# Compute "per path" symbols.  For performance, we use the same ParseContext, which we
    # mutate (in a critical section) to set the rel_path appropriately before it's actually used.
    # This allows this memoized method to depend only on the symbol_table_cls, thus reusing
    # the same symbols for all parses.  Meanwhile we set the rel_path to None, so that we get
    # a loud error if anything tries to use it before it's set.
    # TODO: See <https://github.com/pantsbuild/pants/issues/3561>
    parse_context = ParseContext(rel_path=None, type_aliases=symbols)