eclipse-syson · pcdavid · Mar 13, 2026
diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
@@ -101,6 +101,7 @@ Now the _end_ keyword is not displayed anymore in the label of these graphical n
 - https://github.com/eclipse-syson/syson/issues/2058[#2058] [diagrams] Fix error when importing SysML snippets referencing unknown units which could make the resulting model inconsistent
 - https://github.com/eclipse-syson/syson/issues/2053[#2053] [diagrams] Prevent incoming and outgoing graphical edges of a graphical `ForkNode` or `JoinNode` to point empty space.
 - https://github.com/eclipse-syson/syson/issues/2059[#2059] [diagrams] Fix an issue where the _Add existing elements_ tool was not working correctly on the _action flow_ compartment of `ActionUsage` graphical nodes.
+- https://github.com/eclipse-syson/syson/issues/2056[#2056] [diagams] Fix the user feedback when dropping an `Element` which is already exposed on a diagram.
 
 === Improvements
 

diff --git a/.../eclipse/syson/application/controllers/diagrams/general/view/GVDropFromExplorerTests.java b/.../eclipse/syson/application/controllers/diagrams/general/view/GVDropFromExplorerTests.java
@@ -20,6 +20,7 @@
 
 import java.time.Duration;
 import java.util.List;
+import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.UUID;
@@ -28,21 +29,27 @@
 
 import org.eclipse.sirius.components.collaborative.diagrams.dto.DiagramEventInput;
 import org.eclipse.sirius.components.collaborative.diagrams.dto.DiagramRefreshedEventPayload;
+import org.eclipse.sirius.components.collaborative.diagrams.dto.InvokeSingleClickOnDiagramElementToolInput;
+import org.eclipse.sirius.components.collaborative.diagrams.dto.InvokeSingleClickOnDiagramElementToolSuccessPayload;
 import org.eclipse.sirius.components.collaborative.dto.CreateChildInput;
 import org.eclipse.sirius.components.collaborative.dto.CreateChildSuccessPayload;
 import org.eclipse.sirius.components.core.api.IEditingContext;
+import org.eclipse.sirius.components.core.api.IFeedbackMessageService;
 import org.eclipse.sirius.components.core.api.IIdentityService;
 import org.eclipse.sirius.components.core.api.IObjectSearchService;
 import org.eclipse.sirius.components.diagrams.Diagram;
 import org.eclipse.sirius.components.diagrams.Node;
+import org.eclipse.sirius.components.diagrams.ViewModifier;
+import org.eclipse.sirius.components.diagrams.tests.graphql.InvokeSingleClickOnDiagramElementToolMutationRunner;
+import org.eclipse.sirius.components.diagrams.tests.graphql.PaletteQueryRunner;
+import org.eclipse.sirius.components.diagrams.tests.navigation.DiagramNavigator;
 import org.eclipse.sirius.components.graphql.tests.ExecuteEditingContextFunctionSuccessPayload;
 import org.eclipse.sirius.components.representations.MessageLevel;
 import org.eclipse.sirius.components.view.emf.diagram.IDiagramIdProvider;
 import org.eclipse.sirius.web.tests.graphql.CreateChildMutationRunner;
 import org.eclipse.sirius.web.tests.services.api.IGivenInitialServerState;
 import org.eclipse.syson.AbstractIntegrationTests;
 import org.eclipse.syson.GivenSysONServer;
-import org.eclipse.syson.SysONTestsProperties;
 import org.eclipse.syson.application.controllers.diagrams.checkers.CheckDiagramElementCount;
 import org.eclipse.syson.application.controllers.diagrams.checkers.CheckNodeOnDiagram;
 import org.eclipse.syson.application.controllers.diagrams.testers.DropFromExplorerTester;
@@ -79,7 +86,7 @@
  * @author gdaniel
  */
 @Transactional
-@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT, properties = { SysONTestsProperties.NO_DEFAULT_LIBRARIES_PROPERTY })
+@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
 public class GVDropFromExplorerTests extends AbstractIntegrationTests {
 
     @Autowired
@@ -112,8 +119,18 @@ public class GVDropFromExplorerTests extends AbstractIntegrationTests {
     @Autowired
     private CreateChildMutationRunner createChildMutationRunner;
 
+    @Autowired
+    private PaletteQueryRunner paletteQueryRunner;
+
+    @Autowired
+    private InvokeSingleClickOnDiagramElementToolMutationRunner invokeSingleClickOnDiagramElementToolMutationRunner;
+
+    @Autowired
+    private IFeedbackMessageService feedbackMessageService;
+
     private final IDescriptionNameGenerator descriptionNameGenerator = new SDVDescriptionNameGenerator();
 
+
     private Flux<DiagramRefreshedEventPayload> givenSubscriptionToDiagram() {
         var diagramEventInput = new DiagramEventInput(UUID.randomUUID(),
                 GeneralViewAddExistingElementsTestProjectData.EDITING_CONTEXT_ID,
@@ -358,7 +375,7 @@ public void dropFromExplorerTwiceShouldNotExposeElementTwice() {
             List<Object> messages = JsonPath.read(result.data(), "$.data.dropOnDiagram.messages[*]");
             assertThat(messages).as("We should receive at least one message when dropping an already visible element").hasSizeGreaterThanOrEqualTo(1);
             String messageBody = JsonPath.read(result.data(), "$.data.dropOnDiagram.messages[0].body");
-            assertThat(messageBody).isEqualTo("The element part1 is already visible in its parent General View");
+            assertThat(messageBody).isEqualTo("The element part1 is already visible in its parent Package 1");
             String messageLevel = JsonPath.read(result.data(), "$.data.dropOnDiagram.messages[0].level");
             assertThat(messageLevel).isEqualTo(MessageLevel.WARNING.toString());
         };
@@ -376,6 +393,128 @@ public void dropFromExplorerTwiceShouldNotExposeElementTwice() {
                 .verify(Duration.ofSeconds(10));
     }
 
+    @GivenSysONServer({ GeneralViewAddExistingElementsTestProjectData.SCRIPT_PATH })
+    @Test
+    @DisplayName("GIVEN a diagram WHEN dropping a semantic element from the explorer on various targets THEN the user gets the appropriate feedback message")
+    public void dropFromExplorerFeedback() {
+        AtomicReference<Diagram> diagram = new AtomicReference<>();
+        AtomicReference<String> packageNodeId = new AtomicReference<>();
+        AtomicReference<String> attributeNodeId = new AtomicReference<>();
+        AtomicReference<String> hideToolId = new AtomicReference<>();
+
+        String package1Id = GeneralViewAddExistingElementsTestProjectData.SemanticIds.PACKAGE1_ID;
+        String attributeDefinition1Id = GeneralViewAddExistingElementsTestProjectData.SemanticIds.ATTRIBUTE_DEFINITION_1_ID;
+
+        var flux = this.givenSubscriptionToDiagram();
+
+        Consumer<Object> initialDiagramContentConsumer = assertRefreshedDiagramThat(diagram::set);
+
+        Runnable dropPackageOnDiagramBackground = () -> this.dropFromExplorer(diagram, null, package1Id, Optional.empty());
+
+        Consumer<Object> diagramWithPackageNodeConsumer = assertRefreshedDiagramThat(newDiagram -> {
+            new CheckDiagramElementCount(this.diagramComparator).hasNewNodeCount(1).check(diagram.get(), newDiagram);
+            var packageNode = new DiagramNavigator(newDiagram).nodeWithTargetObjectId(package1Id).getNode();
+            assertThat(packageNode).isNotNull();
+            packageNodeId.set(packageNode.getId());
+            diagram.set(newDiagram);
+        });
+
+        Runnable dropAttributeOnPackage = () -> this.dropFromExplorer(diagram, packageNodeId.get(), attributeDefinition1Id, Optional.empty());
+
+        Consumer<Object> diagramWithAttributeNodeConsumer = assertRefreshedDiagramThat(newDiagram -> {
+            // 3 new nodes: AttributeDefinition container and its 2 compartments
+            new CheckDiagramElementCount(this.diagramComparator).hasNewNodeCount(3).check(diagram.get(), newDiagram);
+            var attributeNode = new DiagramNavigator(newDiagram).nodeWithTargetObjectId(attributeDefinition1Id).getNode();
+            assertThat(attributeNode).isNotNull().extracting(Node::getState).isEqualTo(ViewModifier.Normal);
+            attributeNodeId.set(attributeNode.getId());
+            diagram.set(newDiagram);
+        });
+
+        Runnable getHideTool = () -> hideToolId.set(this.getQuickToolIdByLabel(diagram.get().getId(), attributeNodeId.get(), "Hide"));
+
+        Runnable dropAttributeOnDiagram = () -> this.dropFromExplorer(diagram,
+                null, attributeDefinition1Id,
+                Optional.of("The element AttributeDefinition1 is already visible in its parent Package1"));
+
+        Consumer<Object> diagramNotChangeConsumer = assertRefreshedDiagramThat(newDiagram -> {
+            new CheckDiagramElementCount(this.diagramComparator).check(diagram.get(), newDiagram);
+            diagram.set(newDiagram);
+        });
+
+        Runnable hideAttributeNode = () -> {
+            var input = new InvokeSingleClickOnDiagramElementToolInput(UUID.randomUUID(), GeneralViewAddExistingElementsTestProjectData.EDITING_CONTEXT_ID, diagram.get().getId(),
+                    List.of(attributeNodeId.get()), hideToolId.get(), 0, 0, List.of());
+            var result = this.invokeSingleClickOnDiagramElementToolMutationRunner.run(input);
+            String typename = JsonPath.read(result.data(), "$.data.invokeSingleClickOnDiagramElementTool.__typename");
+            assertThat(typename).isEqualTo(InvokeSingleClickOnDiagramElementToolSuccessPayload.class.getSimpleName());
+        };
+
+        Consumer<Object> atributeNodeHiddenConsumer = assertRefreshedDiagramThat(newDiagram -> {
+            new CheckDiagramElementCount(this.diagramComparator).check(diagram.get(), newDiagram);
+            var attributeNode = new DiagramNavigator(newDiagram).nodeWithTargetObjectId(attributeDefinition1Id).getNode();
+            assertThat(attributeNode).isNotNull().extracting(Node::getState).isEqualTo(ViewModifier.Hidden);
+            diagram.set(newDiagram);
+        });
+
+        Runnable dropAttributeOnDiagramNoMessage = () -> this.dropFromExplorer(diagram, null, attributeDefinition1Id, Optional.empty());
+
+        Runnable dropAttributeOnPackageAgain = () -> this.dropFromExplorer(diagram, packageNodeId.get(), attributeDefinition1Id, Optional.empty());
+
+        Consumer<Object> diagramWithAttributeNodeRevealedConsumer = assertRefreshedDiagramThat(newDiagram -> {
+            new CheckDiagramElementCount(this.diagramComparator).check(diagram.get(), newDiagram);
+            var attributeNode = new DiagramNavigator(newDiagram).nodeWithTargetObjectId(GeneralViewAddExistingElementsTestProjectData.SemanticIds.ATTRIBUTE_DEFINITION_1_ID).getNode();
+            assertThat(attributeNode).isNotNull().extracting(Node::getState).isEqualTo(ViewModifier.Normal);
+        });
+
+        StepVerifier.create(flux)
+                .consumeNextWith(initialDiagramContentConsumer)
+                .then(dropPackageOnDiagramBackground)
+                .consumeNextWith(diagramWithPackageNodeConsumer)
+                .then(dropAttributeOnPackage)
+                .consumeNextWith(diagramWithAttributeNodeConsumer)
+                .then(getHideTool)
+                .then(dropAttributeOnDiagram)
+                .consumeNextWith(diagramNotChangeConsumer)
+                .then(hideAttributeNode)
+                .consumeNextWith(atributeNodeHiddenConsumer)
+                .then(dropAttributeOnDiagramNoMessage)
+                .consumeNextWith(diagramNotChangeConsumer)
+                .then(dropAttributeOnPackageAgain)
+                .consumeNextWith(diagramWithAttributeNodeRevealedConsumer)
+                .thenCancel()
+                .verify(Duration.ofSeconds(10_000));
+    }
+
+    private void dropFromExplorer(AtomicReference<Diagram> diagram, String targetId, String elementId, Optional<String> expectedWarning) {
+        // Workaround: clear the messages left by the previous tool's execution
+        this.feedbackMessageService.getFeedbackMessages().clear();
+        var result = this.dropFromExplorerTester.dropFromExplorer(GeneralViewAddExistingElementsTestProjectData.EDITING_CONTEXT_ID, diagram,
+                targetId, elementId);
+        List<Object> messages = JsonPath.read(result.data(), "$.data.dropOnDiagram.messages[*]");
+        if (expectedWarning.isPresent()) {
+            assertThat(messages).hasSize(1);
+            String messageBody = JsonPath.read(result.data(), "$.data.dropOnDiagram.messages[0].body");
+            assertThat(messageBody).isEqualTo(expectedWarning.get());
+            String messageLevel = JsonPath.read(result.data(), "$.data.dropOnDiagram.messages[0].level");
+            assertThat(messageLevel).isEqualTo(MessageLevel.WARNING.toString());
+        } else {
+            assertThat(messages).isEmpty();
+        }
+    }
+
+    private String getQuickToolIdByLabel(String diagramId, String nodeId, String toolName) {
+        Map<String, Object> variables = Map.of(
+                "editingContextId", GeneralViewAddExistingElementsTestProjectData.EDITING_CONTEXT_ID,
+                "representationId", diagramId,
+                "diagramElementIds", List.of(nodeId));
+        var result = this.paletteQueryRunner.run(variables);
+        List<String> labels = JsonPath.read(result.data(), "$.data.viewer.editingContext.representation.description.palette.quickAccessTools[*].label");
+        assertThat(labels).contains(toolName);
+        int toolIndex = labels.indexOf(toolName);
+        List<String> ids = JsonPath.read(result.data(), "$.data.viewer.editingContext.representation.description.palette.quickAccessTools[*].id");
+        return ids.get(toolIndex);
+    }
+
     @GivenSysONServer({ GeneralViewEmptyTestProjectData.SCRIPT_PATH })
     @Test
     public void dropLibraryPackageFromExplorerOnDiagram() {

