fix(router): adjust setting navigationTransition when a new navigation cancels an existing one (#29636)

Prior to this change, if a navigation was ongoing and a new one came in, the router could get into a state where `router.currentNavigation` was `null` even though a navigation was executing. This change moves where we set the `currentNavigation` value so it's inside a `switchMap`. This solves the problem because the `finally` on the `switchMap` had been setting `currentNavigation` to `null` but the new `currentNavigation` value would have already been set. Essentially this was a timing problem and is resolved with this change.

Fixes #29389 #29590

PR Close #29636

packages/router/src/router.ts

@@ -452,6 +452,11 @@ export class Router {
               ...t, extractedUrl: this.urlHandlingStrategy.extract(t.rawUrl)
             } as NavigationTransition)),
 
+        // Using switchMap so we cancel executing navigations when a new one comes in
+        switchMap(t => {
+          let completed = false;
+          let errored = false;
+          return of (t).pipe(
               // Store the Navigation object
               tap(t => {
                 this.currentNavigation = {
@@ -465,12 +470,6 @@ export class Router {
                       null
                 };
               }),
-
-        // Using switchMap so we cancel executing navigations when a new one comes in
-        switchMap(t => {
-          let completed = false;
-          let errored = false;
-          return of (t).pipe(
               switchMap(t => {
                 const urlTransition =
                     !this.navigated || t.extractedUrl.toString() !== this.browserUrlTree.toString();

packages/router/test/integration.spec.ts

@@ -1067,6 +1067,27 @@ describe('Integration', () => {
        ]);
      })));
 
+  it('should properly set currentNavigation when cancelling in-flight navigations',
+     fakeAsync(inject([Router], (router: Router) => {
+       const fixture = createRoot(router, RootCmp);
+
+       router.resetConfig([{path: 'user/:name', component: UserCmp}]);
+
+       router.navigateByUrl('/user/init');
+       advance(fixture);
+
+       router.navigateByUrl('/user/victor');
+       expect((router as any).currentNavigation).not.toBe(null);
+       router.navigateByUrl('/user/fedor');
+       // Due to https://github.com/angular/angular/issues/29389, this would be `false`
+       // when running a second navigation.
+       expect((router as any).currentNavigation).not.toBe(null);
+       advance(fixture);
+
+       expect((router as any).currentNavigation).toBe(null);
+       expect(fixture.nativeElement).toHaveText('user fedor');
+     })));
+
   it('should handle failed navigations gracefully', fakeAsync(inject([Router], (router: Router) => {
        const fixture = createRoot(router, RootCmp);