Returning `UrlTree` from a guard was a convenient new feature added to
the `Router`. However, it does not have feature-parity with the old
`router.navigate(...); return false;` pattern. The most common use-case
for this feature is to redirect to a new page _without_ updating the URL
from the initially attempted navigation. For example, rendering a 404
page when the user does not have access privelages to a route.
Fixes#17004Fixes#27148
BREAKING CHANGE: Guards can now return `RedirectCommand` for redirects
in addition to `UrlTree`. Code which expects only `boolean` or `UrlTree`
values in `Route` types will need to be adjusted.
PR Close#45023
`isNavigationCancelingError` & `isRedirectingNavigationCancelingError` had duplicate implementations. This commit also cleans-up those functions.
PR Close#53762
Andrew Scott