Fix a partial hydration bug for routes with no loaders (#11325)

.changeset/partial-hydration-no-loader.md

@@ -0,0 +1,5 @@
+---
+"@remix-run/router": patch
+---
+
+Fix a `future.v7_partialHydration` bug that would consider the router uninitialized if a route did not have a loader

packages/router/__tests__/route-fallback-test.ts

@@ -515,4 +515,45 @@ describe("future.v7_partialHydration", () => {
       consoleWarnSpy.mockReset();
     });
   });
+
+  it("does not kick off initial data load for routes that don't have loaders", async () => {
+    let consoleWarnSpy = jest
+      .spyOn(console, "warn")
+      .mockImplementation(() => {});
+    let parentDfd = createDeferred();
+    let parentSpy = jest.fn(() => parentDfd.promise);
+    let router = createRouter({
+      history: createMemoryHistory({ initialEntries: ["/child"] }),
+      routes: [
+        {
+          path: "/",
+          loader: parentSpy,
+          children: [
+            {
+              path: "child",
+            },
+          ],
+        },
+      ],
+      future: {
+        v7_partialHydration: true,
+      },
+      hydrationData: {
+        loaderData: {
+          "0": "PARENT DATA",
+        },
+      },
+    });
+    expect(router.state).toMatchObject({
+      // already initialized so calling initialize() won't kick off loaders
+      initialized: true,
+      navigation: IDLE_NAVIGATION,
+      loaderData: {
+        "0": "PARENT DATA",
+      },
+    });
+
+    router.dispose();
+    consoleWarnSpy.mockReset();
+  });
 });

packages/router/router.ts

@@ -833,11 +833,17 @@ export function createRouter(init: RouterInit): Router {
     // were marked for explicit hydration
     let loaderData = init.hydrationData ? init.hydrationData.loaderData : null;
     let errors = init.hydrationData ? init.hydrationData.errors : null;
-    let isRouteInitialized = (m: AgnosticDataRouteMatch) =>
-      m.route.loader &&
-      m.route.loader.hydrate !== true &&
-      ((loaderData && loaderData[m.route.id] !== undefined) ||
-        (errors && errors[m.route.id] !== undefined));
+    let isRouteInitialized = (m: AgnosticDataRouteMatch) => {
+      // No loader, nothing to initialize
+      if (!m.route.loader) return true;
+      // Explicitly opting-in to running on hydration
+      if (m.route.loader.hydrate === true) return false;
+      // Otherwise, initialized if hydrated with data or an error
+      return (
+        (loaderData && loaderData[m.route.id] !== undefined) ||
+        (errors && errors[m.route.id] !== undefined)
+      );
+    };
 
     // If errors exist, don't consider routes below the boundary
     if (errors) {