Add support for runtimeConfigs in serverless mode

packages/next/build/entries.ts

@@ -67,6 +67,10 @@ export function createEntrypoints(
   const client: WebpackEntrypoints = {}
   const server: WebpackEntrypoints = {}
 
+  const hasRuntimeConfig =
+    Object.keys(config.publicRuntimeConfig).length > 0 ||
+    Object.keys(config.serverRuntimeConfig).length > 0
+
   const defaultServerlessOptions = {
     absoluteAppPath: pages['/_app'],
     absoluteDocumentPath: pages['/_document'],
@@ -77,6 +81,12 @@ export function createEntrypoints(
     generateEtags: config.generateEtags,
     canonicalBase: config.canonicalBase,
     basePath: config.experimental.basePath,
+    runtimeConfig: hasRuntimeConfig
+      ? JSON.stringify({
+          publicRuntimeConfig: config.publicRuntimeConfig,
+          serverRuntimeConfig: config.serverRuntimeConfig,
+        })
+      : '',
   }
 
   Object.keys(pages).forEach(page => {

packages/next/build/webpack/loaders/next-serverless-loader.ts

@@ -22,6 +22,7 @@ export type ServerlessLoaderQuery = {
   generateEtags: string
   canonicalBase: string
   basePath: string
+  runtimeConfig: string
 }
 
 const nextServerlessLoader: loader.Loader = function() {
@@ -37,6 +38,7 @@ const nextServerlessLoader: loader.Loader = function() {
     absoluteErrorPath,
     generateEtags,
     basePath,
+    runtimeConfig,
   }: ServerlessLoaderQuery =
     typeof this.query === 'string' ? parse(this.query.substr(1)) : this.query
 
@@ -50,6 +52,19 @@ const nextServerlessLoader: loader.Loader = function() {
   const escapedBuildId = escapeRegexp(buildId)
   const pageIsDynamicRoute = isDynamicRoute(page)
 
+  const runtimeConfigImports = runtimeConfig
+    ? `
+      import { setConfig } from 'next/dist/next-server/lib/runtime-config'
+    `
+    : ''
+
+  const runtimeConfigSetter = runtimeConfig
+    ? `
+      const runtimeConfig = ${runtimeConfig}
+      setConfig(runtimeConfig)
+    `
+    : 'const runtimeConfig = {}'
+
   const dynamicRouteImports = pageIsDynamicRoute
     ? `
     import { getRouteMatcher } from 'next/dist/next-server/lib/router/utils/route-matcher';
@@ -123,9 +138,14 @@ const nextServerlessLoader: loader.Loader = function() {
       import initServer from 'next-plugin-loader?middleware=on-init-server!'
       import onError from 'next-plugin-loader?middleware=on-error-server!'
       ${rewriteImports}
+      ${runtimeConfigImports}
 
       ${dynamicRouteMatcher}
       ${handleRewrites}
+      ${
+        /* this needs to be called before importing the API method */
+        runtimeConfigSetter
+      }
 
       export default async (req, res) => {
         try {
@@ -177,9 +197,16 @@ const nextServerlessLoader: loader.Loader = function() {
     import Document from '${absoluteDocumentPath}';
     import Error from '${absoluteErrorPath}';
     import App from '${absoluteAppPath}';
-    import * as ComponentInfo from '${absolutePagePath}';
     ${dynamicRouteImports}
     ${rewriteImports}
+    ${runtimeConfigImports}
+
+    ${
+      /* this needs to be called before importing the component */
+      runtimeConfigSetter
+    }
+
+    const ComponentInfo = require('${absolutePagePath}')
 
     const Component = ComponentInfo.default
     export default Component
@@ -214,6 +241,7 @@ const nextServerlessLoader: loader.Loader = function() {
         canonicalBase: "${canonicalBase}",
         buildId: "${buildId}",
         assetPrefix: "${assetPrefix}",
+        runtimeConfig: runtimeConfig.publicRuntimeConfig || {},
         ..._renderOpts
       }
       let _nextData = false

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

@@ -254,20 +254,6 @@ export default function loadConfig(
           : canonicalBase) || ''
     }
 
-    if (
-      userConfig.target &&
-      userConfig.target !== 'server' &&
-      ((userConfig.publicRuntimeConfig &&
-        Object.keys(userConfig.publicRuntimeConfig).length !== 0) ||
-        (userConfig.serverRuntimeConfig &&
-          Object.keys(userConfig.serverRuntimeConfig).length !== 0))
-    ) {
-      // TODO: change error message tone to "Only compatible with [fat] server mode"
-      throw new Error(
-        'Cannot use publicRuntimeConfig or serverRuntimeConfig with target=serverless https://err.sh/zeit/next.js/serverless-publicRuntimeConfig'
-      )
-    }
-
     if (
       userConfig.experimental?.reactMode &&
       !reactModes.includes(userConfig.experimental.reactMode)

