Add drag & drop support from Variables and Expressions to Debug Shell

Allow variables and expressions to be dragged from their respective
views and inserted into the Debug Shell at the caret location.

Author: SougandhS

org.eclipse.jdt.debug.ui/ui/org/eclipse/jdt/internal/debug/ui/display/DisplayView.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2021 IBM Corporation and others.
+ * Copyright (c) 2000, 2026 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -27,6 +27,10 @@
 import org.eclipse.core.commands.ExecutionException;
 import org.eclipse.core.commands.IHandler;
 import org.eclipse.core.commands.operations.IUndoContext;
+import org.eclipse.debug.core.DebugException;
+import org.eclipse.debug.core.model.IVariable;
+import org.eclipse.debug.core.model.IWatchExpression;
+import org.eclipse.debug.internal.ui.DebugUIPlugin;
 import org.eclipse.debug.ui.DebugUITools;
 import org.eclipse.debug.ui.IDebugUIConstants;
 import org.eclipse.jdt.debug.ui.IJavaDebugUIConstants;
@@ -62,14 +66,20 @@
 import org.eclipse.jface.text.IUndoManagerExtension;
 import org.eclipse.jface.text.source.ISourceViewer;
 import org.eclipse.jface.util.IPropertyChangeListener;
+import org.eclipse.jface.util.LocalSelectionTransfer;
 import org.eclipse.jface.util.PropertyChangeEvent;
+import org.eclipse.jface.viewers.ISelection;
 import org.eclipse.jface.viewers.ISelectionChangedListener;
+import org.eclipse.jface.viewers.IStructuredSelection;
 import org.eclipse.jface.viewers.SelectionChangedEvent;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.StyledText;
 import org.eclipse.swt.dnd.DND;
 import org.eclipse.swt.dnd.DragSource;
 import org.eclipse.swt.dnd.DragSourceAdapter;
+import org.eclipse.swt.dnd.DropTarget;
+import org.eclipse.swt.dnd.DropTargetAdapter;
+import org.eclipse.swt.dnd.DropTargetEvent;
 import org.eclipse.swt.dnd.TextTransfer;
 import org.eclipse.swt.dnd.Transfer;
 import org.eclipse.swt.widgets.Composite;
@@ -488,17 +498,87 @@ public void init(IViewSite site, IMemento memento) throws PartInitException {
      *
      * @since 3.4
      */
-    protected void initDragAndDrop() {
-        // Drag only
-    	DragSource ds = new DragSource(fSourceViewer.getTextWidget(), DND.DROP_COPY | DND.DROP_MOVE);
-    	ds.setTransfer(new Transfer[] {TextTransfer.getInstance()});
-    	ds.addDragListener(new DragSourceAdapter() {
-        	@Override
+	protected void initDragAndDrop() {
+		StyledText text = fSourceViewer.getTextWidget();
+		// Drag & Drop
+		DragSource ds = new DragSource(fSourceViewer.getTextWidget(), DND.DROP_COPY | DND.DROP_MOVE);
+		ds.setTransfer(new Transfer[] { TextTransfer.getInstance() });
+		ds.addDragListener(new DragSourceAdapter() {
+			@Override
 			public void dragSetData(org.eclipse.swt.dnd.DragSourceEvent event) {
-        		event.data = fSourceViewer.getTextWidget().getSelectionText();
-        	}
-        });
-    }
+				event.data = fSourceViewer.getTextWidget().getSelectionText();
+			}
+		});
+
+		DropTarget dropTarget = new DropTarget(text, DND.DROP_COPY | DND.DROP_MOVE);
+		dropTarget.setTransfer(new Transfer[] { LocalSelectionTransfer.getTransfer() });
+		dropTarget.addDropListener(new DropTargetAdapter() {
+
+			@Override
+			public void dragEnter(DropTargetEvent event) {
+				normalizeDrop(event);
+			}
+
+			@Override
+			public void dragOver(DropTargetEvent event) {
+				normalizeDrop(event);
+			}
+
+			@Override
+			public void drop(DropTargetEvent event) {
+				normalizeDrop(event);
+				String dropped = null;
+				if (TextTransfer.getInstance().isSupportedType(event.currentDataType)) {
+					dropped = (String) event.data;
+				}
+				if (dropped == null && LocalSelectionTransfer.getTransfer().isSupportedType(event.currentDataType)) {
+					ISelection selection = LocalSelectionTransfer.getTransfer().getSelection();
+
+					if (selection instanceof IStructuredSelection sel) {
+						List<Object> selections = sel.toList();
+						StringBuilder build = new StringBuilder();
+						for (Object obj : selections) {
+							if (obj instanceof IVariable var) {
+								try {
+									build.append(var.getName());
+								} catch (DebugException e) {
+									DebugUIPlugin.log(e);
+								}
+							} else if (obj instanceof IWatchExpression exp) {
+								build.append(exp.getExpressionText());
+							}
+							if (selections.size() > 1) {
+								build.append(System.lineSeparator());
+							}
+						}
+						dropped = build.toString();
+					}
+				}
+
+				if (dropped == null || dropped.isEmpty()) {
+					return;
+				}
+
+				StyledText text = fSourceViewer.getTextWidget();
+				int start = text.getSelection().x;
+				int len = text.getSelection().y - start;
+				text.replaceTextRange(start, len, dropped);
+				text.setCaretOffset(start + dropped.length());
+				text.setFocus();
+			}
+
+			private void normalizeDrop(DropTargetEvent event) {
+				if (event.detail == DND.DROP_NONE) {
+					event.detail = DND.DROP_COPY;
+				}
+
+				if (LocalSelectionTransfer.getTransfer().isSupportedType(event.currentDataType)) {
+					return;
+				}
+				event.detail = DND.DROP_NONE;
+			}
+		});
+	}
 
 	/**
 	 * Returns the entire trimmed contents of the current document.