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
setOriginalResources(resources);
	}
	/*
	 * (non-Javadoc)
	 * 
	 * This implementation copies the resources.
	 * 
	 * @see org.eclipse.ui.ide.undo.AbstractWorkspaceOperation#doExecute(org.eclipse.core.runtime.IProgressMonitor,
	 *      org.eclipse.core.runtime.IAdaptable)
	 */
	protected void doExecute(IProgressMonitor monitor, IAdaptable uiInfo)
			throws CoreException {
		copy(monitor, uiInfo); 
	}
	/**
	 * Move or copy any known resources according to the destination parameters
	 * known by this operation. Store enough information to undo and redo the
	 * operation.
	 * 
	 * @param monitor
	 *            the progress monitor to use for the operation
	 * @param uiInfo
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not
	 *            <code>null</code>, it contains an adapter for the
	 *            org.eclipse.swt.widgets.Shell.class
	 * @throws CoreException
	 *             propagates any CoreExceptions thrown from the resources API
	 */