Update error message

Author: timneutkens

packages/next/errors.json

@@ -666,5 +666,7 @@
   "665": "Failed to find Server Action \"%s\". This request might be from an older or newer deployment.\\nRead more: https://nextjs.org/docs/messages/failed-to-find-server-action",
   "666": "Turbopack builds are only available in canary builds of Next.js.",
   "667": "receiveExpiredTags is deprecated, and not expected to be called.",
-  "668": "Internal Next.js error: Router action dispatched before initialization."
+  "668": "Internal Next.js error: Router action dispatched before initialization.",
+  "669": "Invariant: --turbopack is set but the build used Webpack",
+  "670": "Invariant: --turbopack is not set but the build used Turbopack. Add --turbopack to \"next start\"."
 }

packages/next/src/server/next-server.ts

@@ -193,11 +193,11 @@ export default class NextNodeServer extends BaseServer<
 
     if (process.env.TURBOPACK && !isTurbopackBuild) {
       throw new Error(
-        `Invariant: --turbopack is set but the build is not a Turbopack build`
+        `Invariant: --turbopack is set but the build used Webpack`
       )
     } else if (!process.env.TURBOPACK && isTurbopackBuild) {
       throw new Error(
-        `Invariant: --turbopack is not set but the build is a Turbopack build`
+        `Invariant: --turbopack is not set but the build used Turbopack. Add --turbopack to "next start".`
       )
     }