VARIATION Swap
input: {
    "pipeline": [
        {
            "$set": {
                "a": {
                    "$const": 1
                },
                "b": {
                    "$const": 1
                }
            }
        },
        {
            "$set": {
                "a": "$b",
                "b": "$a"
            }
        },
        {
            "$match": {
                "a": 1,
                "b": 1
            }
        }
    ]
}
output: {
    "$set:0": {
        "scope:0": {
            "exhaustiveScope": "scope:-1",
            "fields": {
                "<missing>:0": {
                    "declaringScope": "scope:0",
                    "dependencies": []
                },
                "a:1": {
                    "declaringScope": "scope:0",
                    "dependencies": []
                },
                "b:2": {
                    "declaringScope": "scope:0",
                    "dependencies": []
                }
            }
        },
        "dependencies": []
    },
    "$set:1": {
        "scope:1": {
            "exhaustiveScope": "scope:-1",
            "fields": {
                "<missing>:3": {
                    "declaringScope": "scope:1",
                    "dependencies": []
                },
                "a:4": {
                    "declaringScope": "scope:1",
                    "dependencies": [
                        "b:2"
                    ]
                },
                "b:5": {
                    "declaringScope": "scope:1",
                    "dependencies": [
                        "a:1"
                    ]
                }
            }
        },
        "dependencies": [
            "a:1",
            "b:2"
        ]
    },
    "$match:2": {
        "scope:1": "scope:1",
        "dependencies": [
            "a:4",
            "b:5"
        ]
    }
}

