Don't require package.json at runtime (#5321)

* Remove obsolete check in dev-server

* Don’t require package.json at runtime

Inline the Next.js version at publish time, so that there’s no runtime dependency for this

.babelrc

-{
-  "presets": [
-    "@babel/preset-env",
-    "@babel/preset-react",
-    "@babel/preset-flow"
-  ],
-  "plugins": [
-    "@babel/plugin-syntax-dynamic-import",
-    "@babel/plugin-proposal-object-rest-spread",
-    "@babel/plugin-proposal-class-properties",
-    ["@babel/plugin-transform-runtime", {
-      "corejs": 2
-    }]
-  ]
-}

.babelrc.js

+module.exports = {
+  'presets': [
+    '@babel/preset-env',
+    '@babel/preset-react',
+    '@babel/preset-flow'
+  ],
+  'plugins': [
+    '@babel/plugin-syntax-dynamic-import',
+    '@babel/plugin-proposal-object-rest-spread',
+    '@babel/plugin-proposal-class-properties',
+    ['@babel/plugin-transform-runtime', {
+      'corejs': 2
+    }],
+    ['babel-plugin-transform-define', {
+      'process.env.NEXT_VERSION': require('./package.json').version
+    }]
+  ]
+}

package.json

@@ -125,6 +125,7 @@
     "@zeit/next-typescript": "1.1.0",
     "babel-eslint": "9.0.0",
     "babel-jest": "23.4.2",
+    "babel-plugin-transform-define": "1.3.0",
     "benchmark": "2.1.4",
     "cheerio": "0.22.0",
     "chromedriver": "2.42.0",

server/index.js

@@ -17,9 +17,6 @@ import * as asset from '../lib/asset'
 import * as envConfig from '../lib/runtime-config'
 import { isResSent } from '../lib/utils'
 
-// We need to go up one more level since we are in the `dist` directory
-import pkg from '../../package'
-
 export default class Server {
   constructor ({ dir = '.', staticMarkup = false, quiet = false, conf = null } = {}) {
     this.dir = resolve(dir)
@@ -192,7 +189,7 @@ export default class Server {
     }
 
     if (this.nextConfig.poweredByHeader) {
-      res.setHeader('X-Powered-By', `Next.js ${pkg.version}`)
+      res.setHeader('X-Powered-By', 'Next.js ' + process.env.NEXT_VERSION)
     }
     return sendHTML(req, res, html, req.method, this.renderOpts)
   }