def _add_essential_scope_source(
        self, scope_source: Union[ScopeSource, List[ScopeSource]]
    ) -> None:
        """
        Add essential scope sources to functions.
        """
        for func in self.functions.values():
            func._add_essential_scope_source(scope_source)

        Add essential scope sources to functions.
        
coremltools/converters/mil/mil/program.py