Nested $elemMatch query can uassert when multiple predicates are present

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    • Type: Bug
    • Resolution: Fixed
    • Priority: Major - P3
    • 8.3.0-rc0
    • Affects Version/s: 8.0.13, 8.3.0-rc0, 7.0.25-alpha0
    • Component/s: None
    • Query Optimization
    • Fully Compatible
    • ALL
    • v8.2, v8.0, v7.0
    • Hide 
      const coll = db.coll;
assert(coll.drop());
assert.commandWorked(coll.insert([{}]));

const q = [
    {
        "$addFields": {
            "a": 0,
        },
    },
    {
        "$match": {
            "a": {
                "$elemMatch": {
                    "$elemMatch": {
                        "$eq": 0,
                    },
                    "$in": [0],
                },
            },
        }
    },
    {
        "$project": {
            "_id": 0,
            "a": 1,
        },
    },
];

coll.aggregate(q).toArray();
// uassert: FieldPath cannot be constructed with empty string
      Show
      const coll = db.coll; assert (coll.drop()); assert .commandWorked(coll.insert([{}])); const q = [ { "$addFields" : { "a" : 0, }, }, { "$match" : { "a" : { "$elemMatch" : { "$elemMatch" : { "$eq" : 0, }, "$in" : [0], }, }, } }, { "$project" : { "_id" : 0, "a" : 1, }, }, ]; coll.aggregate(q).toArray(); // uassert: FieldPath cannot be constructed with empty string
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      Repro shows a valid query with nested $elemMatch hitting a uassert. It looks very similar to SERVER-101795, but at the time of filing that the issue was only reproducible on a time-series collection. This bug occurs on a regular collection.

      The uassert is hit during "createCanonicalQuery", so assigning it to Query Optimization for now.

            Assignee:
            Alya Berciu
            Reporter:
            Matt Boros
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              Created:
              Updated:
              Resolved: