Bug 40785 [plan item] Overview ruler improvements
- navigation from ruler to editor - hovering over header area shows number of errors/warning (header annotations in general)
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitDocumentProvider.java
IFileEditorInput input= (IFileEditorInput) element;
		ICompilationUnit original= createCompilationUnit(input.getFile());
		if (original != null) {
				
			try {
								
				try {
					refreshFile(input.getFile());
				} catch (CoreException x) {
					handleCoreException(x, JavaEditorMessages.getString("CompilationUnitDocumentProvider.error.createElementInfo")); 
				}
				
				IAnnotationModel m= createCompilationUnitAnnotationModel(input);
				IProblemRequestor r= m instanceof IProblemRequestor ? (IProblemRequestor) m : null;
				
				ICompilationUnit c= null;
				if (JavaPlugin.USE_WORKING_COPY_OWNERS)  {
					original.becomeWorkingCopy(r, getProgressMonitor());
					c= original;
				} else  {
					c= (ICompilationUnit) original.getSharedWorkingCopy(getProgressMonitor(), JavaPlugin.getDefault().getBufferFactory(), r);
				}
				
				DocumentAdapter a= null;
				try {
					a= (DocumentAdapter) c.getBuffer();
				} catch (ClassCastException x) {
					IStatus status= new Status(IStatus.ERROR, JavaUI.ID_PLUGIN, IJavaStatusConstants.TEMPLATE_IO_EXCEPTION, "Shared working copy has wrong buffer", x); 
					throw new CoreException(status);