[1546] Fix DnD from the diagram background to a Package node

CHANGELOG.adoc

@@ -59,6 +59,9 @@ As a consequence, the `syson-table-requirements-view` and `syson-common-view` mo
 `GetIntermediateContainerCreationSwitch.java` has been moved from `syson-application-configuration` to `syson-services`.
 - https://github.com/eclipse-syson/syson/issues/1245[#1245] [syson] Standardize read-only computation.
 The class `SysMLReadOnlyService` and the interface `ISysMLReadOnlyService` have been removed, use `IReadOnlyObjectPredicate` instead.
+- https://github.com/eclipse-syson/syson/issues/1546[#1546] [diagrams] Fix drag and drop of a graphical node from the diagram background into a _Package_ graphical node.
+As a consequence, the `ViewToolService#expose` method has been moved into `ToolService.java` and `NodeFinder.java` has been moved from `syson-diagram-common-view` to `syson-services`.
+
 
 === Dependency update
 
@@ -79,6 +82,7 @@ This issue was not visible in SysON but could appear in downstream applications
 Now it has been fixed in Sirius Web 2025.8.4, `SysONUpdateLibraryExecutor` has been deleted and `UpdateLibraryExecutor` is used again.
 - https://github.com/eclipse-syson/syson/issues/1522[#1522] [diagrams] To avoid edge blinking when refreshing the diagram, we need to set the properties `measured.height` and `measured.width` with the value of the node layout data when converting a custom node accordingly to the xyflow https://reactflow.dev/learn/advanced-use/ssr-ssg-configuration#node-dimensions[documentation].
 - https://github.com/eclipse-syson/syson/issues/1545[#1545] [diagrams] Add _interconnection_ compartment to `PartDefinition` nodes in the standard diagrams.
+- https://github.com/eclipse-syson/syson/issues/1546[#1546] [diagrams] Fix drag and drop of a graphical node from the diagram background into a _Package_ graphical node.
 
 === Improvements
 

backend/application/syson-application/src/test/java/org/eclipse/syson/application/controllers/diagrams/compartments/ActionTransitionUsagesTests.java

@@ -33,14 +33,14 @@
 import org.eclipse.syson.AbstractIntegrationTests;
 import org.eclipse.syson.application.controllers.diagrams.testers.ToolTester;
 import org.eclipse.syson.application.data.ActionTransitionUsagesProjectData;
-import org.eclipse.syson.diagram.common.view.services.NodeFinder;
 import org.eclipse.syson.services.diagrams.DiagramDescriptionIdProvider;
 import org.eclipse.syson.services.diagrams.api.IGivenDiagramDescription;
 import org.eclipse.syson.services.diagrams.api.IGivenDiagramReference;
 import org.eclipse.syson.services.diagrams.api.IGivenDiagramSubscription;
 import org.eclipse.syson.standard.diagrams.view.SDVDescriptionNameGenerator;
 import org.eclipse.syson.sysml.SysmlPackage;
 import org.eclipse.syson.util.IDescriptionNameGenerator;
+import org.eclipse.syson.util.NodeFinder;
 import org.eclipse.syson.util.SysONRepresentationDescriptionIdentifiers;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;

backend/application/syson-application/src/test/java/org/eclipse/syson/application/controllers/diagrams/general/view/GVDropFromDiagramTests.java

