fix(nuxt): scan folder indices for middleware (#27187)

docs/1.getting-started/12.upgrade.md

@@ -252,6 +252,34 @@ However, if you are a module author using the `builder:watch` hook and wishing t
   })
 ```
 
+#### Directory index scanning
+
+🚦 **Impact Level**: Medium
+
+##### What Changed
+
+Child folders in your `middleware/` folder are also scanned for `index` files and these are now also registered as middleware in your project.
+
+##### Reasons for Change
+
+Nuxt scans a number of folders automatically, including `middleware/` and `plugins/`.
+
+Child folders in your `plugins/` folder are scanned for `index` files and we wanted to make this behavior consistent between scanned directories.
+
+##### Migration Steps
+
+Probably no migration is necessary but if you wish to revert to previous behavior you can add a hook to filter out these middleware:
+
+```ts
+export default defineNuxtConfig({
+  hooks: {
+    'app:resolve'(app) {
+      app.middleware = app.middleware.filter(mw => !/\/index\.[^/]+$/.test(mw.path))
+    }
+  }
+})
+```
+
 #### Template Compilation Changes
 
 🚦 **Impact Level**: Minimal

packages/kit/src/plugin.ts

@@ -3,7 +3,6 @@ import type { NuxtPlugin, NuxtPluginTemplate } from '@nuxt/schema'
 import { useNuxt } from './context'
 import { addTemplate } from './template'
 import { resolveAlias } from './resolve'
-import { logger } from './logger'
 
 /**
  * Normalize a nuxt plugin object
@@ -20,12 +19,6 @@ export function normalizePlugin (plugin: NuxtPlugin | string): NuxtPlugin {
     throw new Error('Invalid plugin. src option is required: ' + JSON.stringify(plugin))
   }
 
-  // TODO: only scan top-level files #18418
-  const nonTopLevelPlugin = plugin.src.match(/\/plugins\/[^/]+\/index\.[^/]+$/i)
-  if (nonTopLevelPlugin && nonTopLevelPlugin.length > 0 && !useNuxt().options.plugins.find(i => (typeof i === 'string' ? i : i.src).endsWith(nonTopLevelPlugin[0]))) {
-    logger.warn(`[deprecation] You are using a plugin that is within a subfolder of your plugins directory without adding it to your config explicitly. You can move it to the top-level plugins directory, or include the file '~${nonTopLevelPlugin[0]}' in your plugins config (https://nuxt.com/docs/api/nuxt-config#plugins-1) to remove this warning.`)
-  }
-
   // Normalize full path to plugin
   plugin.src = normalize(resolveAlias(plugin.src))
 

packages/nuxt/src/core/app.ts

@@ -179,7 +179,12 @@ export async function resolveApp (nuxt: Nuxt, app: NuxtApp) {
   app.middleware = []
   for (const config of reversedConfigs) {
     const middlewareDir = (config.rootDir === nuxt.options.rootDir ? nuxt.options : config).dir?.middleware || 'middleware'
-    const middlewareFiles = await resolveFiles(config.srcDir, `${middlewareDir}/*{${nuxt.options.extensions.join(',')}}`)
+    const middlewareFiles = await resolveFiles(config.srcDir, [
+      `${middlewareDir}/*{${nuxt.options.extensions.join(',')}}`,
+      ...nuxt.options.future.compatibilityVersion === 4
+        ? [`${middlewareDir}/*/index{${nuxt.options.extensions.join(',')}}`]
+        : [],
+    ])
     for (const file of middlewareFiles) {
       const name = getNameFromPath(file)
       if (!name) {
@@ -200,7 +205,7 @@ export async function resolveApp (nuxt: Nuxt, app: NuxtApp) {
       ...config.srcDir
         ? await resolveFiles(config.srcDir, [
           `${pluginDir}/*{${nuxt.options.extensions.join(',')}}`,
-          `${pluginDir}/*/index{${nuxt.options.extensions.join(',')}}`, // TODO: remove, only scan top-level plugins #18418
+          `${pluginDir}/*/index{${nuxt.options.extensions.join(',')}}`,
         ])
         : [],
     ].map(plugin => normalizePlugin(plugin as NuxtPlugin)))