fix(react): improve handling of routes nested under path="/" (#14821)

We noticed this in Sentry's `/issues/:groupId/` route, which uses SDK
v8.43.0. The full route tree is complex, but the relevant parts are:

```js
<Route path="/" element={<div>root</div>}>
  <Route path="/issues/:groupId/" element={<div>issues group</div>}>
    <Route index element={<div>index</div>} />
  </Route>
</Route>
```

If you navigate to e.g. `/issues/123` (no trailing slash), the recorded
transaction name is `//issues/:groupId/` (notice the double slash). This
looks messy but doesn't have too much of a consequence.

The worse issue is when you navigate to e.g. `/issues/123/` (with
trailing slash), the transaction name is `/issues/123/` - it is not
parameterized. This breaks transaction grouping. On the `master` and
`develop` branch of the SDK, the transaction name is recorded as `/`.
This causes the transactions to be grouped incorrectly with the root, as
well as any other routes nested under a route with `path="/"`.

(Thanks @JoshFerge for noticing the bad data in Sentry! 🙌)

---

Note that this commit effectively reverts a change from #14304 where

```js
if (basename + branch.pathname === location.pathname) {
```

became

```js
if (location.pathname.endsWith(basename + branch.pathname)) {
```

This is the change that caused the difference in results between SDK
versions. This will always match when `basename` is empty,
`branch.pathname` is `/`, and `location.pathname` ends with `/` - in
other words, if you have a parent route with `path="/"`, every request
ending in a slash will match it instead of the more specific child
route. (Depending on how often this kind of `Route` nesting happens in
the wild, this could be a wide regression in transaction names.) But, no
tests failed from the removal of `endsWith`. @onurtemizkan, who wrote
the change in question:

> I'd expect this to break descendant routes. But in the final
> implementation, descendant routes don't end up here. So, I
> believe it's safe to revert.

packages/react/src/reactrouterv6-compat-utils.tsx

@@ -427,10 +427,10 @@ function getNormalizedName(
         // If path is not a wildcard and has no child routes, append the path
         if (path && !pathIsWildcardAndHasChildren(path, branch)) {
           const newPath = path[0] === '/' || pathBuilder[pathBuilder.length - 1] === '/' ? path : `/${path}`;
-          pathBuilder += newPath;
+          pathBuilder = trimSlash(pathBuilder) + prefixWithSlash(newPath);
 
           // If the path matches the current location, return the path
-          if (location.pathname.endsWith(basename + branch.pathname)) {
+          if (trimSlash(location.pathname) === trimSlash(basename + branch.pathname)) {
             if (
               // If the route defined on the element is something like
               // <Route path="/stores/:storeId/products/:productId" element={<div>Product</div>} />

packages/react/test/reactrouterv6.test.tsx

@@ -594,6 +594,84 @@ describe('reactRouterV6BrowserTracingIntegration', () => {
       });
     });
 
+    it('works under a slash route with a trailing slash', () => {
+      const client = createMockBrowserClient();
+      setCurrentClient(client);
+
+      client.addIntegration(
+        reactRouterV6BrowserTracingIntegration({
+          useEffect: React.useEffect,
+          useLocation,
+          useNavigationType,
+          createRoutesFromChildren,
+          matchRoutes,
+        }),
+      );
+      const SentryRoutes = withSentryReactRouterV6Routing(Routes);
+
+      render(
+        <MemoryRouter initialEntries={['/']}>
+          <SentryRoutes>
+            <Route index element={<Navigate to="/issues/123/" />} />
+            <Route path="/" element={<div>root</div>}>
+              <Route path="/issues/:groupId/" element={<div>issues group</div>}>
+                <Route index element={<div>index</div>} />
+              </Route>
+            </Route>
+          </SentryRoutes>
+        </MemoryRouter>,
+      );
+
+      expect(mockStartBrowserTracingNavigationSpan).toHaveBeenCalledTimes(1);
+      expect(mockStartBrowserTracingNavigationSpan).toHaveBeenLastCalledWith(expect.any(BrowserClient), {
+        name: '/issues/:groupId/',
+        attributes: {
+          [SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'route',
+          [SEMANTIC_ATTRIBUTE_SENTRY_OP]: 'navigation',
+          [SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN]: 'auto.navigation.react.reactrouter_v6',
+        },
+      });
+    });
+
+    it('works nested under a slash root without a trailing slash', () => {
+      const client = createMockBrowserClient();
+      setCurrentClient(client);
+
+      client.addIntegration(
+        reactRouterV6BrowserTracingIntegration({
+          useEffect: React.useEffect,
+          useLocation,
+          useNavigationType,
+          createRoutesFromChildren,
+          matchRoutes,
+        }),
+      );
+      const SentryRoutes = withSentryReactRouterV6Routing(Routes);
+
+      render(
+        <MemoryRouter initialEntries={['/']}>
+          <SentryRoutes>
+            <Route index element={<Navigate to="/issues/123" />} />
+            <Route path="/" element={<div>root</div>}>
+              <Route path="/issues/:groupId/" element={<div>issues group</div>}>
+                <Route index element={<div>index</div>} />
+              </Route>
+            </Route>
+          </SentryRoutes>
+        </MemoryRouter>,
+      );
+
+      expect(mockStartBrowserTracingNavigationSpan).toHaveBeenCalledTimes(1);
+      expect(mockStartBrowserTracingNavigationSpan).toHaveBeenLastCalledWith(expect.any(BrowserClient), {
+        name: '/issues/:groupId/',
+        attributes: {
+          [SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'route',
+          [SEMANTIC_ATTRIBUTE_SENTRY_OP]: 'navigation',
+          [SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN]: 'auto.navigation.react.reactrouter_v6',
+        },
+      });
+    });
+
     it("updates the scope's `transactionName` on a navigation", () => {
       const client = createMockBrowserClient();
       setCurrentClient(client);
@@ -1397,6 +1475,84 @@ describe('reactRouterV6BrowserTracingIntegration', () => {
       expect(mockRootSpan.setAttribute).toHaveBeenCalledWith(SEMANTIC_ATTRIBUTE_SENTRY_SOURCE, 'route');
     });
 
