fix(nuxt): normalise rollup opts in island transform w/o nuxt (#26589)

packages/nuxt/src/components/islandsTransform.ts

@@ -8,6 +8,7 @@ import MagicString from 'magic-string'
 import { ELEMENT_NODE, parse, walk } from 'ultrahtml'
 import { hash } from 'ohash'
 import { resolvePath } from '@nuxt/kit'
+import defu from 'defu'
 import { isVue } from '../core/utils'
 
 interface ServerOnlyComponentTransformPluginOptions {
@@ -146,7 +147,7 @@ export const islandsTransform = createUnplugin((options: ServerOnlyComponentTran
  * extract attributes from a node
  */
 function extractAttributes (attributes: Record<string, string>, names: string[]) {
-  const extracted:Record<string, string> = {}
+  const extracted: Record<string, string> = {}
   for (const name of names) {
     if (name in attributes) {
       extracted[name] = attributes[name]
@@ -182,15 +183,27 @@ export const componentsChunkPlugin = createUnplugin((options: ComponentChunkOpti
     vite: {
       async config (config) {
         const components = options.getComponents()
-        config.build = config.build || {}
-        config.build.rollupOptions = config.build.rollupOptions || {}
-        config.build.rollupOptions.output = config.build.rollupOptions.output || {}
-        config.build.rollupOptions.input = config.build.rollupOptions.input || {}
+
+        config.build = defu(config.build, {
+          rollupOptions: {
+            input: {},
+            output: {}
+          }
+        })
+
+        const rollupOptions = config.build.rollupOptions!
+
+        if (typeof rollupOptions.input === 'string') {
+          rollupOptions.input = { entry: rollupOptions.input }
+        } else if (typeof rollupOptions.input === 'object' && Array.isArray(rollupOptions.input)) {
+          rollupOptions.input = rollupOptions.input.reduce<{ [key: string]: string }>((acc, input) => { acc[input] = input; return acc }, {})
+        }
+
         // don't use 'strict', this would create another "facade" chunk for the entry file, causing the ssr styles to not detect everything
-        config.build.rollupOptions.preserveEntrySignatures = 'allow-extension'
+        rollupOptions.preserveEntrySignatures = 'allow-extension'
         for (const component of components) {
           if (component.mode === 'client' || component.mode === 'all') {
-            (config.build.rollupOptions.input as Record<string, string>)[component.pascalName] = await resolvePath(component.filePath)
+            rollupOptions.input![component.pascalName] = await resolvePath(component.filePath)
           }
         }
       },