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

@@ -11,7 +11,7 @@ describe('Handle non-page in pages when target: serverless', () => {
     const { stderr } = await nextBuild(appDir, [], { stderr: true })
 
     expect(stderr).toMatch(
-      /webpack build failed: found page without a React Component as default export in/
+      /found page without a React Component as default export in/
     )
     expect(stderr).toMatch(/pages\/invalid/)
   })

test/integration/serverless-runtime-configs/pages/config.js

@@ -0,0 +1,5 @@
+import getConfig from 'next/config'
+
+const config = getConfig()
+
+export default () => <p id="config">{JSON.stringify(config)}</p>

test/integration/serverless-runtime-configs/test/index.test.js

@@ -2,7 +2,15 @@
 /* global jasmine */
 import fs from 'fs-extra'
 import { join } from 'path'
-import { nextBuild } from 'next-test-utils'
+import {
+  nextBuild,
+  findPort,
+  nextStart,
+  killApp,
+  renderViaHTTP,
+} from 'next-test-utils'
+import cheerio from 'cheerio'
+import webdriver from 'next-webdriver'
 
 const appDir = join(__dirname, '../')
 const nextConfigPath = join(appDir, 'next.config.js')
@@ -14,7 +22,7 @@ describe('Serverless runtime configs', () => {
   beforeAll(() => cleanUp())
   afterAll(() => cleanUp())
 
-  it('should error on usage of publicRuntimeConfig', async () => {
+  it('should not error on usage of publicRuntimeConfig', async () => {
     await fs.writeFile(
       nextConfigPath,
       `module.exports = {
@@ -25,13 +33,16 @@ describe('Serverless runtime configs', () => {
     }`
     )
 
-    const { stderr } = await nextBuild(appDir, undefined, { stderr: true })
-    expect(stderr).toMatch(
+    const { stderr, code } = await nextBuild(appDir, undefined, {
+      stderr: true,
+    })
+    expect(code).toBe(0)
+    expect(stderr).not.toMatch(
       /Cannot use publicRuntimeConfig or serverRuntimeConfig/
     )
   })
 
-  it('should error on usage of serverRuntimeConfig', async () => {
+  it('should not error on usage of serverRuntimeConfig', async () => {
     await fs.writeFile(
       nextConfigPath,
       `module.exports = {
@@ -42,9 +53,63 @@ describe('Serverless runtime configs', () => {
     }`
     )
 
-    const { stderr } = await nextBuild(appDir, undefined, { stderr: true })
-    expect(stderr).toMatch(
+    const { stderr, code } = await nextBuild(appDir, undefined, {
+      stderr: true,
+    })
+    expect(code).toBe(0)
+    expect(stderr).not.toMatch(
       /Cannot use publicRuntimeConfig or serverRuntimeConfig/
     )
   })
+
+  it('should support runtime configs in serverless mode', async () => {
+    await fs.writeFile(
+      nextConfigPath,
+      `module.exports = {
+        target: 'serverless',
+        serverRuntimeConfig: {
+          hello: 'world'
+        },
+        publicRuntimeConfig: {
+          another: 'thing'
+        }
+      }`
+    )
+
+    await nextBuild(appDir, [], { stderr: true, stdout: true })
+    const appPort = await findPort()
+    const app = await nextStart(appDir, appPort, {
+      onStdout: console.log,
+      onStderr: console.log,
+    })
+
+    const browser = await webdriver(appPort, '/config')
+
+    const clientHTML = await browser.eval(`document.documentElement.innerHTML`)
+    const ssrHTML = await renderViaHTTP(appPort, '/config')
+
+    await killApp(app)
+    await fs.remove(nextConfigPath)
+
+    const ssr$ = cheerio.load(ssrHTML)
+    const client$ = cheerio.load(clientHTML)
+
+    const ssrConfig = ssr$('#config').text()
+    const clientConfig = client$('#config').text()
+
+    expect(JSON.parse(ssrConfig)).toEqual({
+      publicRuntimeConfig: {
+        another: 'thing',
+      },
+      serverRuntimeConfig: {
+        hello: 'world',
+      },
+    })
+    expect(JSON.parse(clientConfig)).toEqual({
+      publicRuntimeConfig: {
+        another: 'thing',
+      },
+      serverRuntimeConfig: {},
+    })
+  })
 })