+    it('works under a slash route with a trailing slash', () => {
+      const client = createMockBrowserClient();
+      setCurrentClient(client);
+
+      client.addIntegration(
+        reactRouterV6BrowserTracingIntegration({
+          useEffect: React.useEffect,
+          useLocation,
+          useNavigationType,
+          createRoutesFromChildren,
+          matchRoutes,
+        }),
+      );
+      const SentryRoutes = withSentryReactRouterV6Routing(Routes);
+
+      render(
+        <MemoryRouter initialEntries={['/']}>
+          <SentryRoutes>
+            <Route index element={<Navigate to="/issues/123/" />} />
+            <Route path="/" element={<div>root</div>}>
+              <Route path="/issues/:groupId/" element={<div>issues group</div>}>
+                <Route index element={<div>index</div>} />
+              </Route>
+            </Route>
+          </SentryRoutes>
+        </MemoryRouter>,
+      );
+
+      expect(mockStartBrowserTracingNavigationSpan).toHaveBeenCalledTimes(1);
+      expect(mockStartBrowserTracingNavigationSpan).toHaveBeenLastCalledWith(expect.any(BrowserClient), {
+        name: '/issues/:groupId/',
+        attributes: {
+          [SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'route',
+          [SEMANTIC_ATTRIBUTE_SENTRY_OP]: 'navigation',
+          [SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN]: 'auto.navigation.react.reactrouter_v6',
+        },
+      });
+    });
+
+    it('works nested under a slash root without a trailing slash', () => {
+      const client = createMockBrowserClient();
+      setCurrentClient(client);
+
+      client.addIntegration(
+        reactRouterV6BrowserTracingIntegration({
+          useEffect: React.useEffect,
+          useLocation,
+          useNavigationType,
+          createRoutesFromChildren,
+          matchRoutes,
+        }),
+      );
+      const SentryRoutes = withSentryReactRouterV6Routing(Routes);
+
+      render(
+        <MemoryRouter initialEntries={['/']}>
+          <SentryRoutes>
+            <Route index element={<Navigate to="/issues/123" />} />
+            <Route path="/" element={<div>root</div>}>
+              <Route path="/issues/:groupId/" element={<div>issues group</div>}>
+                <Route index element={<div>index</div>} />
+              </Route>
+            </Route>
+          </SentryRoutes>
+        </MemoryRouter>,
+      );
+
+      expect(mockStartBrowserTracingNavigationSpan).toHaveBeenCalledTimes(1);
+      expect(mockStartBrowserTracingNavigationSpan).toHaveBeenLastCalledWith(expect.any(BrowserClient), {
+        name: '/issues/:groupId/',
+        attributes: {
+          [SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'route',
+          [SEMANTIC_ATTRIBUTE_SENTRY_OP]: 'navigation',
+          [SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN]: 'auto.navigation.react.reactrouter_v6',
+        },
+      });
+    });
+
     it("updates the scope's `transactionName` on a navigation", () => {
       const client = createMockBrowserClient();
       setCurrentClient(client);