Add ghost elements to tool palette items through trigger actions

examples/org.eclipse.glsp.example.workflow/src/org/eclipse/glsp/example/workflow/handler/CreateWorkflowNodeOperationHandler.java

@@ -15,13 +15,15 @@
  ********************************************************************************/
 package org.eclipse.glsp.example.workflow.handler;
 
+import java.util.HashMap;
 import java.util.Optional;
 
 import org.eclipse.glsp.example.workflow.utils.ModelTypes;
 import org.eclipse.glsp.example.workflow.wfgraph.Category;
 import org.eclipse.glsp.graph.GCompartment;
 import org.eclipse.glsp.graph.GModelElement;
 import org.eclipse.glsp.graph.GPoint;
+import org.eclipse.glsp.server.actions.GhostElement;
 import org.eclipse.glsp.server.gmodel.GModelCreateNodeOperationHandler;
 import org.eclipse.glsp.server.operations.CreateNodeOperation;
 
@@ -50,4 +52,8 @@ protected Optional<GCompartment> getCategoryCompartment(final Category category)
          .filter(comp -> ModelTypes.STRUCTURE.equals(comp.getType())).findFirst();
    }
 
+   @Override
+   protected GhostElement createTriggerGhostElement(final String elementTypeId) {
+      return new GhostElement(createNode(Optional.empty(), new HashMap<>()), true);
+   }
 }

plugins/org.eclipse.glsp.server.emf/src/org/eclipse/glsp/server/emf/EMFCreateOperationHandler.java

@@ -16,8 +16,14 @@
 package org.eclipse.glsp.server.emf;
 
 import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.eclipse.glsp.server.actions.ActionDispatcher;
+import org.eclipse.glsp.server.actions.GhostElement;
+import org.eclipse.glsp.server.actions.TriggerElementCreationAction;
+import org.eclipse.glsp.server.actions.TriggerNodeCreationAction;
+import org.eclipse.glsp.server.operations.CreateNodeOperation;
 import org.eclipse.glsp.server.operations.CreateOperation;
 import org.eclipse.glsp.server.operations.CreateOperationHandler;
 
@@ -46,4 +52,27 @@ public EMFCreateOperationHandler(final List<String> handledElementTypeIds) {
    public void setHandledElementTypeIds(final List<String> handledElementTypeIds) {
       this.handledElementTypeIds = handledElementTypeIds;
    }
+
+   @Override
+   public List<TriggerElementCreationAction> getTriggerActions() {
+      if (CreateNodeOperation.class.isAssignableFrom(getHandledOperationType())) {
+         return getHandledElementTypeIds().stream().map(this::createTriggerNodeCreationAction)
+            .collect(Collectors.toList());
+      }
+      return CreateOperationHandler.super.getTriggerActions();
+   }
+
+   protected TriggerNodeCreationAction createTriggerNodeCreationAction(final String elementTypeId) {
+      return new TriggerNodeCreationAction(elementTypeId,
+         createTriggerArgs(elementTypeId),
+         createTriggerGhostElement(elementTypeId));
+   }
+
+   protected GhostElement createTriggerGhostElement(final String elementTypeId) {
+      return null;
+   }
+
+   protected Map<String, String> createTriggerArgs(final String elementTypeId) {
+      return null;
+   }
 }

plugins/org.eclipse.glsp.server/src/org/eclipse/glsp/server/actions/GhostElement.java

