BinModifier default value or null

[sunng87]

This might not be an issue at all, but to record different behaviour between our parser and prometheus default.

For this query statement, the output of prometheus 3.0 parse_query of process_virtual_memory_bytes / process_cpu_seconds_total is like:

{
	"data": {
		"bool": false,
		"lhs": {
			"matchers": [
				{
					"name": "__name__",
					"type": "=",
					"value": "process_virtual_memory_bytes"
				}
			],
			"name": "process_virtual_memory_bytes",
			"offset": 0,
			"startOrEnd": null,
			"timestamp": null,
			"type": "vectorSelector"
		},
		"matching": {
			"card": "one-to-one",
			"include": [],
			"labels": [],
			"on": false
		},
		"op": "/",
		"rhs": {
			"matchers": [
				{
					"name": "__name__",
					"type": "=",
					"value": "process_cpu_seconds_total"
				}
			],
			"name": "process_cpu_seconds_total",
			"offset": 0,
			"startOrEnd": null,
			"timestamp": null,
			"type": "vectorSelector"
		},
		"type": "binaryExpr"
	}
}

The matching part

		"matching": {
			"card": "one-to-one",
			"include": [],
			"labels": [],
			"on": false
		},

In our implementation, BinModifier is set to None in this case.

There is a case when matching is set to Null in prometheus: 1 / process_cpu_seconds_total

{
	"data": {
		"bool": false,
		"lhs": {
			"type": "numberLiteral",
			"val": "1"
		},
		"matching": null,
		"op": "/",
		"rhs": {
			"matchers": [
				{
					"name": "__name__",
					"type": "=",
					"value": "process_cpu_seconds_total"
				}
			],
			"name": "process_cpu_seconds_total",
			"offset": 0,
			"startOrEnd": null,
			"timestamp": null,
			"type": "vectorSelector"
		},
		"type": "binaryExpr"
	}
}

Conclusion

For binary expression, prometheus only set matching to null when one of the argument is literal, when both are vectorSelector, prometheus generates default matching: {"card": "one-to-one"}.

In our implementation, BinModifier is always set to null if no modifier provided.