rsnext/test/integration/config/next.config.js

const withCSS = require('@zeit/next-css')
const withSass = require('@zeit/next-sass')
const path = require('path')
module.exports = withCSS(
  withSass({
    onDemandEntries: {
      // Make sure entries are not getting disposed.
      maxInactiveAge: 1000 * 60 * 60,
    },
    poweredByHeader: false,
    cssModules: true,
    serverRuntimeConfig: {
      mySecret: 'secret',
    },
    publicRuntimeConfig: {
      staticFolder: '/static',
    },
    env: {
      customVar: 'hello',
    },
    webpack(config, { dev, buildId, webpack }) {
      if (dev) {
        if (config.bail !== false) {
          throw new Error('Wrong bail value for development!')
        }
      } else {
        if (config.bail !== true) {
          throw new Error('Wrong bail value for production!')
        }
      }
      // When next-css is `npm link`ed we have to solve loaders from the project root
      const nextLocation = path.join(
        require.resolve('next/package.json'),
        '../'
      )
      const nextCssNodeModulesLocation = path.join(
        require.resolve('@zeit/next-css'),
        '../../../node_modules'
      )

      if (nextCssNodeModulesLocation.indexOf(nextLocation) === -1) {
        config.resolveLoader.modules.push(nextCssNodeModulesLocation)
      }
      config.plugins.push(
        new webpack.DefinePlugin({
          'process.env.CONFIG_BUILD_ID': JSON.stringify(buildId),
        })
      )

      return config
    },
  })
)