@@ -0,0 +1,63 @@
+/********************************************************************************
+ * Copyright (c) 2023 EclipseSource and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * https://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+package org.eclipse.glsp.server.actions;
+
+import java.util.Optional;
+
+import org.eclipse.glsp.graph.GModelElement;
+
+/**
+ * A ghost element describes an element that may be rendered as a schematic visualization of an element that may be
+ * inserted during creation.
+ */
+public class GhostElement {
+   private Object template;
+   private Boolean dynamic;
+
+   public GhostElement(final String templateElementId) {
+      this.template = templateElementId;
+   }
+
+   public GhostElement(final String templateElementId, final boolean dynamic) {
+      this.template = templateElementId;
+      this.dynamic = dynamic;
+   }
+
+   public GhostElement(final GModelElement element) {
+      this.template = element;
+   }
+
+   public GhostElement(final GModelElement element, final boolean dynamic) {
+      this.template = element;
+      this.dynamic = dynamic;
+   }
+
+   public Optional<String> getTemplateElementId() {
+      return template instanceof String templateElementId ? Optional.of(templateElementId) : Optional.empty();
+   }
+
+   public void setTemplateElementId(final String templateElementId) { this.template = templateElementId; }
+
+   public Optional<GModelElement> getTemplateElement() {
+      return template instanceof GModelElement templateElement ? Optional.of(templateElement) : Optional.empty();
+   }
+
+   public void setTemplateElement(final GModelElement templateElement) { this.template = templateElement; }
+
+   public Boolean getDynamic() { return dynamic; }
+
+   public void setDynamic(final boolean dynamic) { this.dynamic = dynamic; }
+}

plugins/org.eclipse.glsp.server/src/org/eclipse/glsp/server/actions/TriggerNodeCreationAction.java

@@ -25,6 +25,8 @@ public class TriggerNodeCreationAction extends TriggerElementCreationAction {
 
    public static final String KIND = "triggerNodeCreation";
 
+   private GhostElement ghostElement;
+
    public TriggerNodeCreationAction() {
       this(null);
    }
@@ -33,9 +35,23 @@ public TriggerNodeCreationAction(final String elementTypeId) {
       this(elementTypeId, new HashMap<>());
    }
 
+   public TriggerNodeCreationAction(final String elementTypeId, final GhostElement ghostElement) {
+      this(elementTypeId, new HashMap<>(), ghostElement);
+   }
+
    public TriggerNodeCreationAction(final String elementTypeId,
       final Map<String, String> args) {
       super(KIND, elementTypeId, args);
    }
 
+   public TriggerNodeCreationAction(final String elementTypeId,
+      final Map<String, String> args, final GhostElement ghostElement) {
+      super(KIND, elementTypeId, args);
+      this.ghostElement = ghostElement;
+   }
+
+   public GhostElement getGhostElement() { return ghostElement; }
+
+   public void setGhostElement(final GhostElement ghostElement) { this.ghostElement = ghostElement; }
+
 }

plugins/org.eclipse.glsp.server/src/org/eclipse/glsp/server/gmodel/GModelCreateNodeOperationHandler.java

@@ -18,13 +18,17 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.stream.Collectors;
 
 import org.eclipse.emf.common.command.Command;
 import org.eclipse.glsp.graph.GModelElement;
 import org.eclipse.glsp.graph.GNode;
 import org.eclipse.glsp.graph.GPoint;
 import org.eclipse.glsp.server.actions.ActionDispatcher;
+import org.eclipse.glsp.server.actions.GhostElement;
 import org.eclipse.glsp.server.actions.SelectAction;
+import org.eclipse.glsp.server.actions.TriggerElementCreationAction;
+import org.eclipse.glsp.server.actions.TriggerNodeCreationAction;
 import org.eclipse.glsp.server.operations.CreateEdgeOperation;
 import org.eclipse.glsp.server.operations.CreateNodeOperation;
 import org.eclipse.glsp.server.utils.LayoutUtil;
@@ -86,6 +90,26 @@ protected Optional<GModelElement> getContainer(final CreateNodeOperation operati
       return modelState.getIndex().get(operation.getContainerId());
    }
 
+   @Override
+   public List<TriggerElementCreationAction> getTriggerActions() {
+      return getHandledElementTypeIds().stream().map(this::createTriggerNodeCreationAction)
+         .collect(Collectors.toList());
+   }
+
+   protected TriggerNodeCreationAction createTriggerNodeCreationAction(final String elementTypeId) {
+      return new TriggerNodeCreationAction(elementTypeId,
+         createTriggerArgs(elementTypeId),
+         createTriggerGhostElement(elementTypeId));
+   }
+
+   protected GhostElement createTriggerGhostElement(final String elementTypeId) {
+      return null;
+   }
+
+   protected Map<String, String> createTriggerArgs(final String elementTypeId) {
+      return null;
+   }
+
    /**
     * Create and return the new Node at the specified (optional) location. The location
     * is given in coordinates relative to the