bug: NavController direction gets lost when an Angular route guard returns a UrlTree #31071

Prerequisites

• I have read the Contributing Guidelines.
• I agree to follow the Code of Conduct.
• I have searched for existing issues that already report this problem, without success.

Ionic Framework Version

v8.x

Current Behavior

When using NavController.navigateRoot and an Angular Route Guard returns a UrlTree, the existing pages in the navigation stack remain.

Expected Behavior

When using NavController.navigateRoot and an Angular Route Guard returns a UrlTree, the existing pages in the navigation stack are removed.

Steps to Reproduce

1. Install @ionic/angular and @ionic/core >= 8.7.18
2. Setup an Angular route with a Route Guard that returns a UrlTree
3. Use NavController.navigateRoot to navigate to that route
4. Check the navigation stack, for example with IonRouterOutlet.canGoBack

Code Reproduction URL

ca03a6d

Ionic Info

Ionic:

Ionic CLI : 6.20.1
Ionic Framework : not installed
@angular-devkit/build-angular : 21.2.2
@angular-devkit/schematics : 21.2.2
@angular/cli : 21.2.2
@ionic/angular-toolkit : not installed

Capacitor:

Capacitor CLI : 8.1.0
@capacitor/android : 8.1.0
@capacitor/core : 8.1.0
@capacitor/ios : 8.1.0

Utility:

cordova-res : not installed globally
native-run : not installed globally

System:

NodeJS : v22.22.0
npm : 10.9.4
OS : macOS

Additional Information

The issue was introduced in Ionic 8.7.18 with #30955. Because of that PR, a NavigationCancel leads to the NavController direction being lost. This is not necessarily bad, but it interacts poorly with Angular Route Guard redirects. When such a Route Guard returns a UrlTree, the initial navigation gets cancelled and a new navigation to that UrlTree gets started. Unfortunately, that new navigation loses the information about the NavController direction because of the intermittent NavigationCancel.

Preferred solution:
Detect whether the NavigationCancel was caused by a Route Guard redirecting somewhere else and in those cases retain the NavController direction.

Alternative solution:
If our preferred solution is not feasible, please provide guidance on how to achieve the intended outcome. In our case: Start a navigation such that if the Route Guards lead to a successful navigation, the rest of the navigation stack is removed.