Enable drop operation in Label in workbench

Dropping a file onto the top of an image wasn't possible on a label
containing an imageView. The issue was previously fixed via
eclipse-platform/eclipse.platform.swt#649. However, in the workbench
image, dropping was yet to be configured.The issue is now resolved by
calling a DropTarget on the shell obtained from the active
IWorkbenchWindow.

Fixes :eclipse-platform/eclipse.platform.swt#649

Author: elsazac

bundles/org.eclipse.e4.ui.workbench.renderers.swt/src/org/eclipse/e4/ui/workbench/renderers/swt/StackRenderer.java

@@ -87,6 +87,8 @@
 import org.eclipse.swt.custom.CTabFolder2Listener;
 import org.eclipse.swt.custom.CTabFolderEvent;
 import org.eclipse.swt.custom.CTabItem;
+import org.eclipse.swt.dnd.DND;
+import org.eclipse.swt.dnd.DropTarget;
 import org.eclipse.swt.events.ControlEvent;
 import org.eclipse.swt.events.ControlListener;
 import org.eclipse.swt.events.MouseAdapter;
@@ -719,6 +721,9 @@ public Object createWidget(MUIElement element, Object parent) {
 		if (PartStackUtil.isEditorStack(element)) {
 			createOnboardingControls(tabFolder);
 			initializeOnboardingInformationInEditorStack(tabFolder);
+			Label dropLabel = new Label(tabFolder, SWT.NONE);
+			int drop = DND.DROP_COPY | DND.DROP_MOVE | DND.DROP_LINK;
+			new DropTarget(dropLabel, drop);
 		}
 		tabFolder.setMRUVisible(getMRUValue());
 

tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/workbench/renderers/swt/StackRendererTest.java

@@ -417,7 +417,7 @@ public void testOnboardingRenderedWithCorrectSizeForEditorStack() {
 		Composite uiContainer = (Composite) ((StackRenderer) partStack.getRenderer()).getUIContainer(partStack);
 		CTabFolder tabFolder = (CTabFolder) ((Composite) uiContainer.getChildren()[0]).getChildren()[0];
 		assertNotNull(tabFolder.getChildren());
-		assertEquals(3, tabFolder.getChildren().length);
+		assertEquals(4, tabFolder.getChildren().length);
 
 		Composite outerOnboardingComposite = (Composite) tabFolder.getChildren()[2];
 		Rectangle expected = new Rectangle(StackRenderer.ONBOARDING_SPACING, StackRenderer.ONBOARDING_TOP_SPACING,
@@ -526,7 +526,7 @@ public void testOnboardingIsHiddenWhenEditorOpened() {
 		Composite uiContainer = (Composite) ((StackRenderer) partStack.getRenderer()).getUIContainer(partStack);
 		CTabFolder tabFolder = (CTabFolder) ((Composite) uiContainer.getChildren()[0]).getChildren()[0];
 		assertNotNull(tabFolder.getChildren());
-		assertEquals(3, tabFolder.getChildren().length);
+		assertEquals(4, tabFolder.getChildren().length);
 
 		Composite outerOnboardingComposite = (Composite) tabFolder.getChildren()[2];
 		Rectangle expected = new Rectangle(StackRenderer.ONBOARDING_SPACING, StackRenderer.ONBOARDING_TOP_SPACING,