Fix usage of Component API within descendant routes (#10434)

Author: brophdawg11

.changeset/descendant-routes-component.md

@@ -0,0 +1,5 @@
+---
+"react-router": patch
+---
+
+Fix usage of `Component` API within descendant `<Routes>`

docs/route/route.md

@@ -62,7 +62,7 @@ const router = createBrowserRouter(
 
 Neither style is discouraged and behavior is identical. For the majority of this doc we will use the JSX style because that's what most people are accustomed to in the context of React Router.
 
-<docs-info>If you do not wish to specify a React element (i.e., `element={<MyComponent />}`) you may specify a `Component` instead (i.e., `Component={MyComponent}`) and React Router will call `createElement` for you internally.</docs-info>
+<docs-info>When using `RouterProvider`, if you do not wish to specify a React element (i.e., `element={<MyComponent />}`) you may specify a `Component` instead (i.e., `Component={MyComponent}`) and React Router will call `createElement` for you internally. You should only do this for `RouterProvider` applications though since using `Component` inside of `<Routes>` will de-optimize React's ability to reuse the created element across renders.</docs-info>
 
 ## Type declaration
 
@@ -312,6 +312,8 @@ Otherwise use `Component` and React Router will create the React Element for you
 <Route path="/for-sale" Component={Properties} />
 ```
 
+<docs-warning>You should only opt into the `Component` API for data routes via `RouterProvider`. Using this API on a `<Route>` inside `<Routes>` will de-optimize React's ability to reuse the created element across renders.</docs-warning>
+
 ## `errorElement`/`ErrorBoundary`
 
 When a route throws an exception while rendering, in a `loader` or in an `action`, this React Element/Component will render instead of the normal `element`/`Component`.

packages/react-router/__tests__/Route-test.tsx

@@ -22,6 +22,25 @@ describe("A <Route>", () => {
     `);
   });
 
+  it("renders its `Component` prop", () => {
+    let renderer: TestRenderer.ReactTestRenderer;
+    TestRenderer.act(() => {
+      renderer = TestRenderer.create(
+        <MemoryRouter initialEntries={["/home"]}>
+          <Routes>
+            <Route path="home" Component={() => <h1>Home</h1>} />
+          </Routes>
+        </MemoryRouter>
+      );
+    });
+
+    expect(renderer.toJSON()).toMatchInlineSnapshot(`
+      <h1>
+        Home
+      </h1>
+    `);
+  });
+
   it("renders its child routes when no `element` prop is given", () => {
     let renderer: TestRenderer.ReactTestRenderer;
     TestRenderer.act(() => {

packages/react-router/lib/hooks.tsx

@@ -689,6 +689,14 @@ export function _renderMatches(
       let children: React.ReactNode;
       if (error) {
         children = errorElement;
+      } else if (match.route.Component) {
+        // Note: This is a de-optimized path since React won't re-use the
+        // ReactElement since it's identity changes with each new
+        // React.createElement call.  We keep this so folks can use
+        // `<Route Component={...}>` in `<Routes>` but generally `Component`
+        // usage is only advised in `RouterProvider` when we can convert it to
+        // `element` ahead of time.
+        children = <match.route.Component />;
       } else if (match.route.element) {
         children = match.route.element;
       } else {