private void addByFile(Env<AttrContext> env) {
        JavaFileObject file = env.toplevel.sourcefile;
        if (fileMap == null)
            fileMap = new HashMap<JavaFileObject, FileQueue>();
        FileQueue fq = fileMap.get(file);
        if (fq == null) {
            fq = new FileQueue();
            fileMap.put(file, fq);
            contentsByFile.add(fq);
        }
        fq.fileContents.add(env);
    }