SQL: ordering doesn't work properly for multiple groupings

[astefan]

For a multi GROUP BY statement, the order in which the sources are used in the composite aggregation is incorrect.

For example, for the query SELECT first_name AS n, gender AS g FROM test GROUP BY n, g ORDER BY g, n the generated composite aggregation has the order of its sources like the one from the GROUP BY definition, where in fact it should be the one from the ORDER BY statement:

                "sources": [
                    {
                        "1331": {
                            "terms": {
                                "field": "first_name.keyword",
                                "missing_bucket": true,
                                "order": "asc"
                            }
                        }
                    },
                    {
                        "1335": {
                            "terms": {
                                "field": "gender",
                                "missing_bucket": true,
                                "order": "asc"
                            }
                        }
                    }
                ]