Clear up production build missing message for `next start` and `next export` (#19777)

Adds an err.sh link to the production build missing message. Also clears up `valid` as `production`.

Also fixes an edge case where an unhelpful error would be thrown because we checked for `.next` instead of `.next/BUILD_ID`

Added the out directory location as the list line during export to make sure people know where the files are output. 

Fixes #19778
Fixes #19788

errors/next-export-no-build-id.md

+# Could not find a production build
+
+#### Why This Error Occurred
+
+When running `next export` a production build is needed.
+
+#### Possible Ways to Fix It
+
+- Run `next build` to create a production build before running `next export`.
+- If your intention was to run the development server run `next dev` instead.

errors/production-start-no-build-id.md

+# Could not find a production build
+
+#### Why This Error Occurred
+
+When running `next start` or a custom server in production mode a production build is needed.
+
+#### Possible Ways to Fix It
+
+- Run `next build` to create a production build before booting up the production server.
+- If your intention was to run the development server run `next dev` instead.

packages/next/cli/next-export.ts

@@ -62,7 +62,7 @@ const nextExport: cliCommand = (argv) => {
 
   exportApp(dir, options)
     .then(() => {
-      printAndExit('Export successful', 0)
+      printAndExit(`Export successful. Files written to ${options.outdir}`, 0)
     })
     .catch((err) => {
       printAndExit(err)

packages/next/export/index.ts

@@ -164,9 +164,11 @@ export default async function exportApp(
     Log.info(`using build directory: ${distDir}`)
   }
 
-  if (!existsSync(distDir)) {
+  const buildIdFile = join(distDir, BUILD_ID_FILE)
+
+  if (!existsSync(buildIdFile)) {
     throw new Error(
-      `Build directory ${distDir} does not exist. Make sure you run "next build" before running "next start" or "next export".`
+      `Could not find a production build in the '${distDir}' directory. Try building your app with 'next build' before starting the static export. https://err.sh/vercel/next.js/next-export-no-build-id`
     )
   }
 
@@ -186,7 +188,7 @@ export default async function exportApp(
     )
   }
 
-  const buildId = readFileSync(join(distDir, BUILD_ID_FILE), 'utf8')
+  const buildId = readFileSync(buildIdFile, 'utf8')
   const pagesManifest =
     !options.pages &&
     (require(join(

packages/next/next-server/server/next-server.ts

@@ -1899,7 +1899,7 @@ export default class Server {
     } catch (err) {
       if (!fs.existsSync(buildIdFile)) {
         throw new Error(
-          `Could not find a valid build in the '${this.distDir}' directory! Try building your app with 'next build' before starting the server.`
+          `Could not find a production build in the '${this.distDir}' directory. Try building your app with 'next build' before starting the production server. https://err.sh/vercel/next.js/production-start-no-build-id`
         )
       }
 

test/integration/export-no-build/next.config.js

+module.exports = {
+  onDemandEntries: {
+    // Make sure entries are not getting disposed.
+    maxInactiveAge: 1000 * 60 * 60,
+  },
+  rewrites() {
+    // add a rewrite so the code isn't dead-code eliminated
+    return [
+      {
+        source: '/some-rewrite',
+        destination: '/',
+      },
+    ]
+  },
+  redirects() {
+    return [
+      {
+        source: '/redirect/me/to-about/:lang',
+        destination: '/:lang/about',
+        permanent: false,
+      },
+      {
+        source: '/nonexistent',
+        destination: '/about',
+        permanent: false,
+      },
+      {
+        source: '/shadowed-page',
+        destination: '/about',
+        permanent: false,
+      },
+      {
+        source: '/redirect-query-test/:path',
+        destination: '/about?foo=:path',
+        permanent: false,
+      },
+    ]
+  },
+}

test/integration/export-no-build/test/index.test.js

+/* eslint-env jest */
+import { nextExport } from 'next-test-utils'
+import { join } from 'path'
+const appDir = join(__dirname, '../')
+jest.setTimeout(1000 * 60 * 5)
+
+describe('next export without build', () => {
+  it('should show error when there is no production build', async () => {
+    const result = await nextExport(appDir, {}, { stderr: true, stdout: true })
+    console.log(result.stdout, result.stderr)
+    expect(result.stderr).toMatch(/Could not find a production build in the/)
+  })
+})

test/integration/production-start-no-build/next.config.js

+module.exports = {
+  onDemandEntries: {
+    // Make sure entries are not getting disposed.
+    maxInactiveAge: 1000 * 60 * 60,
+  },
+  rewrites() {
+    // add a rewrite so the code isn't dead-code eliminated
+    return [
+      {
+        source: '/some-rewrite',
+        destination: '/',
+      },
+    ]
+  },
+  redirects() {
+    return [
+      {
+        source: '/redirect/me/to-about/:lang',
+        destination: '/:lang/about',
+        permanent: false,
+      },
+      {
+        source: '/nonexistent',
+        destination: '/about',
+        permanent: false,
+      },
+      {
+        source: '/shadowed-page',
+        destination: '/about',
+        permanent: false,
+      },
+      {
+        source: '/redirect-query-test/:path',
+        destination: '/about?foo=:path',
+        permanent: false,
+      },
+    ]
+  },
+}

test/integration/production-start-no-build/test/index.test.js

+/* eslint-env jest */
+import { nextServer } from 'next-test-utils'
+import { join } from 'path'
+const appDir = join(__dirname, '../')
+jest.setTimeout(1000 * 60 * 5)
+
+describe('Production Usage without production build', () => {
+  it('should show error when there is no production build', async () => {
+    expect(() => {
+      nextServer({
+        dir: appDir,
+        dev: false,
+        quiet: true,
+      })
+    }).toThrow(/Could not find a production build in the/)
+  })
+})