fix(file-router): enable server fallback with client layout and empty client routes (#3280) (CP: 24.6)

packages/ts/file-router/src/runtime/RouterConfigurationBuilder.ts

@@ -23,11 +23,7 @@ interface RouteBase {
   children?: readonly this[];
 }
 
-function isReactRouteModule(module?: Module): module is RouteModule<ComponentType> | undefined {
-  if (!module) {
-    return true;
-  }
-
+function isReactRouteModule(module: Module): module is RouteModule<ComponentType> {
   return (
     ('default' in module && typeof module.default === 'function') ||
     ('config' in module && typeof module.config === 'object')
@@ -94,7 +90,7 @@ export class RouterConfigurationBuilder {
     return this.update(routes, ({ original, overriding: added, children }) => {
       if (added) {
         const { module, path, flowLayout } = added;
-        if (!isReactRouteModule(module)) {
+        if (module && !isReactRouteModule(module)) {
           throw new Error(
             `The module for the "${path}" section doesn't have the React component exported by default or a ViewConfig object exported as "config"`,
           );
@@ -210,14 +206,14 @@ export class RouterConfigurationBuilder {
             if (flag === true) {
               lists.server.push({
                 ...route,
-                children: server.length + ambivalent.length > 0 ? [...server, ...ambivalent] : undefined,
+                children: route.children ? [...server, ...ambivalent] : undefined,
               } as RouteObject);
             } else if (server.length > 0) {
               // Even if the route doesn't have the flag, it goes to the server
               // list if any of the children has the flag enabled.
               lists.server.push({
                 ...route,
-                children: server,
+                children: route.children ? server : undefined,
               } as RouteObject);
             }
 
@@ -227,7 +223,7 @@ export class RouterConfigurationBuilder {
             if (flag === false || client.length > 0) {
               lists.client.push({
                 ...route,
-                children: client.length > 0 ? client : undefined,
+                children: route.children ? client : undefined,
               } as RouteObject);
             }
 
@@ -240,7 +236,7 @@ export class RouterConfigurationBuilder {
             ) {
               lists.ambivalent.push({
                 ...route,
-                children: ambivalent.length > 0 ? ambivalent : undefined,
+                children: route.children ? ambivalent : undefined,
               } as RouteObject);
             }
 

packages/ts/file-router/test/runtime/RouterConfigurationBuilder.spec.tsx

@@ -30,6 +30,10 @@ describe('RouterBuilder', () => {
     return <></>;
   }
 
+  function Layout() {
+    return <></>;
+  }
+
   beforeEach(() => {
     builder = new RouterConfigurationBuilder().withReactRoutes([
       {
@@ -944,4 +948,34 @@ describe('RouterBuilder', () => {
       ]);
     });
   });
+
+  it('should support file routes with only client layout and server fallback', () => {
+    const { routes } = new RouterConfigurationBuilder()
+      .withFileRoutes([
+        {
+          path: '',
+          module: {
+            default: Layout,
+          },
+          children: [],
+        },
+      ])
+      .withFallback(Server)
+      .build();
+
+    expect(routes).to.be.like([
+      {
+        path: '',
+        handle: {
+          title: 'Layout',
+        },
+        children: [
+          { path: '*', element: <Server /> },
+          { index: true, element: <Server /> },
+        ],
+      },
+      { path: '*', element: <Server /> },
+      { index: true, element: <Server /> },
+    ]);
+  });
 });