feat(nuxt): auto-register modules in ~/modules

docs/2.guide/2.directory-structure/1.modules.md

@@ -0,0 +1,48 @@
+---
+navigation.icon: IconDirectory
+title: 'modules'
+head.title: 'modules/'
+description: Use the modules/ directory to automatically register local modules within your application.
+---
+
+# Modules Directory
+
+Nuxt scans the `modules/` directory and loads them before starting. It is a good place to place any local modules you develop while building your application.
+
+The auto-registered files patterns are:
+- `modules/*/index.ts`
+- `modules/*.ts`
+
+You don't need to add those local modules to your [`nuxt.config.ts`](/docs/guide/directory-structure/nuxt.config) separately.
+
+::code-group
+```ts [modules/hello/index.ts]
+// `nuxt/kit` is a helper subpath import you can use when defining local modules
+// that means you do not need to add `@nuxt/kit` to your project's dependencies
+import { createResolver, defineNuxtModule, addServerHandler } from 'nuxt/kit'
+
+export default defineNuxtModule({
+  meta: {
+    name: 'hello'
+  },
+  setup () {
+    const { resolve } = createResolver(import.meta.url)
+
+    // Add an API route
+    addServerHandler({
+      route: '/api/hello',
+      handler: resolve('./runtime/api-route')
+    })
+  }
+})
+```
+```ts [modules/hello/runtime/api-route.ts]
+export default defineEventHandler(() => {
+  return { hello: 'world' }
+}
+```
+::
+
+When starting Nuxt, the `hello` module will be registered and the `/api/hello` route will be available.
+
+:ReadMore{link="/docs/guide/going-further/modules"}

packages/nuxt/src/core/nuxt.ts

@@ -1,7 +1,7 @@
-import { join, normalize, resolve } from 'pathe'
+import { join, normalize, relative, resolve } from 'pathe'
 import { createHooks, createDebugger } from 'hookable'
 import type { LoadNuxtOptions } from '@nuxt/kit'
-import { loadNuxtConfig, nuxtCtx, installModule, addComponent, addVitePlugin, addWebpackPlugin, tryResolveModule, addPlugin } from '@nuxt/kit'
+import { resolvePath, resolveAlias, resolveFiles, loadNuxtConfig, nuxtCtx, installModule, addComponent, addVitePlugin, addWebpackPlugin, tryResolveModule, addPlugin } from '@nuxt/kit'
 
 import escapeRE from 'escape-string-regexp'
 import fse from 'fs-extra'
@@ -122,10 +122,38 @@ async function initNuxt (nuxt: Nuxt) {
 
   // Init user modules
   await nuxt.callHook('modules:before')
-  const modulesToInstall = [
-    ...nuxt.options.modules,
-    ...nuxt.options._modules
-  ]
+  const modulesToInstall = []
+
+  const watchedPaths = new Set<string>()
+  const specifiedModules = new Set<string>()
+
+  for (const _mod of nuxt.options.modules) {
+    const mod = Array.isArray(_mod) ? _mod[0] : _mod
+    if (typeof mod !== 'string') { continue }
+    const modPath = await resolvePath(resolveAlias(mod))
+    specifiedModules.add(modPath)
+  }
+
+  // Automatically register user modules
+  for (const config of nuxt.options._layers.map(layer => layer.config).reverse()) {
+    const layerModules = await resolveFiles(config.srcDir, [
+      `${config.dir?.modules || 'modules'}/*{${nuxt.options.extensions.join(',')}}`,
+      `${config.dir?.modules || 'modules'}/*/index{${nuxt.options.extensions.join(',')}}`
+    ])
+    for (const mod of layerModules) {
+      watchedPaths.add(relative(config.srcDir, mod))
+      if (specifiedModules.has(mod)) { continue }
+      specifiedModules.add(mod)
+      modulesToInstall.push(mod)
+    }
+  }
+
+  // Register user and then ad-hoc modules
+  modulesToInstall.push(...nuxt.options.modules, ...nuxt.options._modules)
+
+  nuxt.hooks.hookOnce('builder:watch', (event, path) => {
+    if (watchedPaths.has(path)) { nuxt.callHook('restart', { hard: true }) }
+  })
 
   // Add <NuxtWelcome>
   addComponent({

packages/schema/src/config/common.ts

@@ -219,6 +219,11 @@ export default defineUntypedSchema({
      */
     middleware: 'middleware',
 
+    /**
+     * The modules directory, each file in which will be auto-registered as a Nuxt module.
+     */
+    modules: 'modules',
+
     /**
      * The directory which will be processed to auto-generate your application page routes.
      */

test/basic.test.ts

@@ -46,6 +46,13 @@ describe('route rules', () => {
   })
 })
 
+describe('modules', () => {
+  it('should auto-register modules in ~/modules', async () => {
+    const result = await $fetch('/auto-registered-module')
+    expect(result).toEqual('handler added by auto-registered module')
+  })
+})
+
 describe('pages', () => {
   it('render index', async () => {
     const html = await $fetch('/')

test/fixtures/basic/modules/auto-registered/index.ts

@@ -0,0 +1,15 @@
+import { createResolver, defineNuxtModule, addServerHandler } from 'nuxt/kit'
+
+export default defineNuxtModule({
+  meta: {
+    name: 'auto-registered-module'
+  },
+  setup () {
+    const resolver = createResolver(import.meta.url)
+
+    addServerHandler({
+      handler: resolver.resolve('./runtime/handler'),
+      route: '/auto-registered-module'
+    })
+  }
+})

test/fixtures/basic/modules/auto-registered/runtime/handler.ts

@@ -0,0 +1 @@
+export default defineEventHandler(() => 'handler added by auto-registered module')

test/fixtures/basic/modules/example.ts

@@ -1,5 +1,4 @@
-import { fileURLToPath } from 'node:url'
-import { defineNuxtModule, addPlugin, useNuxt } from '@nuxt/kit'
+import { defineNuxtModule, createResolver, addPlugin, useNuxt } from 'nuxt/kit'
 
 export default defineNuxtModule({
   defaults: {
@@ -11,11 +10,13 @@ export default defineNuxtModule({
     configKey: 'sampleModule'
   },
   setup () {
-    addPlugin(fileURLToPath(new URL('./runtime/plugin', import.meta.url)))
+    const resolver = createResolver(import.meta.url)
+
+    addPlugin(resolver.resolve('./runtime/plugin'))
     useNuxt().hook('app:resolve', (app) => {
       app.middleware.push({
         name: 'unctx-test',
-        path: fileURLToPath(new URL('./runtime/middleware', import.meta.url)),
+        path: resolver.resolve('./runtime/middleware'),
         global: true
       })
     })