From feb9173734c4f053f1e208063146b79ed5ca8a3e Mon Sep 17 00:00:00 2001
From: Mark Dalgleish <mark.john.dalgleish@gmail.com>
Date: Fri, 5 Sep 2025 11:40:52 +1000
Subject: [PATCH] Validate unsupported config in RSC Framework Mode

---
 packages/react-router-dev/config/config.ts   | 21 +++++++++++++++-
 packages/react-router-dev/vite/rsc/plugin.ts | 26 +++++++++++++++++++-
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/packages/react-router-dev/config/config.ts b/packages/react-router-dev/config/config.ts
index 951714b7a4..68ef25cb12 100644
--- a/packages/react-router-dev/config/config.ts
+++ b/packages/react-router-dev/config/config.ts
@@ -83,6 +83,8 @@ type ServerBundlesBuildManifest = BaseBuildManifest & {
 
 type ServerModuleFormat = "esm" | "cjs";
 
+type ValidateConfigFunction = (config: ReactRouterConfig) => string | void;
+
 interface FutureConfig {
   /**
    * Enable route middleware
@@ -356,11 +358,13 @@ async function resolveConfig({
   viteNodeContext,
   reactRouterConfigFile,
   skipRoutes,
+  validateConfig,
 }: {
   root: string;
   viteNodeContext: ViteNode.Context;
   reactRouterConfigFile?: string;
   skipRoutes?: boolean;
+  validateConfig?: ValidateConfigFunction;
 }): Promise<Result<ResolvedReactRouterConfig>> {
   let reactRouterUserConfig: ReactRouterConfig = {};
 
@@ -383,6 +387,13 @@ async function resolveConfig({
       }
 
       reactRouterUserConfig = configModule.default;
+
+      if (validateConfig) {
+        const error = validateConfig(reactRouterUserConfig);
+        if (error) {
+          return err(error);
+        }
+      }
     } catch (error) {
       return err(`Error loading ${reactRouterConfigFile}: ${error}`);
     }
@@ -631,11 +642,13 @@ export async function createConfigLoader({
   watch,
   mode,
   skipRoutes,
+  validateConfig,
 }: {
   watch: boolean;
   rootDirectory?: string;
   mode: string;
   skipRoutes?: boolean;
+  validateConfig?: ValidateConfigFunction;
 }): Promise<ConfigLoader> {
   root = Path.normalize(root ?? process.env.REACT_ROUTER_ROOT ?? process.cwd());
 
@@ -660,7 +673,13 @@ export async function createConfigLoader({
   updateReactRouterConfigFile();
 
   let getConfig = () =>
-    resolveConfig({ root, viteNodeContext, reactRouterConfigFile, skipRoutes });
+    resolveConfig({
+      root,
+      viteNodeContext,
+      reactRouterConfigFile,
+      skipRoutes,
+      validateConfig,
+    });
 
   let appDirectory: string;
 
diff --git a/packages/react-router-dev/vite/rsc/plugin.ts b/packages/react-router-dev/vite/rsc/plugin.ts
index 9da90a9415..da9cb27168 100644
--- a/packages/react-router-dev/vite/rsc/plugin.ts
+++ b/packages/react-router-dev/vite/rsc/plugin.ts
@@ -43,7 +43,31 @@ export function reactRouterRSCVitePlugin(): Vite.PluginOption[] {
         const rootDirectory = getRootDirectory(viteUserConfig);
         const watch = command === "serve";
 
-        configLoader = await createConfigLoader({ rootDirectory, mode, watch });
+        configLoader = await createConfigLoader({
+          rootDirectory,
+          mode,
+          watch,
+          validateConfig: (userConfig) => {
+            let errors: string[] = [];
+            if (userConfig.buildEnd) errors.push("buildEnd");
+            if (userConfig.prerender) errors.push("prerender");
+            if (userConfig.presets?.length) errors.push("presets");
+            if (userConfig.routeDiscovery) errors.push("routeDiscovery");
+            if (userConfig.serverBundles) errors.push("serverBundles");
+            if (userConfig.ssr === false) errors.push("ssr: false");
+            if (userConfig.future?.unstable_splitRouteModules)
+              errors.push("future.unstable_splitRouteModules");
+            if (userConfig.future?.unstable_viteEnvironmentApi === false)
+              errors.push("future.unstable_viteEnvironmentApi: false");
+            if (userConfig.future?.v8_middleware === false)
+              errors.push("future.v8_middleware: false");
+            if (userConfig.future?.unstable_subResourceIntegrity)
+              errors.push("future.unstable_subResourceIntegrity");
+            if (errors.length) {
+              return `RSC Framework Mode does not currently support the following React Router config:\n${errors.map((x) => ` - ${x}`).join("\n")}\n`;
+            }
+          },
+        });
 
         const configResult = await configLoader.getConfig();
         if (!configResult.ok) throw new Error(configResult.error);