fix(gatsby): more reliable way to use prod versions of react/react-dom (

#29683)

back port of #29620 to v2

Fix #28138 (comment)

Set `NODE_ENV` to `production` in the child worker that does the SSR in dev.

Co-authored-by: Ward Peeters <ward@coding-tech.com>
Co-authored-by: Matt Kane <matt@gatsbyjs.com>

packages/gatsby/src/utils/dev-ssr/render-dev-html.ts

@@ -2,6 +2,7 @@ import JestWorker from "jest-worker"
 import fs from "fs-extra"
 import { joinPath } from "gatsby-core-utils"
 import report from "gatsby-cli/lib/reporter"
+import { isCI } from "gatsby-core-utils"
 
 import { startListener } from "../../bootstrap/requires-writer"
 import { findPageByPath } from "../find-page-by-path"
@@ -13,7 +14,15 @@ const startWorker = (): any => {
   const newWorker = new JestWorker(require.resolve(`./render-dev-html-child`), {
     exposedMethods: [`renderHTML`, `deleteModuleCache`, `warmup`],
     numWorkers: 1,
-    forkOptions: { silent: false },
+    forkOptions: {
+      silent: false,
+      env: {
+        ...process.env,
+        NODE_ENV: isCI() ? `production` : `development`,
+        forceColors: true,
+        GATSBY_EXPERIMENTAL_DEV_SSR: true,
+      },
+    },
   })
 
   // jest-worker is lazy with forking but we want to fork immediately so the user

packages/gatsby/src/utils/webpack.config.js

@@ -697,23 +697,6 @@ module.exports = async (
 
     config.externals = [
       function (context, request, callback) {
-        if (
-          stage === `develop-html` &&
-          isCI() &&
-          process.env.GATSBY_EXPERIMENTAL_DEV_SSR
-        ) {
-          if (request === `react`) {
-            callback(null, `react/cjs/react.production.min.js`)
-            return
-          } else if (request === `react-dom/server`) {
-            callback(
-              null,
-              `react-dom/cjs/react-dom-server.node.production.min.js`
-            )
-            return
-          }
-        }
-
         const external = isExternal(request)
         if (external !== null) {
           callback(null, external)