public String getDocComment() {
        // Our doc comment is contained in a map in our toplevel,
        // indexed by our tree.  Find our enter environment, which gives
        // us our toplevel.  It also gives us a tree that contains our
        // tree:  walk it to find our tree.  This is painful.
        Env<AttrContext> enterEnv = getEnterEnv();
        if (enterEnv == null)
            return null;
        JCTree tree = TreeInfo.declarationFor(sym, enterEnv.tree);
        return enterEnv.toplevel.docComments.get(tree);
    }