Bug 6700 Code assist should not just beep
suggest to show a status message: Could not complete due to syntax errors. This is also better for accessability reasons.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitEditor.java
public void dispose() {
				uninstall(fDocument);
			}
			
			public void uninstall(IDocument document) {
				if (document == fDocument && document != null) {
					try {
						fDocument.removePositionUpdater(fPositionUpdater);
						fDocument.removePositionCategory(fCategory);			
					} catch (BadPositionCategoryException x) {
						
					}
					fDocument= null;
				}
			}
			
			public void manage(Position position) {
				try {
					fDocument.addPosition(fCategory, position);
				} catch (BadPositionCategoryException x) {
					
				} catch (BadLocationException x) {
					
				}
			}
			
			public void unmanage(Position position) {
				try {
					fDocument.removePosition(fCategory, position);