$merge corrupts field order in some cases on insert.

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    • Type: Bug
    • Resolution: Unresolved
    • Priority: Critical - P2
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    • Affects Version/s: 8.0.13
    • Component/s: None
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    • Query Execution
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      > db.foo.drop()

db.aggregate([{$documents:[{z: 1, a: 1}]}, {$merge: {into: "foo", whenMatched:"keepExisting", whenNotMatched:"insert"}}])

db.foo.find()

      When I run the above I get:

      [ { _id: ObjectId('68baf740fcc543022431a453'), a: 1, z: 1 } ]

      Note that `find` shows the `a` field first, even though the aggregation has `z` first.

      Per max.hirschhorn@mongodb.com, this bug is specific to this pair of whenMatched/whenNotMatched settings. It does not happen, for example, if `whenMatched` is `replace`.

      Workaround

      whenMatched: [{$replaceWith: "$$ROOT"}]

            Assignee:
            Unassigned
            Reporter:
            Felipe Gasper
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              Created:
              Updated: