Wildcard indexes produce incomplete explain output due to key collision

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    • Type: Bug
    • Resolution: Unresolved
    • Priority: Minor - P4
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    • Affects Version/s: None
    • Component/s: None
    • Query Optimization
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      Running the following on the legacy mongo shell vs mongosh produces different outputs:

      db.a.drop()
db.a.createIndex({a:1, "b.$**":1, c: 1})
db.a.insertOne({})
db.a.explain().find({a:1, c: 1}).finish().queryPlanner.winningPlan.inputStage.indexBounds

      On mongosh:

      {
  a: [ '[1, 1]' ],
  '$_path': [ '[MinKey, MaxKey]' ],
  c: [ '[MinKey, MaxKey]' ]
}

      On the legacy mongo shell:

      {
        "a" : [
                "[1.0, 1.0]"
        ],
        "$_path" : [
                "[MinKey, MinKey]",
                "[\"\", {})"
        ],
        "c" : [
                "[MinKey, MaxKey]"
        ]
}

      Neither is actually correct. The object really contains two $_path keys, and the legacy shell shows the first occurance, while mongosh shows the second. This is confusing and misleading.

            Assignee:
            Unassigned
            Reporter:
            Kartal Kaan Bozdogan
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              Created:
              Updated: