code: static PathFileObject createJarPathFileObject(JavacPathFileManager fileManager,
              final Path path) {
          return new PathFileObject(fileManager, path) {
              @Override
              String inferBinaryName(Iterable<? extends Path> paths) {
                  return toBinaryName(path);
              }
          };
      }
docs: Create a PathFileObject in a file system such as a jar file, such that
  the binary name can be inferred from its position within the filesystem.