Proxy server loader errors through serverLoader during hydration

.changeset/server-loader-error.md

@@ -0,0 +1,5 @@
+---
+"@remix-run/react": patch
+---
+
+Propagate server `loader` errors through `serverLoader` in hydrating `clientLoader`'s

integration/client-data-test.ts

@@ -1,5 +1,6 @@
 import { test, expect } from "@playwright/test";
 
+import { ServerMode } from "../packages/remix-server-runtime/mode.js";
 import {
   createAppFixture,
   createFixture,
@@ -724,6 +725,61 @@ test.describe("Client Data", () => {
       html = await app.getHtml("main");
       expect(html).toMatch("Child Server Loader Data (2+) (mutated by client)");
     });
+
+    test("server loader errors are re-thrown from serverLoader()", async ({
+      page,
+    }) => {
+      let _consoleError = console.error;
+      console.error = () => {};
+      appFixture = await createAppFixture(
+        await createFixture(
+          {
+            files: {
+              ...getFiles({
+                parentClientLoader: false,
+                parentClientLoaderHydrate: false,
+                childClientLoader: false,
+                childClientLoaderHydrate: false,
+              }),
+              "app/routes/parent.child.tsx": js`
+                import { ClientLoaderFunctionArgs, useRouteError } from "@remix-run/react";
+
+                export function loader() {
+                  throw new Error("Broken!")
+                }
+
+                export async function clientLoader({ serverLoader }) {
+                  return await serverLoader();
+                }
+                clientLoader.hydrate = true;
+
+                export default function Index() {
+                  return <h1>Should not see me</h1>;
+                }
+
+                export function ErrorBoundary() {
+                  let error = useRouteError();
+                  return <p id="child-error">{error.message}</p>;
+                }
+              `,
+            },
+          },
+          ServerMode.Development // Avoid error sanitization
+        ),
+        ServerMode.Development // Avoid error sanitization
+      );
+      let app = new PlaywrightFixture(appFixture, page);
+
+      await app.goto("/parent/child");
+      let html = await app.getHtml("main");
+      expect(html).toMatch("Broken!");
+      // Ensure we hydrate and remain on the boundary
+      await new Promise((r) => setTimeout(r, 100));
+      html = await app.getHtml("main");
+      expect(html).toMatch("Broken!");
+      expect(html).not.toMatch("Should not see me");
+      console.error = _consoleError;
+    });
   });
 
   test.describe("clientLoader - lazy route module", () => {

packages/remix-react/routes.tsx

@@ -227,15 +227,11 @@ export function createClientRoutes(
           : routeModule.shouldRevalidate,
       });
 
-      let initialData =
-        initialState &&
-        initialState.loaderData &&
-        initialState.loaderData[route.id];
-
+      let initialData = initialState?.loaderData?.[route.id];
+      let initialError = initialState?.errors?.[route.id];
       let isHydrationRequest =
         needsRevalidation == null &&
-        routeModule.clientLoader != null &&
-        (routeModule.clientLoader.hydrate === true || !route.hasLoader);
+        (routeModule.clientLoader?.hydrate === true || !route.hasLoader);
 
       dataRoute.loader = async ({ request, params }: LoaderFunctionArgs) => {
         try {
@@ -253,8 +249,11 @@ export function createClientRoutes(
                   throw getNoServerHandlerError("loader", route.id);
                 }
 
-                // On the first call, resolve with the pre-loaded server data
+                // On the first call, resolve with the server result
                 if (isHydrationRequest) {
+                  if (initialError !== undefined) {
+                    throw initialError;
+                  }
                   return initialData;
                 }