fix(vue): Don't call next in Vue router 4 instrumentation (#8351)

Vue Router 4 no longer exposes a `next` resolver function to call inside a `beforeEach` [router guard callback](https://router.vuejs.org/guide/advanced/navigation-guards.html#global-before-guards).
Instead it will resolve the hook when the callback function returns.

This PR checks if `next` is available and only calls it then. Also it
adjusts the types accordingly and adds a test that previously failed.

fixes #8349

packages/vue/src/router.ts

@@ -39,7 +39,7 @@ export type Route = {
 
 interface VueRouter {
   onError: (fn: (err: Error) => void) => void;
-  beforeEach: (fn: (to: Route, from: Route, next: () => void) => void) => void;
+  beforeEach: (fn: (to: Route, from: Route, next?: () => void) => void) => void;
 }
 
 /**
@@ -129,7 +129,12 @@ export function vueRouterInstrumentation(
         });
       }
 
-      next();
+      // Vue Router 4 no longer exposes the `next` function, so we need to
+      // check if it's available before calling it.
+      // `next` needs to be called in Vue Router 3 so that the hook is resolved.
+      if (next) {
+        next();
+      }
     });
   };
 }

packages/vue/test/router.test.ts

@@ -9,7 +9,7 @@ const captureExceptionSpy = jest.spyOn(SentryBrowser, 'captureException');
 
 const mockVueRouter = {
   onError: jest.fn<void, [(error: Error) => void]>(),
-  beforeEach: jest.fn<void, [(from: Route, to: Route, next: () => void) => void]>(),
+  beforeEach: jest.fn<void, [(from: Route, to: Route, next?: () => void) => void]>(),
 };
 
 const mockStartTransaction = jest.fn();
@@ -324,4 +324,30 @@ describe('vueRouterInstrumentation()', () => {
       expect(mockStartTransaction).toHaveBeenCalledTimes(expectedCallsAmount + 1);
     },
   );
+
+  it("doesn't throw when `next` is not available in the beforeEach callback (Vue Router 4)", () => {
+    const instrument = vueRouterInstrumentation(mockVueRouter, { routeLabel: 'path' });
+    instrument(mockStartTransaction, true, true);
+    const beforeEachCallback = mockVueRouter.beforeEach.mock.calls[0][0];
+
+    const from = testRoutes.normalRoute1;
+    const to = testRoutes.namedRoute;
+    beforeEachCallback(to, from, undefined);
+
+    // first startTx call happens when the instrumentation is initialized (for pageloads)
+    expect(mockStartTransaction).toHaveBeenLastCalledWith({
+      name: '/login',
+      metadata: {
+        source: 'route',
+      },
+      data: {
+        params: to.params,
+        query: to.query,
+      },
+      op: 'navigation',
+      tags: {
+        'routing.instrumentation': 'vue-router',
+      },
+    });
+  });
 });