Polyfill `Object.assign` by Default (#9369)

* Polyfill `Object.assign` by Default

* fix formatting

packages/next/build/polyfills/object-assign.js

+var assign = Object.assign.bind(Object)
+module.exports = assign
+module.exports.default = module.exports

packages/next/build/polyfills/object.assign/auto.js

+// noop

packages/next/build/polyfills/object.assign/implementation.js

+module.exports = Object.assign

packages/next/build/polyfills/object.assign/index.js

+var assign = Object.assign.bind(Object)
+function g() {
+  return assign
+}
+Object.defineProperties(g(), {
+  implementation: { get: g },
+  shim: { value: g },
+  getPolyfill: { value: g },
+})
+module.exports = g()

packages/next/build/polyfills/object.assign/polyfill.js

+module.exports = function() {
+  return Object.assign
+}

packages/next/build/polyfills/object.assign/shim.js

+module.exports = function() {
+  return Object.assign
+}

packages/next/build/webpack-config.ts

@@ -60,11 +60,27 @@ function getOptimizedAliases(isServer: boolean): { [pkg: string]: string } {
   }
 
   const stubWindowFetch = path.join(__dirname, 'polyfills', 'fetch.js')
+  const stubObjectAssign = path.join(__dirname, 'polyfills', 'object-assign.js')
+
+  const shimAssign = path.join(__dirname, 'polyfills', 'object.assign')
   return {
+    // Polyfill: Window#fetch
     __next_polyfill__fetch: require.resolve('whatwg-fetch'),
     unfetch$: stubWindowFetch,
     'isomorphic-unfetch$': stubWindowFetch,
     'whatwg-fetch$': stubWindowFetch,
+
+    // Polyfill: Object.assign
+    __next_polyfill__object_assign: require.resolve('object-assign'),
+    'object-assign$': stubObjectAssign,
+    '@babel/runtime-corejs2/core-js/object/assign': stubObjectAssign,
+
+    // Stub Package: object.assign
+    'object.assign/auto': path.join(shimAssign, 'auto.js'),
+    'object.assign/implementation': path.join(shimAssign, 'implementation.js'),
+    'object.assign$': path.join(shimAssign, 'index.js'),
+    'object.assign/polyfill': path.join(shimAssign, 'polyfill.js'),
+    'object.assign/shim': path.join(shimAssign, 'shim.js'),
   }
 }
 

packages/next/client/polyfills.js

 import '__next_polyfill__fetch'
+Object.assign = require('__next_polyfill__object_assign')