {
 }
 
 export default defineConfig({
-  title: 'Example',
+  extends: [
-  description: 'An example app using VitePress.',
+    {
+      title: 'Example',
+      description: 'An example app using VitePress.'
+    },
+    {
+      themeConfig: {
+        sidebar
+      }
+    }
+  ],
   themeConfig: {
-    sidebar,
     search: {
       provider: 'local',
       options: {

src/node/config.ts

@@ -180,8 +180,13 @@ async function resolveConfigExtends(
 ): Promise<UserConfig> {
   const resolved = await (typeof config === 'function' ? config() : config)
   if (resolved.extends) {
-    const base = await resolveConfigExtends(resolved.extends)
+    const extendsRaw = [resolved.extends].flat()
-    return mergeConfig(base, resolved)
+    const manyBases = await Promise.all(
+      extendsRaw.map((config) => resolveConfigExtends(config))
+    )
+    // or reduceRight() depending on which side gets priority
+    const singleBase = manyBases.reduce((prev, curr) => mergeConfig(prev, curr))
+    return mergeConfig(singleBase, resolved)
   }
   return resolved
 }

src/node/siteConfig.ts

@@ -56,7 +56,7 @@ export interface TransformPageContext {
 
 export interface UserConfig<ThemeConfig = any>
   extends LocaleSpecificConfig<ThemeConfig> {
-  extends?: RawConfigExports<ThemeConfig>
+  extends?: RawConfigExports<ThemeConfig> | RawConfigExports<ThemeConfig>[]
 
   base?: string
   srcDir?: string