> db.adminCommand({setParameter: 1, internalQueryFrameworkControl: "forceClassicEngine"});
> db.ds.insert({x: [{a: 1, b: 2}, {a: 2, b: 3}]});
> # $sort + $group w/ $first
> let pipeline1 = [{$sort: {"x.a": 1, "x.b": 1}}, {$group: {_id: "$x.a", o: {$first: "$x.b"}}}];
> # $group w/ $top is supposed to return the same result
> let pipeline2 = [{$group: {_id: "$x.a", o: {$top: {sortBy: {"x.a": 1, "x.b": 1}, output: "$x.b"}}}}];
> db.ds.aggregate(pipeline1);
{ "_id" : [ 1, 2 ], "o" : [ 2, 3 ] }
> db.ds.aggregate(pipeline2);
uncaught exception: Error: command failed: {
        "ok" : 0,
        "errmsg" : "PlanExecutor error during aggregation :: caused by :: cannot sort with keys that are parallel arrays",
        "code" : 2,
        "codeName" : "BadValue"
}