diff --git a/...va/org/eclipse/syson/application/controllers/diagrams/testers/DropFromExplorerTester.java b/...va/org/eclipse/syson/application/controllers/diagrams/testers/DropFromExplorerTester.java
@@ -23,7 +23,6 @@
 import org.eclipse.sirius.components.collaborative.diagrams.dto.DropOnDiagramInput;
 import org.eclipse.sirius.components.collaborative.diagrams.dto.DropOnDiagramSuccessPayload;
 import org.eclipse.sirius.components.diagrams.Diagram;
-import org.eclipse.sirius.components.diagrams.tests.navigation.DiagramNavigator;
 import org.eclipse.sirius.components.graphql.tests.api.GraphQLResult;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Service;
@@ -54,12 +53,9 @@ public void dropFromExplorerOnDiagramElement(String projectId, AtomicReference<D
     }
 
     public GraphQLResult dropFromExplorer(String projectId, AtomicReference<Diagram> diagram, String targetNodeId, String semanticElementId) {
-        DiagramNavigator diagramNavigator = new DiagramNavigator(diagram.get());
-        final String targetId;
+        String targetId = targetNodeId;
         if (targetNodeId == null) {
             targetId = diagram.get().getId();
-        } else {
-            targetId = diagramNavigator.nodeWithId(targetNodeId).getNode().getId();
         }
         var dropOnDiagramInput = new DropOnDiagramInput(
                 UUID.randomUUID(),

diff --git a/...ava/org/eclipse/syson/application/data/GeneralViewAddExistingElementsTestProjectData.java b/...ava/org/eclipse/syson/application/data/GeneralViewAddExistingElementsTestProjectData.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2025 Obeo.
+ * Copyright (c) 2025, 2026 Obeo.
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v2.0
  * which accompanies this distribution, and is available at
@@ -39,6 +39,10 @@ public static final class SemanticIds {
 
         public static final String PACKAGE_1_ID = "8d4123ac-3ac5-412d-90f2-49282b923003";
 
+        public static final String PACKAGE1_ID = "98a777a3-15df-400f-a8d6-b5033e37e082";
+
+        public static final String ATTRIBUTE_DEFINITION_1_ID = "f42f0e49-8f00-49b4-b1ce-f4b0a98d3eb8";
+
         public static final String GENERAL_VIEW_VIEW_USAGE_ID = "b67872fa-5900-48d3-88f0-e6ced193c8ec";
 
         public static final String PART_1_ELEMENT_ID = "67a57df8-2995-41ea-a838-dfb3a9a8ee7f";