await config (#6488)

* await config

* update config-promise-error test

* Actually update test

packages/next/build/index.ts

@@ -56,14 +56,14 @@ export default async function build(dir: string, conf = null): Promise<void> {
   const pages = createPagesMapping(pagePaths, config.pageExtensions)
   const entrypoints = createEntrypoints(pages, config.target, buildId, config)
   const configs = [
-    getBaseWebpackConfig(dir, {
+    await getBaseWebpackConfig(dir, {
       buildId,
       isServer: false,
       config,
       target: config.target,
       entrypoints: entrypoints.client,
     }),
-    getBaseWebpackConfig(dir, {
+    await getBaseWebpackConfig(dir, {
       buildId,
       isServer: true,
       config,

packages/next/build/webpack-config.ts

@@ -299,9 +299,7 @@ export default function getBaseWebpackConfig (dir: string, {dev = false, isServe
 
     // @ts-ignore: Property 'then' does not exist on type 'Configuration'
     if (typeof webpackConfig.then === 'function') {
-      throw new Error(
-        '> Promise returned in next config. https://err.sh/zeit/next.js/promise-in-next-config.md'
-      )
+      console.warn('> Promise returned in next config. https://err.sh/zeit/next.js/promise-in-next-config.md')
     }
   }
 

test/integration/config-promise-error/test/index.test.js

@@ -30,8 +30,9 @@ describe('Promise in next config', () => {
     expect(stderr).toMatch(/Error: > Promise returned in next config\. https:\/\/err\.sh\/zeit\/next\.js\/promise-in-next-config\.md/)
   })
 
-  it('should throw error when a promise is returned on webpack', async () => {
+  it('should warn when a promise is returned on webpack', async () => {
     configFile.write(`
+      setTimeout(() => process.exit(0), 2 * 1000)
       module.exports = (phase, { isServer }) => {
         return {
           webpack: async (config) => {
@@ -46,6 +47,6 @@ describe('Promise in next config', () => {
       { stderr: true }
     )
 
-    expect(stderr).toMatch(/Error: > Promise returned in next config\. https:\/\/err\.sh\/zeit\/next\.js\/promise-in-next-config\.md/)
+    expect(stderr).toMatch(/> Promise returned in next config\. https:\/\/err\.sh\/zeit\/next\.js\/promise-in-next-config\.md/)
   })
 })