feat: check modern build file in modern mode (#4467)

[skip release]

packages/vue-renderer/src/renderer.js

@@ -103,10 +103,16 @@ export default class VueRenderer {
       await this.loadResources(fs)
 
       // Verify
-      if (!this.isReady && this.context.options._start) {
+      if (this.context.options._start) {
+        if (!this.isReady) {
           throw new Error(
             'No build files found. Use either `nuxt build` or `builder.build()` or start nuxt in development mode.'
           )
+        } else if (this.context.options.modern && !this.context.resources.modernManifest) {
+          throw new Error(
+            'No modern build files found. Use either `nuxt build --modern` or `modern` option to build modern files.'
+          )
+        }
       }
     } else {
       // Development: Listen on build:resources hook

test/unit/renderer.test.js

@@ -1,9 +1,15 @@
+import path from 'path'
 import consola from 'consola'
 import { Nuxt } from '../utils'
 
 const NO_BUILD_MSG = 'No build files found. Use either `nuxt build` or `builder.build()` or start nuxt in development mode.'
+const NO_MODERN_BUILD_MSG = 'No modern build files found. Use either `nuxt build --modern` or `modern` option to build modern files.'
 
 describe('renderer', () => {
+  afterEach(() => {
+    consola.fatal.mockClear()
+  })
+
   test('detect no-build (Universal)', async () => {
     const nuxt = new Nuxt({
       _start: true,
@@ -27,4 +33,16 @@ describe('renderer', () => {
     await expect(nuxt.renderer.renderer.isReady).toBe(false)
     expect(consola.fatal).toHaveBeenCalledWith(new Error(NO_BUILD_MSG))
   })
+  test('detect no-modern-build', async () => {
+    const nuxt = new Nuxt({
+      _start: true,
+      mode: 'universal',
+      modern: 'client',
+      dev: false,
+      buildDir: path.resolve(__dirname, '..', 'fixtures', 'empty', '.nuxt')
+    })
+    await nuxt.ready()
+    await expect(nuxt.renderer.renderer.isReady).toBe(true)
+    expect(consola.fatal).toHaveBeenCalledWith(new Error(NO_MODERN_BUILD_MSG))
+  })
 })