code: def add_source_root(self, path, langs=tuple(), category=SourceRootCategories.UNKNOWN):
      
      self._trie.add_fixed(path, langs, category)
docs: Add the specified fixed source root, which must be relative to the buildroot.
  
      Useful in a limited set of circumstances, e.g., when unpacking sources from a jar with
      unknown structure.  Tests should prefer to use dirs that match our source root patterns
      instead of explicitly setting source roots here.