fix: ensure route annotation is on component class (#22878) (#22883)

Throws an exception at startup if a Route annotation is put
on a class that does not extend Component.

Fixes #22877

Co-authored-by: Marco Collovati <marco@vaadin.com>

Author: vaadin-bot

flow-server/src/main/java/com/vaadin/flow/server/startup/AbstractRouteRegistryInitializer.java

@@ -81,8 +81,14 @@ protected Set<Class<? extends Component>> validateRouteClasses(
      * @return true if applicable class
      */
     private boolean isApplicableClass(Class<?> clazz) {
-        return clazz.isAnnotationPresent(Route.class)
-                && Component.class.isAssignableFrom(clazz)
+        boolean hasRouteAnnotation = clazz.isAnnotationPresent(Route.class);
+        if (hasRouteAnnotation && !Component.class.isAssignableFrom(clazz)) {
+            throw new InvalidRouteConfigurationException(String.format(
+                    "'%s' declares '@%s' but does not extend '%s'.",
+                    clazz.getCanonicalName(), Route.class.getSimpleName(),
+                    Component.class.getCanonicalName()));
+        }
+        return hasRouteAnnotation
                 && clazz.getAnnotation(Route.class).registerAtStartup();
     }
 

flow-server/src/test/java/com/vaadin/flow/server/startup/AbstractRouteRegistryInitializerTest.java

@@ -117,12 +117,29 @@ public static class AliasesWithSamePath extends Component {
 
     }
 
+    @Route("foo")
+    public static class NonComponent {
+
+    }
+
     @Test(expected = InvalidRouteLayoutConfigurationException.class)
     public void routeAndParentLayout_notRouterLayout_throws() {
         initializer.validateRouteClasses(context,
                 Stream.of(RouteAndParentLayout.class));
     }
 
+    @Test
+    public void validateRouteClasses_annotationOnNonComponentClass_throws() {
+        InvalidRouteConfigurationException exception = Assert.assertThrows(
+                InvalidRouteConfigurationException.class,
+                () -> initializer.validateRouteClasses(context,
+                        Stream.of(NonComponent.class)));
+        Assert.assertTrue(containsQuotedAnnotationName(exception.getMessage(),
+                Route.class));
+        Assert.assertTrue(exception.getMessage()
+                .contains("not extend '" + Component.class.getCanonicalName()));
+    }
+
     @Test
     public void validateRouteClasses_samePathForRouteAndAlias_throws() {
         InvalidRouteConfigurationException exception = Assert.assertThrows(

flow-tests/test-embedding/embedding-test-assets/src/main/java/com/vaadin/flow/webcomponent/ClientSelectExporter.java

@@ -19,11 +19,9 @@
 import com.vaadin.flow.component.WebComponentExporter;
 import com.vaadin.flow.component.page.AppShellConfigurator;
 import com.vaadin.flow.component.webcomponent.WebComponent;
-import com.vaadin.flow.router.Route;
 import com.vaadin.flow.server.PWA;
 
 @PWA(name = "Client select exporter", shortName = "Client select")
-@Route
 public class ClientSelectExporter
         extends WebComponentExporter<ClientSelectComponent>
         implements AppShellConfigurator {