code: public void addClassNodeToCompile(ClassNode node, SourceUnit location) {
          String nodeName = node.getName();
          classesToCompile.put(nodeName, node);
          classNameToSource.put(nodeName, location);
      }
docs: this method actually does not compile a class. It's only
  a marker that this type has to be compiled by the CompilationUnit
  at the end of a parse step no node should be be left.