code: public void addClassNodeToCompile(ClassNode node, SourceUnit location) {
          classesToCompile.put(node.getName(), node);
          classNameToSource.put(node.getName(), 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.