feat(gatsby): remove concurrent-features flag and depend on export (#31818) (#31830)

(cherry picked from commit 34b6d47)

Co-authored-by: Ward Peeters <[email protected]>

Author: GatsbyJS Bot

packages/gatsby/cache-dir/app.js

@@ -31,15 +31,6 @@ module.hot.accept([
 
 window.___emitter = emitter
 
-if (
-  process.env.GATSBY_EXPERIMENTAL_CONCURRENT_FEATURES &&
-  !ReactDOM.createRoot
-) {
-  throw new Error(
-    `The GATSBY_EXPERIMENTAL_CONCURRENT_FEATURES flag is not compatible with your React version. Please install "[email protected]" and "[email protected]" or higher.`
-  )
-}
-
 const loader = new DevLoader(asyncRequires, matchPaths)
 setLoader(loader)
 loader.setApiRunner(apiRunner)
@@ -141,10 +132,7 @@ apiRunnerAsync(`onClientEntry`).then(() => {
   // render to avoid React complaining about hydration mis-matches.
   let defaultRenderer = ReactDOM.render
   if (focusEl && focusEl.children.length) {
-    if (
-      process.env.GATSBY_EXPERIMENTAL_CONCURRENT_FEATURES &&
-      ReactDOM.createRoot
-    ) {
+    if (ReactDOM.createRoot) {
       defaultRenderer = ReactDOM.createRoot
     } else {
       defaultRenderer = ReactDOM.hydrate
@@ -208,7 +196,10 @@ apiRunnerAsync(`onClientEntry`).then(() => {
             <LoadingIndicatorEventHandler />
           )
         } else {
-          renderer(<LoadingIndicatorEventHandler />, indicatorMountElement)
+          ReactDOM.render(
+            <LoadingIndicatorEventHandler />,
+            indicatorMountElement
+          )
         }
       }
     }

packages/gatsby/cache-dir/production-app.js

@@ -193,9 +193,7 @@ apiRunnerAsync(`onClientEntry`).then(() => {
     const renderer = apiRunner(
       `replaceHydrateFunction`,
       undefined,
-      process.env.GATSBY_EXPERIMENTAL_CONCURRENT_FEATURES
-        ? ReactDOM.createRoot
-        : ReactDOM.hydrate
+      ReactDOM.createRoot ? ReactDOM.createRoot : ReactDOM.hydrate
     )[0]
 
     domReady(() => {

packages/gatsby/src/utils/flags.ts

@@ -182,30 +182,6 @@ const activeFlags: Array<IFlag> = [
     umbrellaIssue: `https://gatsby.dev/functions-feedback`,
     testFitness: (): fitnessEnum => `LOCKED_IN`,
   },
-  {
-    name: `CONCURRENT_FEATURES`,
-    env: `GATSBY_EXPERIMENTAL_CONCURRENT_FEATURES`,
-    command: `all`,
-    telemetryId: `ConcurrentFeatures`,
-    experimental: true,
-    description: `Enable React's concurrent features`,
-    // umbrellaIssue: `https://gatsby.dev/concurrent-features`,
-    testFitness: (): fitnessEnum => {
-      // Because of this, this flag will never show up
-      const semverConstraints = {
-        react: `^0.0.0-experimental-2bf4805e4`,
-        "react-dom": `^0.0.0-experimental-2bf4805e4`,
-      }
-
-      if (satisfiesSemvers(semverConstraints)) {
-        return true
-      } else {
-        // react & react-dom is either not installed or not new enough so
-        // just disable — it won't work anyways.
-        return false
-      }
-    },
-  },
   {
     name: `LMDB_STORE`,
     env: `GATSBY_EXPERIMENTAL_LMDB_STORE`,