From 6988a2e0a567bc78bd339ae4efbbb35a4311621f Mon Sep 17 00:00:00 2001
From: Tim Neutkens <tim@timneutkens.nl>
Date: Wed, 22 Jan 2020 16:24:02 +0100
Subject: [PATCH] Use builtins for React transform (#10207)

* Disable core-js on Next.js core files as it's not transforming anything important

* Move babel options to taskr plugin

* Disable transform-runtime for pages dir

* Disable correctly

* Disable corejs for core files

* Temporarily check if this fixes the error

* Use builtIns and exclude async-to-generator

* Update index.test.js
---
 packages/next/client/router.ts                 |  2 +-
 packages/next/taskfile-babel.js                | 11 ++++++++---
 test/integration/size-limit/test/index.test.js |  4 ++--
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/packages/next/client/router.ts b/packages/next/client/router.ts
index 32da8433124f..41d4dad46af9 100644
--- a/packages/next/client/router.ts
+++ b/packages/next/client/router.ts
@@ -138,7 +138,7 @@ export function makePublicRouterInstance(router: Router): NextRouter {
 
   for (const property of urlPropertyFields) {
     if (typeof _router[property] === 'object') {
-      instance[property] = { ..._router[property] } // makes sure query is not stateful
+      instance[property] = Object.assign({}, _router[property]) // makes sure query is not stateful
       continue
     }
 
diff --git a/packages/next/taskfile-babel.js b/packages/next/taskfile-babel.js
index 0036821f8abb..d31ced3d8bde 100644
--- a/packages/next/taskfile-babel.js
+++ b/packages/next/taskfile-babel.js
@@ -15,10 +15,15 @@ const babelClientOpts = {
           esmodules: true,
         },
         loose: true,
-        exclude: ['transform-typeof-symbol'],
+        // This is handled by the Next.js webpack config that will run next/babel over the same code.
+        exclude: [
+          'transform-typeof-symbol',
+          'transform-async-to-generator',
+          'transform-spread',
+        ],
       },
     ],
-    '@babel/preset-react',
+    ['@babel/preset-react', { useBuiltIns: true }],
   ],
   plugins: [
     // workaround for @taskr/esnext bug replacing `-import` with `-require(`
@@ -31,7 +36,7 @@ const babelClientOpts = {
 const babelServerOpts = {
   presets: [
     '@babel/preset-typescript',
-    '@babel/preset-react',
+    ['@babel/preset-react', { useBuiltIns: true }],
     [
       '@babel/preset-env',
       {
diff --git a/test/integration/size-limit/test/index.test.js b/test/integration/size-limit/test/index.test.js
index 70fd0d332d00..caedbdff0ec7 100644
--- a/test/integration/size-limit/test/index.test.js
+++ b/test/integration/size-limit/test/index.test.js
@@ -81,7 +81,7 @@ describe('Production response size', () => {
     )
 
     // These numbers are without gzip compression!
-    const delta = responseSizeKilobytes - 235
+    const delta = responseSizeKilobytes - 233
     expect(delta).toBeLessThanOrEqual(0) // don't increase size
     expect(delta).toBeGreaterThanOrEqual(-1) // don't decrease size without updating target
   })
@@ -101,7 +101,7 @@ describe('Production response size', () => {
     )
 
     // These numbers are without gzip compression!
-    const delta = responseSizeKilobytes - 203
+    const delta = responseSizeKilobytes - 202
     expect(delta).toBeLessThanOrEqual(0) // don't increase size
     expect(delta).toBeGreaterThanOrEqual(-1) // don't decrease size without updating target
   })