core-app-api: add isReactRouterBeta and select traversal mode

Co-authored-by: blam <ben@blam.sh>
Co-authored-by: Fredrik Adelöw <freben@gmail.com>
Co-authored-by: Johan Haals <johan.haals@gmail.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/core-app-api/src/app/AppManager.tsx

@@ -81,6 +81,7 @@ import { defaultConfigLoader } from './defaultConfigLoader';
 import { ApiRegistry } from '../apis/system/ApiRegistry';
 import { resolveRouteBindings } from './resolveRouteBindings';
 import { BackstageRouteObject } from '../routing/types';
+import { isReactRouterBeta } from './isReactRouterBeta';
 
 type CompatiblePlugin =
   | BackstagePlugin
@@ -224,7 +225,9 @@ export class AppManager implements BackstageApp {
           root: children,
           discoverers: [childDiscoverer, routeElementDiscoverer],
           collectors: {
-            routing: routingV2Collector,
+            routing: isReactRouterBeta()
+              ? routingV1Collector
+              : routingV2Collector,
             collectedPlugins: pluginCollector,
             featureFlags: featureFlagCollector,
           },

packages/core-app-api/src/app/isReactRouterBeta.test.tsx

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+describe.each(['beta', 'stable'])('react-router %s', rrVersion => {
+  it('should return the correct value for the different version', () => {
+    jest.isolateModules(() => {
+      jest.doMock('react-router-dom', () =>
+        rrVersion === 'beta'
+          ? jest.requireActual('react-router-dom-beta')
+          : jest.requireActual('react-router-dom-stable'),
+      );
+
+      const { isReactRouterBeta } = require('./isReactRouterBeta');
+      expect(isReactRouterBeta()).toBe(rrVersion === 'beta');
+    });
+  });
+});
+
+// eslint-disable-next-line jest/no-export
+export {};

packages/core-app-api/src/app/isReactRouterBeta.tsx

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import React from 'react';
+import { createRoutesFromChildren, Route } from 'react-router-dom';
+
+export function isReactRouterBeta(): boolean {
+  const [obj] = createRoutesFromChildren(<Route index element={<div />} />);
+  return !obj.index;
+}