Add process env NEXT_RUNTIME

errors/env-key-not-allowed.md

@@ -2,8 +2,8 @@
 
 #### Why This Error Occurred
 
-Next.js configures internal variables for replacement itself. These start with `__` or `NODE_`, for this reason they are not allowed as values for `env` in `next.config.js`
+Next.js configures internal variables for replacement itself. `NEXT_RUNTIME` along with variables starting with `__` or `NODE_` are currently internal, for this reason they are not allowed as values for `env` in `next.config.js`
 
 #### Possible Ways to Fix It
 
-Rename the specified key so that it does not start with `__` or `NODE_`.
+Rename the specified key so that it does not start with `__` or `NODE_`, or pick other another name for `NEXT_RUNTIME`.

packages/next/bin/next.ts

@@ -104,6 +104,7 @@ if (process.env.NODE_ENV) {
 }
 
 ;(process.env as any).NODE_ENV = process.env.NODE_ENV || defaultEnv
+;(process.env as any).NEXT_RUNTIME = 'nodejs'
 
 // x-ref: https://github.com/vercel/next.js/pull/34688#issuecomment-1047994505
 if (process.versions.pnp === '3') {

packages/next/build/webpack-config.ts

@@ -1354,11 +1354,7 @@ export default async function getBaseWebpackConfig(
           {}
         ),
         ...Object.keys(config.env).reduce((acc, key) => {
-          if (/^(?:NODE_.+)|^(?:__.+)$/i.test(key)) {
-            throw new Error(
-              `The key "${key}" under "env" in ${config.configFileName} is not allowed. https://nextjs.org/docs/messages/env-key-not-allowed`
-            )
-          }
+          errorIfEnvConflicted(config, key)
 
           return {
             ...acc,
@@ -1369,11 +1365,16 @@ export default async function getBaseWebpackConfig(
         'process.env.NODE_ENV': JSON.stringify(
           dev ? 'development' : 'production'
         ),
+        ...(isServer && {
+          'process.env.NEXT_RUNTIME': JSON.stringify(
+            isEdgeRuntime ? 'edge' : 'nodejs'
+          ),
+        }),
         'process.env.__NEXT_NEW_LINK_BEHAVIOR': JSON.stringify(
           config.experimental.newNextLinkBehavior
         ),
         'process.env.__NEXT_CROSS_ORIGIN': JSON.stringify(crossOrigin),
-        'process.browser': JSON.stringify(targetWeb),
+        'process.browser': JSON.stringify(!isServer),
         'process.env.__NEXT_TEST_MODE': JSON.stringify(
           process.env.__NEXT_TEST_MODE
         ),
@@ -2182,3 +2183,14 @@ export default async function getBaseWebpackConfig(
 
   return webpackConfig
 }
+
+function errorIfEnvConflicted(config: NextConfigComplete, key: string) {
+  const isPrivateKey = /^(?:NODE_.+)|^(?:__.+)$/i.test(key)
+  const hasNextRuntimeKey = key === 'NEXT_RUNTIME'
+
+  if (isPrivateKey || hasNextRuntimeKey) {
+    throw new Error(
+      `The key "${key}" under "env" in ${config.configFileName} is not allowed. https://nextjs.org/docs/messages/env-key-not-allowed`
+    )
+  }
+}

packages/next/lib/chalk.ts

@@ -1,9 +1,9 @@
 let chalk: typeof import('next/dist/compiled/chalk')
 
-if (!process.browser) {
-  chalk = require('next/dist/compiled/chalk')
-} else {
+if (process.env.NEXT_RUNTIME === 'edge') {
   chalk = require('./web/chalk').default
+} else {
+  chalk = require('next/dist/compiled/chalk')
 }
 
 export default chalk

packages/next/pages/_document.tsx

@@ -80,7 +80,7 @@ function getPreNextWorkerScripts(context: HtmlProps, props: OriginProps) {
   const { assetPrefix, scriptLoader, crossOrigin, nextScriptWorkers } = context
 
   // disable `nextScriptWorkers` in edge runtime
-  if (!nextScriptWorkers || process.browser) return null
+  if (!nextScriptWorkers || process.env.NEXT_RUNTIME === 'edge') return null
 
   try {
     let {

packages/next/server/base-server.ts

@@ -1155,7 +1155,7 @@ export default abstract class Server {
       (isServerComponent &&
         !hasServerProps &&
         !hasGetInitialProps &&
-        !process.browser)
+        process.env.NEXT_RUNTIME !== 'edge')
 
     // Toggle whether or not this is a Data request
     const isDataReq =
@@ -1240,7 +1240,7 @@ export default abstract class Server {
 
     if (hasServerProps || isSSG) {
       // For the edge runtime, we don't support preview mode in SSG.
-      if (!process.browser) {
+      if (process.env.NEXT_RUNTIME !== 'edge') {
         const { tryGetPreviewData } =
           require('./api-utils/node') as typeof import('./api-utils/node')
         previewData = tryGetPreviewData(req, res, this.renderOpts.previewProps)
@@ -1758,7 +1758,10 @@ export default abstract class Server {
       )
 
       if (!isWrappedError) {
-        if ((this.minimalMode && !process.browser) || this.renderOpts.dev) {
+        if (
+          (this.minimalMode && process.env.NEXT_RUNTIME !== 'edge') ||
+          this.renderOpts.dev
+        ) {
           if (isError(err)) err.page = page
           throw err
         }

packages/next/server/render.tsx

@@ -89,7 +89,7 @@ let postProcess: typeof import('../shared/lib/post-process').default
 
 const DOCTYPE = '<!DOCTYPE html>'
 
-if (!process.browser) {
+if (process.env.NEXT_RUNTIME !== 'edge') {
   require('./node-polyfill-web-streams')
   optimizeAmp = require('./optimize-amp').default
   getFontDefinitionFromManifest =
@@ -518,7 +518,9 @@ export async function renderToHTML(
     Uint8Array,
     Uint8Array
   > | null =
-    isServerComponent && !process.browser ? new TransformStream() : null
+    isServerComponent && process.env.NEXT_RUNTIME !== 'edge'
+      ? new TransformStream()
+      : null
 
   if (isServerComponent) {
     serverComponentsInlinedTransformStream = new TransformStream()
@@ -700,7 +702,11 @@ export async function renderToHTML(
   let isPreview
   let previewData: PreviewData
 
-  if ((isSSG || getServerSideProps) && !isFallback && !process.browser) {
+  if (
+    (isSSG || getServerSideProps) &&
+    !isFallback &&
+    process.env.NEXT_RUNTIME !== 'edge'
+  ) {
     // Reads of this are cached on the `req` object, so this should resolve
     // instantly. There's no need to pass this data down from a previous
     // invoke, where we'd have to consider server & serverless.
@@ -775,7 +781,7 @@ export async function renderToHTML(
   }
 
   // Disable AMP under the web environment
-  const inAmpMode = !process.browser && isInAmpMode(ampState)
+  const inAmpMode = process.env.NEXT_RUNTIME !== 'edge' && isInAmpMode(ampState)
 
   const reactLoadableModules: string[] = []
 
@@ -1313,7 +1319,7 @@ export async function renderToHTML(
       | typeof Document
       | undefined
 
-    if (process.browser && Document.getInitialProps) {
+    if (process.env.NEXT_RUNTIME === 'edge' && Document.getInitialProps) {
       // In the Edge runtime, `Document.getInitialProps` isn't supported.
       // We throw an error here if it's customized.
       if (!builtinDocument) {
@@ -1323,7 +1329,10 @@ export async function renderToHTML(
       }
     }
 
-    if ((isServerComponent || process.browser) && Document.getInitialProps) {
+    if (
+      (isServerComponent || process.env.NEXT_RUNTIME === 'edge') &&
+      Document.getInitialProps
+    ) {
       if (builtinDocument) {
         Document = builtinDocument
       } else {
@@ -1541,7 +1550,7 @@ export async function renderToHTML(
 
       const hasDocumentGetInitialProps = !(
         isServerComponent ||
-        process.browser ||
+        process.env.NEXT_RUNTIME === 'edge' ||
         !Document.getInitialProps
       )
 
@@ -1560,7 +1569,7 @@ export async function renderToHTML(
 
       const { docProps } = (documentInitialPropsRes as any) || {}
       const documentElement = () => {
-        if (isServerComponent || process.browser) {
+        if (isServerComponent || process.env.NEXT_RUNTIME === 'edge') {
           return (Document as any)()
         }
 
@@ -1751,7 +1760,8 @@ export async function renderToHTML(
                 return html
               }
             : null,
-          !process.browser && process.env.__NEXT_OPTIMIZE_FONTS
+          process.env.NEXT_RUNTIME !== 'edge' &&
+          process.env.__NEXT_OPTIMIZE_FONTS
             ? async (html: string) => {
                 return await postProcess(
                   html,
@@ -1762,7 +1772,7 @@ export async function renderToHTML(
                 )
               }
             : null,
-          !process.browser && renderOpts.optimizeCss
+          process.env.NEXT_RUNTIME !== 'edge' && renderOpts.optimizeCss
             ? async (html: string) => {
                 // eslint-disable-next-line import/no-extraneous-dependencies
                 const Critters = require('critters')

packages/next/server/web/sandbox/context.ts

@@ -265,7 +265,9 @@ function buildEnvironmentVariablesFrom(
   keys: string[]
 ): Record<string, string | undefined> {
   const pairs = keys.map((key) => [key, process.env[key]])
-  return Object.fromEntries(pairs)
+  const env = Object.fromEntries(pairs)
+  env.NEXT_RUNTIME = 'edge'
+  return env
 }
 
 async function loadWasm(

packages/next/shared/lib/isomorphic/path.ts

@@ -1,5 +1,6 @@
-const path = process.browser
-  ? require('next/dist/compiled/path-browserify')
-  : require('path')
+const path =
+  process.env.NEXT_RUNTIME === 'edge'
+    ? require('next/dist/compiled/path-browserify')
+    : require('path')
 
 export default path

test/integration/middleware/core/test/index.test.js

@@ -119,6 +119,7 @@ describe('Middleware base tests', () => {
       context.app = await launchApp(context.appDir, context.appPort, {
         env: {
           MIDDLEWARE_TEST: 'asdf',
+          NEXT_RUNTIME: 'edge',
         },
       })
     })
@@ -130,6 +131,7 @@ describe('Middleware base tests', () => {
         process: {
           env: {
             MIDDLEWARE_TEST: 'asdf',
+            NEXT_RUNTIME: 'edge',
           },
           // it's poflyfilled since there is the "process" module
           // as a devDepencies of the next package

test/integration/production-config/next.config.js

@@ -15,6 +15,11 @@ module.exports = {
           SOME__ENV__VAR: '123',
         }
       : {}),
+    ...(process.env.ENABLE_ENV_NEXT_PRESERVED
+      ? {
+          NEXT_RUNTIME: 'nodejs',
+        }
+      : {}),
   },
   onDemandEntries: {
     // Make sure entries are not getting disposed.

test/integration/production-config/test/index.test.js

@@ -56,6 +56,16 @@ describe('Production Config Usage', () => {
       expect(result.stderr).toMatch(/The key "NODE_ENV" under/)
     })
 
+    it('should fail with NEXT_RUNTIME in env key', async () => {
+      const result = await runNextCommand(['build', appDir], {
+        env: { ENABLE_ENV_NEXT_PRESERVED: true },
+        stdout: true,
+        stderr: true,
+      })
+
+      expect(result.stderr).toMatch(/The key "NEXT_RUNTIME" under/)
+    })
+
     it('should allow __ within env key', async () => {
       const result = await runNextCommand(['build', appDir], {
         env: { ENABLE_ENV_WITH_UNDERSCORES: true },

test/integration/react-streaming-and-server-components/app/pages/runtime.js

@@ -1,5 +1,5 @@
 export default function () {
-  return process.version
+  return process.env.NEXT_RUNTIME === 'nodejs'
     ? `Runtime: Node.js ${process.version}`
     : 'Runtime: Edge/Browser'
 }

test/production/middleware-environment-variables-in-node-server-reflect-the-usage-inference/index.test.ts

@@ -44,6 +44,7 @@ describe('middleware environment variables in node server reflect the usage infe
       rest: {
         CAN_BE_INFERRED: 'can-be-inferred',
         X_CUSTOM_HEADER: 'x-custom-header',
+        NEXT_RUNTIME: 'edge',
       },
     })
   })