@@ -0,0 +1,158 @@
+/*******************************************************************************
+ * Copyright (c) 2025 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
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Obeo - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.syson.application.controllers.diagrams.general.view;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.eclipse.sirius.components.diagrams.tests.DiagramEventPayloadConsumer.assertRefreshedDiagramThat;
+
+import com.jayway.jsonpath.JsonPath;
+
+import java.time.Duration;
+import java.util.UUID;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Consumer;
+
+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.DropNodeInput;
+import org.eclipse.sirius.components.core.api.SuccessPayload;
+import org.eclipse.sirius.components.diagrams.tests.graphql.DropNodeMutationRunner;
+import org.eclipse.sirius.components.diagrams.tests.navigation.DiagramNavigator;
+import org.eclipse.sirius.web.tests.services.api.IGivenInitialServerState;
+import org.eclipse.syson.AbstractIntegrationTests;
+import org.eclipse.syson.application.data.GeneralViewWithTopNodesTestProjectData;
+import org.eclipse.syson.services.diagrams.api.IGivenDiagramSubscription;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.jdbc.Sql;
+import org.springframework.test.context.jdbc.SqlConfig;
+import org.springframework.transaction.annotation.Transactional;
+
+import reactor.core.publisher.Flux;
+import reactor.test.StepVerifier;
+
+/**
+ * Tests the drag and drop of nodes inside the General View diagram.
+ *
+ * @author arichard
+ */
+@Transactional
+@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
+public class GVDropFromDiagramTests extends AbstractIntegrationTests {
+
+    @Autowired
+    private IGivenInitialServerState givenInitialServerState;
+
+    @Autowired
+    private IGivenDiagramSubscription givenDiagramSubscription;
+
+    @Autowired
+    private DropNodeMutationRunner dropNodeMutationRunner;
+
+    private Flux<DiagramRefreshedEventPayload> givenSubscriptionToDiagram() {
+        var diagramEventInput = new DiagramEventInput(UUID.randomUUID(),
+                GeneralViewWithTopNodesTestProjectData.EDITING_CONTEXT_ID,
+                GeneralViewWithTopNodesTestProjectData.GraphicalIds.DIAGRAM_ID);
+        var flux = this.givenDiagramSubscription.subscribe(diagramEventInput);
+        return flux;
+    }
+
+    @BeforeEach
+    public void beforeEach() {
+        this.givenInitialServerState.initialize();
+    }
+
+    @DisplayName("Given a diagram with some nodes, when a node is dropped in another one, then the diagram is updated")
+    @Sql(scripts = { GeneralViewWithTopNodesTestProjectData.SCRIPT_PATH }, executionPhase = Sql.ExecutionPhase.BEFORE_TEST_METHOD,
+            config = @SqlConfig(transactionMode = SqlConfig.TransactionMode.ISOLATED))
+    @Sql(scripts = { "/scripts/cleanup.sql" }, executionPhase = Sql.ExecutionPhase.AFTER_TEST_METHOD, config = @SqlConfig(transactionMode = SqlConfig.TransactionMode.ISOLATED))
+    @Test
+    public void dropPartFromDiagramToPackageThenFromPackageToPart() {
+        var flux = this.givenSubscriptionToDiagram();
+
+        var diagramId = new AtomicReference<String>();
+        var packageNodeId = new AtomicReference<String>();
+        var partNodeId = new AtomicReference<String>();
+
+        Consumer<Object> initialDiagramContentConsumer = assertRefreshedDiagramThat(diagram -> {
+            diagramId.set(diagram.getId());
+
+            var packageNode = new DiagramNavigator(diagram).nodeWithLabel("Package").getNode();
+            packageNodeId.set(packageNode.getId());
+
+            var partNode = new DiagramNavigator(diagram).nodeWithLabel("\u00ABref part\u00BB\npart").getNode();
+            partNodeId.set(partNode.getId());
+
+            assertThat(packageNode.getChildNodes()).hasSize(0);
+        });
+
+        Runnable dropPartNodeFromDiagramToPackage = () -> {
+            var input = new DropNodeInput(
+                    UUID.randomUUID(),
+                    GeneralViewWithTopNodesTestProjectData.EDITING_CONTEXT_ID.toString(),
+                    diagramId.get(),
+                    partNodeId.get(),
+                    packageNodeId.get(),
+                    0,
+                    0);
+            var result = this.dropNodeMutationRunner.run(input);
+            String typename = JsonPath.read(result, "$.data.dropNode.__typename");
+            assertThat(typename).isEqualTo(SuccessPayload.class.getSimpleName());
+        };
+
+        Consumer<Object> updatedDiagramContentConsumerAfterFirstDrop = assertRefreshedDiagramThat(diagram -> {
+            var packageNode = new DiagramNavigator(diagram).nodeWithLabel("Package").getNode();
+
+            var partNode = new DiagramNavigator(diagram).nodeWithLabel("\u00ABref part\u00BB\npart").getNode();
+            partNodeId.set(partNode.getId());
+
+            assertThat(packageNode.getChildNodes()).hasSize(1);
+            assertThat(packageNode.getChildNodes().get(0)).isEqualTo(partNode);
+        });
+
+        Runnable dropPartNodeFromPackageToDiagram = () -> {
+            var input = new DropNodeInput(
+                    UUID.randomUUID(),
+                    GeneralViewWithTopNodesTestProjectData.EDITING_CONTEXT_ID.toString(),
+                    diagramId.get(),
+                    partNodeId.get(),
+                    diagramId.get(),
+                    0,
+                    0);
+            var result = this.dropNodeMutationRunner.run(input);
+            String typename = JsonPath.read(result, "$.data.dropNode.__typename");
+            assertThat(typename).isEqualTo(SuccessPayload.class.getSimpleName());
+        };
+
+        Consumer<Object> updatedDiagramContentConsumerAfterSecondDrop = assertRefreshedDiagramThat(diagram -> {
+            var packageNode = new DiagramNavigator(diagram).nodeWithLabel("Package").getNode();
+
+            var partNode = new DiagramNavigator(diagram).nodeWithLabel("\u00ABref part\u00BB\npart").getNode();
+
+            assertThat(packageNode.getChildNodes()).hasSize(0);
+            assertThat(partNode).isNotNull();
+        });
+
+        StepVerifier.create(flux)
+                .consumeNextWith(initialDiagramContentConsumer)
+                .then(dropPartNodeFromDiagramToPackage)
+                .consumeNextWith(updatedDiagramContentConsumerAfterFirstDrop)
+                .then(dropPartNodeFromPackageToDiagram)
+                .consumeNextWith(updatedDiagramContentConsumerAfterSecondDrop)
+                .thenCancel()
+                .verify(Duration.ofSeconds(10));
+    }
+}

backend/application/syson-application/src/test/java/org/eclipse/syson/services/diagrams/DiagramComparator.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2024 Obeo.
+ * Copyright (c) 2024, 2025 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
@@ -17,7 +17,7 @@
 import org.eclipse.sirius.components.diagrams.Diagram;
 import org.eclipse.sirius.components.diagrams.Edge;
 import org.eclipse.sirius.components.diagrams.Node;
-import org.eclipse.syson.diagram.common.view.services.NodeFinder;
+import org.eclipse.syson.util.NodeFinder;
 import org.springframework.stereotype.Service;
 
 /**