feat: add refresh flag to navigation event (#15324)

Add the isRefreshEvent to BeforeEnterEvent
and AfterNavigationEvent to be make it possible
to distinguish if the event is for a refresh of
a preserve on refresh view.

Fixes #14999

Author: caalador

flow-server/src/main/java/com/vaadin/flow/router/AfterNavigationEvent.java

@@ -73,4 +73,13 @@ public List<HasElement> getActiveChain() {
     public Router getSource() {
         return (Router) super.getSource();
     }
+
+    /**
+     * Check if event is for a refresh of a preserveOnRefresh view.
+     *
+     * @return true if refresh of a preserve on refresh view
+     */
+    public boolean isRefreshEvent() {
+        return event.getTrigger().equals(NavigationTrigger.REFRESH);
+    }
 }

flow-server/src/main/java/com/vaadin/flow/router/BeforeEnterEvent.java

@@ -111,4 +111,13 @@ public BeforeEnterEvent(Router router, NavigationTrigger trigger,
         super(router, trigger, location, navigationTarget, parameters, ui,
                 layouts);
     }
+
+    /**
+     * Check if event is for a refresh of a preserveOnRefresh view.
+     *
+     * @return true if refresh of a preserve on refresh view
+     */
+    public boolean isRefreshEvent() {
+        return getTrigger().equals(NavigationTrigger.REFRESH);
+    }
 }

flow-server/src/main/java/com/vaadin/flow/router/NavigationTrigger.java

@@ -63,5 +63,10 @@ public enum NavigationTrigger {
      *
      * @see com.vaadin.flow.component.internal.JavaScriptBootstrapUI
      */
-    CLIENT_SIDE
+    CLIENT_SIDE,
+
+    /**
+     * Navigation is for a reload event on a preserveOnRefresh route.
+     */
+    REFRESH
 }

flow-server/src/main/java/com/vaadin/flow/router/internal/AbstractNavigationStateRenderer.java

@@ -189,6 +189,13 @@ public int handle(NavigationEvent event) {
             clearAllPreservedChains(ui);
         }
 
+        // Set navigationTrigger to RELOAD if this is a refresh of a preserve
+        // view.
+        if (preserveOnRefreshTarget && !chain.isEmpty()) {
+            event = new NavigationEvent(event.getSource(), event.getLocation(),
+                    event.getUI(), NavigationTrigger.REFRESH);
+        }
+
         // If the navigation is postponed, using BeforeLeaveEvent#postpone,
         // pushing history state shouldn't be done. So, it's done here to make
         // sure that when history state is pushed the navigation is not

flow-server/src/test/java/com/vaadin/flow/router/internal/NavigationStateRendererTest.java

@@ -43,6 +43,11 @@
 import com.vaadin.flow.component.page.Page;
 import com.vaadin.flow.component.page.PendingJavaScriptResult;
 import com.vaadin.flow.dom.Element;
+import com.vaadin.flow.router.AfterNavigationEvent;
+import com.vaadin.flow.router.AfterNavigationObserver;
+import com.vaadin.flow.router.BeforeEnterEvent;
+import com.vaadin.flow.router.BeforeEnterObserver;
+import com.vaadin.flow.router.BeforeLeaveEvent;
 import com.vaadin.flow.router.Location;
 import com.vaadin.flow.router.NavigationEvent;
 import com.vaadin.flow.router.NavigationState;
@@ -82,6 +87,29 @@ private static class PreservedView extends Text {
         }
     }
 
+    @Route(value = "preserved")
+    @PreserveOnRefresh
+    private static class PreservedEventView extends Text
+            implements BeforeEnterObserver, AfterNavigationObserver {
+        static boolean refreshBeforeEnter;
+        static boolean refreshAfterNavigation;
+
+        PreservedEventView() {
+            super("");
+        }
+
+        @Override
+        public void beforeEnter(BeforeEnterEvent event) {
+            refreshBeforeEnter = event.isRefreshEvent();
+        }
+
+        @Override
+        public void afterNavigation(AfterNavigationEvent event) {
+            refreshAfterNavigation = event.isRefreshEvent();
+
+        }
+    }
+
     @Route(value = "regular")
     private static class RegularView extends Text {
         RegularView() {
@@ -324,6 +352,59 @@ public void handle_preserveOnRefreshAndWindowNameKnown_componentIsCachedRetrieve
                         session, new Location("preserved")));
     }
 
+    @Test
+    public void handle_preserveOnRefresh_refreshIsFlaggedInEvent() {
+        // given a service with instantiator
+        MockVaadinServletService service = createMockServiceWithInstantiator();
+
+        // given a locked session
+        MockVaadinSession session = new AlwaysLockedVaadinSession(service);
+        session.setConfiguration(new MockDeploymentConfiguration());
+
+        // given a UI that contain a window name ROOT.123
+        MockUI ui = new MockUI(session);
+        ExtendedClientDetails details = Mockito
+                .mock(ExtendedClientDetails.class);
+        Mockito.when(details.getWindowName()).thenReturn("ROOT.123");
+        ui.getInternals().setExtendedClientDetails(details);
+
+        // given a NavigationStateRenderer mapping to PreservedEventView
+        NavigationStateRenderer renderer = new NavigationStateRenderer(
+                navigationStateFromTarget(PreservedEventView.class));
+
+        // when a navigation event reaches the renderer
+        renderer.handle(new NavigationEvent(new Router(new TestRouteRegistry()),
+                new Location("preserved"), ui, NavigationTrigger.PAGE_LOAD));
+
+        // then the session has a cached record of the view
+        Assert.assertTrue("Session expected to have cached view",
+                AbstractNavigationStateRenderer.getPreservedChain(session,
+                        "ROOT.123", new Location("preserved")).isPresent());
+
+        // given the recently instantiated view
+        final PreservedEventView view = (PreservedEventView) ui.getInternals()
+                .getActiveRouterTargetsChain().get(0);
+        Assert.assertFalse(
+                "Initial view load should not be a refresh for before",
+                view.refreshBeforeEnter);
+        Assert.assertFalse(
+                "Initial view load should not be a refresh for after",
+                view.refreshAfterNavigation);
+
+        // when another navigation targets the same location
+        renderer.handle(new NavigationEvent(new Router(new TestRouteRegistry()),
+                new Location("preserved"), ui, NavigationTrigger.PAGE_LOAD));
+
+        // then the same view is routed to
+        Assert.assertEquals("Expected same view", view,
+                ui.getInternals().getActiveRouterTargetsChain().get(0));
+
+        Assert.assertTrue("Reload should be flagged for before",
+                view.refreshBeforeEnter);
+        Assert.assertTrue("Reload should be flagged for after",
+                view.refreshAfterNavigation);
+    }
+
     @Test
     public void handle_preserveOnRefresh_otherUIChildrenAreMoved() {
         // given a service with instantiator