feat: copy .env file in standalone mode (#34143)

Ref: #33897

I took a naive approach and simply added `.env` to the files that need to be copied.

Do we want to include `.env.production` as well? Ref: https://nextjs.org/docs/basic-features/environment-variables#loading-environment-variables

(I haven't tested what happens if the file does not exist on copy.)

Other files like `.env.*local` or `.env.{test,development}` don't make sense to copy.

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`


Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>

packages/next/build/babel/loader/index.ts

@@ -45,7 +45,7 @@ const nextBabelLoaderOuter = function nextBabelLoaderOuter(
       nextBabelLoader.call(this, loaderSpan, inputSource, inputSourceMap)
     )
     .then(
-      ([transformedSource, outputSourceMap]) =>
+      ([transformedSource, outputSourceMap]: any) =>
         callback?.(null, transformedSource, outputSourceMap || inputSourceMap),
       (err) => {
         callback?.(err)

packages/next/build/index.ts

@@ -427,7 +427,7 @@ export default async function build(
       pages404: boolean
       basePath: string
       redirects: Array<ReturnType<typeof buildCustomRoute>>
-      rewrites:
+      rewrites?:
         | Array<ReturnType<typeof buildCustomRoute>>
         | {
             beforeFiles: Array<ReturnType<typeof buildCustomRoute>>
@@ -2036,6 +2036,12 @@ export default async function build(
       for (const file of [
         ...requiredServerFiles.files,
         path.join(config.distDir, SERVER_FILES_MANIFEST),
+        ...loadedEnvFiles.reduce<string[]>((acc, envFile) => {
+          if (['.env', '.env.production'].includes(envFile.path)) {
+            acc.push(envFile.path)
+          }
+          return acc
+        }, []),
       ]) {
         const filePath = path.join(dir, file)
         await promises.copyFile(

packages/next/build/webpack/plugins/build-manifest-plugin.ts

@@ -28,7 +28,7 @@ function generateClientManifest(
   compilation: any,
   assetMap: BuildManifest,
   rewrites: CustomRoutes['rewrites']
-): string {
+): string | undefined {
   const compilationSpan = spans.get(compilation) || spans.get(compiler)
   const genClientManifestSpan = compilationSpan?.traceChild(
     'NextJsBuildManifest-generateClientManifest'

packages/next/trace/trace.ts

@@ -85,7 +85,7 @@ export class Span {
     this.attrs[key] = String(value)
   }
 
-  traceFn(fn: any) {
+  traceFn<T>(fn: () => T): T {
     try {
       return fn()
     } finally {

test/production/required-server-files.test.ts

@@ -31,6 +31,13 @@ describe('should set-up next', () => {
         'data.txt': new FileRef(
           join(__dirname, 'required-server-files/data.txt')
         ),
+        '.env': new FileRef(join(__dirname, 'required-server-files/.env')),
+        '.env.local': new FileRef(
+          join(__dirname, 'required-server-files/.env.local')
+        ),
+        '.env.production': new FileRef(
+          join(__dirname, 'required-server-files/.env.production')
+        ),
       },
       nextConfig: {
         eslint: {
@@ -722,4 +729,14 @@ describe('should set-up next', () => {
     const $ = cheerio.load(html)
     expect($('#slug-page').text()).toBe('[slug] page')
   })
+
+  it('should copy and read .env file', async () => {
+    const res = await fetchViaHTTP(appPort, '/api/env')
+
+    const envVariables = await res.json()
+
+    expect(envVariables.env).not.toBeUndefined()
+    expect(envVariables.envProd).not.toBeUndefined()
+    expect(envVariables.envLocal).toBeUndefined()
+  })
 })

test/production/required-server-files/.env

@@ -0,0 +1 @@
+FOO=bar

test/production/required-server-files/.env.local

@@ -0,0 +1 @@
+LOCAL_SECRET=local-secret

test/production/required-server-files/.env.production

@@ -0,0 +1 @@
+PROD_SECRET=prod-secret

test/production/required-server-files/pages/api/env.js

@@ -0,0 +1,7 @@
+export default function handler(_, res) {
+  res.json({
+    env: process.env.FOO,
+    envLocal: process.env.LOCAL_SECRET,
+    envProd: process.env.PROD_SECRET,
+  })
+}