fix: Ensure ergonomic handling of non-page in ./pages/

packages/next/build/index.ts

@@ -240,6 +240,19 @@ export default async function build(dir: string, conf = null): Promise<void> {
     const error = result.errors.join('\n\n')
 
     console.error(chalk.red('Failed to compile.\n'))
+
+    if (
+      error.indexOf('private-next-pages') > -1 &&
+      error.indexOf('does not contain a default export') > -1
+    ) {
+      const page_name_regex = /\'private-next-pages\/(?<page_name>[^\']*)\'/
+      const parsed = page_name_regex.exec(error)
+      const page_name = parsed && parsed.groups && parsed.groups.page_name
+      throw new Error(
+        `webpack build failed: found page without a React Component as default export in pages/${page_name}\n\nSee https://err.sh/zeit/next.js/page-without-valid-component for more info.`
+      )
+    }
+
     console.error(error)
     console.error()
 
@@ -371,9 +384,9 @@ export default async function build(dir: string, conf = null): Promise<void> {
 
   if (invalidPages.size > 0) {
     throw new Error(
-      `autoExport failed: found page${
+      `automatic static optimization failed: found page${
         invalidPages.size === 1 ? '' : 's'
-      } without React Component as default export\n${[...invalidPages]
+      } without a React Component as default export in \n${[...invalidPages]
         .map(pg => `pages${pg}`)
         .join(
           '\n'

test/integration/handle-non-page-in-pages/next.config.js

@@ -0,0 +1 @@
+module.exports = { target: 'serverless' }

test/integration/handle-non-page-in-pages/pages/invalid.tsx

@@ -0,0 +1,2 @@
+const Invalid = (): JSX.Element => <p>Hello world</p>
+export { Invalid }

test/integration/handle-non-page-in-pages/pages/valid.tsx

@@ -0,0 +1 @@
+export default (): JSX.Element => <p>Hello world</p>

test/integration/handle-non-page-in-pages/test/index.test.js

@@ -0,0 +1,18 @@
+/* eslint-env jest */
+/* global jasmine, test */
+import path from 'path'
+import { nextBuild } from 'next-test-utils'
+
+jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 2
+const appDir = path.join(__dirname, '..')
+
+describe('Handle non-page in pages when target: serverless', () => {
+  it('Fails softly with descriptive error', async () => {
+    const { stderr } = await nextBuild(appDir, [], { stderr: true })
+
+    expect(stderr).toMatch(
+      /webpack build failed: found page without a React Component as default export in/
+    )
+    expect(stderr).toMatch(/pages\/invalid/)
+  })
+})

test/integration/handle-non-page-in-pages/tsconfig.json

@@ -0,0 +1,29 @@
+{
+  "compilerOptions": {
+    "target": "es5",
+    "lib": [
+      "dom",
+      "dom.iterable",
+      "esnext"
+    ],
+    "allowJs": true,
+    "skipLibCheck": true,
+    "strict": false,
+    "forceConsistentCasingInFileNames": true,
+    "noEmit": true,
+    "esModuleInterop": true,
+    "module": "esnext",
+    "moduleResolution": "node",
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "jsx": "preserve"
+  },
+  "exclude": [
+    "node_modules"
+  ],
+  "include": [
+    "next-env.d.ts",
+    "**/*.ts",
+    "**/*.tsx"
+  ]
+}

test/integration/invalid-page-autoExport/test/index.test.js → test/integration/invalid-page-automatic-static-optimization/test/index.test.js

@@ -6,12 +6,12 @@ import { nextBuild } from 'next-test-utils'
 jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 2
 const appDir = path.join(__dirname, '..')
 
-describe('Invalid Page autoExport', () => {
+describe('Invalid Page automatic static optimization', () => {
   it('Fails softly with descriptive error', async () => {
     const { stderr } = await nextBuild(appDir, [], { stderr: true })
 
     expect(stderr).toMatch(
-      /autoExport failed: found pages without React Component as default export/
+      /automatic static optimization failed: found pages without a React Component as default export in/
     )
     expect(stderr).toMatch(/pages\/invalid/)
     expect(stderr).toMatch(/pages\/also-invalid/)