fix(router): page refresh should not destroy history state (#48540)

The router's `initialNavigation` causes an imperative navigation using
the `navigateByUrl` method. This, however, results in the history state
being removed on a page refresh. This change calls `scheduleNavigation`
directly from `initialNavigation` to ensure the history state is correctly
retained.

PR Close #48540

packages/router/src/events.ts

@@ -19,6 +19,7 @@ import {ActivatedRouteSnapshot, RouterStateSnapshot} from './router_state';
  * @publicApi
  */
 export type NavigationTrigger = 'imperative'|'popstate'|'hashchange';
+export const IMPERATIVE_NAVIGATION = 'imperative';
 
 /**
  * Identifies the type of a router event.

packages/router/src/navigation_transition.ts

@@ -11,7 +11,7 @@ import {BehaviorSubject, combineLatest, EMPTY, Observable, of, Subject} from 'rx
 import {catchError, defaultIfEmpty, filter, finalize, map, switchMap, take, tap} from 'rxjs/operators';
 
 import {createRouterState} from './create_router_state';
-import {Event, GuardsCheckEnd, GuardsCheckStart, NavigationCancel, NavigationCancellationCode, NavigationEnd, NavigationError, NavigationSkipped, NavigationSkippedCode, NavigationStart, NavigationTrigger, ResolveEnd, ResolveStart, RouteConfigLoadEnd, RouteConfigLoadStart, RoutesRecognized} from './events';
+import {Event, GuardsCheckEnd, GuardsCheckStart, IMPERATIVE_NAVIGATION, NavigationCancel, NavigationCancellationCode, NavigationEnd, NavigationError, NavigationSkipped, NavigationSkippedCode, NavigationStart, NavigationTrigger, ResolveEnd, ResolveStart, RouteConfigLoadEnd, RouteConfigLoadStart, RoutesRecognized} from './events';
 import {NavigationBehaviorOptions, QueryParamsHandling, Route, Routes} from './models';
 import {isNavigationCancelingError, isRedirectingNavigationCancelingError, redirectingNavigationError} from './navigation_canceling_error';
 import {activateRoutes} from './operators/activate_routes';
@@ -335,7 +335,7 @@ export class NavigationTransitions {
       resolve: null,
       reject: null,
       promise: Promise.resolve(true),
-      source: 'imperative',
+      source: IMPERATIVE_NAVIGATION,
       restoredState: null,
       currentSnapshot: router.routerState.snapshot,
       targetSnapshot: null,
@@ -726,11 +726,12 @@ export class NavigationTransitions {
                                      isBrowserTriggeredNavigation(overallTransitionState.source)
                                };
 
-                               router.scheduleNavigation(mergedTree, 'imperative', null, extras, {
-                                 resolve: overallTransitionState.resolve,
-                                 reject: overallTransitionState.reject,
-                                 promise: overallTransitionState.promise
-                               });
+                               router.scheduleNavigation(
+                                   mergedTree, IMPERATIVE_NAVIGATION, null, extras, {
+                                     resolve: overallTransitionState.resolve,
+                                     reject: overallTransitionState.reject,
+                                     promise: overallTransitionState.promise
+                                   });
                              }
 
                              /* All other errors should reset to the router's internal URL reference
@@ -764,6 +765,6 @@ export class NavigationTransitions {
   }
 }
 
-export function isBrowserTriggeredNavigation(source: 'imperative'|'popstate'|'hashchange') {
-  return source !== 'imperative';
+export function isBrowserTriggeredNavigation(source: NavigationTrigger) {
+  return source !== IMPERATIVE_NAVIGATION;
 }

packages/router/src/router.ts

@@ -12,7 +12,7 @@ import {Observable, of, SubscriptionLike} from 'rxjs';
 
 import {CreateUrlTreeStrategy} from './create_url_tree_strategy';
 import {RuntimeErrorCode} from './errors';
-import {Event, NavigationTrigger} from './events';
+import {Event, IMPERATIVE_NAVIGATION, NavigationTrigger} from './events';
 import {NavigationBehaviorOptions, OnSameUrlNavigation, Routes} from './models';
 import {Navigation, NavigationExtras, NavigationTransition, NavigationTransitions, RestoredState, UrlCreationOptions} from './navigation_transition';
 import {TitleStrategy} from './page_title_strategy';
@@ -354,7 +354,8 @@ export class Router {
   initialNavigation(): void {
     this.setUpLocationChangeListener();
     if (!this.navigationTransitions.hasRequestedNavigation) {
-      this.navigateByUrl(this.location.path(true), {replaceUrl: true});
+      const state = this.location.getState() as RestoredState;
+      this.navigateToSyncWithBrowser(this.location.path(true), IMPERATIVE_NAVIGATION, state);
     }
   }
 
@@ -374,37 +375,49 @@ export class Router {
           // The `setTimeout` was added in #12160 and is likely to support Angular/AngularJS
           // hybrid apps.
           setTimeout(() => {
-            const extras: NavigationExtras = {replaceUrl: true};
-
-            // TODO: restoredState should always include the entire state, regardless
-            // of navigationId. This requires a breaking change to update the type on
-            // NavigationStart’s restoredState, which currently requires navigationId
-            // to always be present. The Router used to only restore history state if
-            // a navigationId was present.
-
-            // The stored navigationId is used by the RouterScroller to retrieve the scroll
-            // position for the page.
-            const restoredState = event.state?.navigationId ? event.state : null;
-
-            // Separate to NavigationStart.restoredState, we must also restore the state to
-            // history.state and generate a new navigationId, since it will be overwritten
-            if (event.state) {
-              const stateCopy = {...event.state} as Partial<RestoredState>;
-              delete stateCopy.navigationId;
-              delete stateCopy.ɵrouterPageId;
-              if (Object.keys(stateCopy).length !== 0) {
-                extras.state = stateCopy;
-              }
-            }
-
-            const urlTree = this.parseUrl(event['url']!);
-            this.scheduleNavigation(urlTree, source, restoredState, extras);
+            this.navigateToSyncWithBrowser(event['url']!, source, event.state);
           }, 0);
         }
       });
     }
   }
 
+  /**
+   * Schedules a router navigation to synchronize Router state with the browser state.
+   *
+   * This is done as a response to a popstate event and the initial navigation. These
+   * two scenarios represent times when the browser URL/state has been updated and
+   * the Router needs to respond to ensure its internal state matches.
+   */
+  private navigateToSyncWithBrowser(
+      url: string, source: NavigationTrigger, state: RestoredState|undefined) {
+    const extras: NavigationExtras = {replaceUrl: true};
+
+    // TODO: restoredState should always include the entire state, regardless
+    // of navigationId. This requires a breaking change to update the type on
+    // NavigationStart’s restoredState, which currently requires navigationId
+    // to always be present. The Router used to only restore history state if
+    // a navigationId was present.
+
+    // The stored navigationId is used by the RouterScroller to retrieve the scroll
+    // position for the page.
+    const restoredState = state?.navigationId ? state : null;
+
+    // Separate to NavigationStart.restoredState, we must also restore the state to
+    // history.state and generate a new navigationId, since it will be overwritten
+    if (state) {
+      const stateCopy = {...state} as Partial<RestoredState>;
+      delete stateCopy.navigationId;
+      delete stateCopy.ɵrouterPageId;
+      if (Object.keys(stateCopy).length !== 0) {
+        extras.state = stateCopy;
+      }
+    }
+
+    const urlTree = this.parseUrl(url);
+    this.scheduleNavigation(urlTree, source, restoredState, extras);
+  }
+
   /** The current URL. */
   get url(): string {
     return this.serializeUrl(this.currentUrlTree);
@@ -562,7 +575,7 @@ export class Router {
     const urlTree = isUrlTree(url) ? url : this.parseUrl(url);
     const mergedTree = this.urlHandlingStrategy.merge(urlTree, this.rawUrlTree);
 
-    return this.scheduleNavigation(mergedTree, 'imperative', null, extras);
+    return this.scheduleNavigation(mergedTree, IMPERATIVE_NAVIGATION, null, extras);
   }
 
   /**
@@ -687,10 +700,6 @@ export class Router {
 
     let targetPageId: number;
     if (this.canceledNavigationResolution === 'computed') {
-      const isInitialPage = this.currentPageId === 0;
-      if (isInitialPage) {
-        restoredState = this.location.getState() as RestoredState | null;
-      }
       // If the `ɵrouterPageId` exist in the state then `targetpageId` should have the value of
       // `ɵrouterPageId`. This is the case for something like a page refresh where we assign the
       // target id to the previously set value for that page.