fix(schema): don't use `app/` as `srcDir` if it doesn't exist (#28176)

packages/nuxt/test/app.test.ts

@@ -19,7 +19,7 @@ describe('resolveApp', () => {
       {
         "components": [],
         "configs": [],
-        "dir": "<rootDir>/app",
+        "dir": "<rootDir>",
         "errorComponent": "<repoRoot>/packages/nuxt/src/app/components/nuxt-error-page.vue",
         "extensions": [
           ".js",

packages/schema/src/config/common.ts

@@ -118,15 +118,17 @@ export default defineUntypedSchema({
       }
 
       const srcDir = resolve(rootDir, 'app')
+      if (!existsSync(srcDir)) {
+        return rootDir
+      }
+
       const srcDirFiles = new Set<string>()
-      if (existsSync(srcDir)) {
       const files = await readdir(srcDir).catch(() => [])
       for (const file of files) {
         if (file !== 'spa-loading-template.html' && !file.startsWith('router.options')) {
           srcDirFiles.add(file)
         }
       }
-      }
       if (srcDirFiles.size === 0) {
         for (const file of ['app.vue', 'App.vue']) {
           if (existsSync(resolve(rootDir, file))) {

packages/schema/test/folder-structure.spec.ts

@@ -1,10 +1,14 @@
-import { describe, expect, it } from 'vitest'
+import { describe, expect, it, vi } from 'vitest'
 import { applyDefaults } from 'untyped'
 
 import { normalize } from 'pathe'
 import { NuxtConfigSchema } from '../src'
 import type { NuxtOptions } from '../src'
 
+vi.mock('node:fs', () => ({
+  existsSync: (id: string) => id.endsWith('app'),
+}))
+
 describe('nuxt folder structure', () => {
   it('should resolve directories for v3 setup correctly', async () => {
     const result = await applyDefaults(NuxtConfigSchema, {})