# TODO(Eric Ayers) Extract this logic for general use? When using unpacked_jars it is needed
    # to get the correct source root for paths outside the current BUILD tree.
    for target in gentargets:
      for source in target.sources_relative_to_buildroot():
        src_root = self.context.source_roots.find_by_path(source)
        base = src_root.path if src_root else None
        if not base:
          base, _ = target.target_base, target.sources_relative_to_buildroot()
          self.context.log.debug('Could not find source root for {source}. Fell back to {base}.'
                                 .format(source=source, base=base))
        if base not in sources_by_base:
          sources_by_base[base] = OrderedSet()
        sources_by_base[base].add(source)
    return sources_by_base