Bug 162655 [Undo] [IDE] - Undoing a delete should check for existence of resources to be restored
N20061027. - I deleted two projects (along with their content). I read the warning that undo delete cannot restore the content and said "OK." - Then I checked out those same projects from HEAD. - Then I selected "Undo Delete Resources." This overwrote my code with empty projects. I think that "Undo Delete Resources" should become invalid if the resources exist again, because you'll end up replacing content without keeping a backup.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/ide/undo/CopyResourcesOperation.java
protected void copy(IProgressMonitor monitor, IAdaptable uiInfo)
			throws CoreException {
		monitor.beginTask("", 2000); 
		monitor
				.setTaskName(UndoMessages.AbstractResourcesOperation_CopyingResourcesProgress);
		List resourcesAtDestination = new ArrayList();
		List overwrittenResources = new ArrayList();
		for (int i = 0; i < resources.length; i++) {
			
			
			ResourceDescription[] overwrites;
			overwrites = WorkspaceUndoUtil.copy(
					new IResource[] { resources[i] }, getDestinationPath(
							resources[i], i), resourcesAtDestination,
					new SubProgressMonitor(monitor, 1000 / resources.length),
					uiInfo, true);
			
			for (int j = 0; j < overwrites.length; j++) {
				overwrittenResources.add(overwrites[j]);
			}
		}
		
		if (resourceDescriptions != null) {
			for (int i = 0; i < resourceDescriptions.length; i++) {
				if (resourceDescriptions[i] != null) {
					resourceDescriptions[i]
							.createResource(new SubProgressMonitor(monitor,
									1000 / resourceDescriptions.length));
				}
			}