Metrics should enforce labels by typing

[tomerghelber-tm]

Is your feature request related to a problem? Please describe.

Right now, when a label is required for a Metric, it is not enforced and potentially corrupted metrics can be sent.
We are testing the output of the metrics but the promotheus library is able to enforce that.
It also enables us to put some constants as labels and create a wrapped metric, which needs fewer labels.

Describe the solution you'd like

Please add to the metrics a generic place for the required labels.
If it is possible to add the "partial labeling of a metric" it would be great!

Describe alternatives you've considered

We are wrapping the creation and access of the built-in metric to enforce the labels in the types.

Additional context

Here is some code for example:

class MyCounter<MissingLabelName extends string> {
    constructor(
        private readonly labelNames: MissingLabelName[],
        private readonly labelValues: Record<Exclude<string, MissingLabelName>, string>
    ) {
    }

    labels<FilledLabelName extends MissingLabelName>(
        labelValues: Record<FilledLabelName, string>
    ): MyCounter<Exclude<MissingLabelName, FilledLabelName>> {
        type StillMissingLabelName = Exclude<MissingLabelName, FilledLabelName>
        function isNotFilled(labelName: MissingLabelName): labelName is StillMissingLabelName {
            return !(labelName in labelValues)
        }
        const labelNames: StillMissingLabelName[] = this.labelNames.filter(isNotFilled)
        const filledLabelValues = {
            ...this.labelValues,
            ...labelValues
        } as unknown as Record<Exclude<string, Exclude<MissingLabelName, FilledLabelName>>, string>
        return new MyCounter<Exclude<MissingLabelName, FilledLabelName>>(
            labelNames,
            filledLabelValues
        );
    }

    public inc(
        value: number=1,
        labelValues: Record<MissingLabelName, string>
    ): void {
        const allLabelValue = {
            ...this.labelValues,
            ...labelValues
        } as Record<string, string>
        console.log(`${JSON.stringify(allLabelValue)} ${value}`)
    }
}

const counter = new MyCounter(["version", "type"])
const partial = counter.labels({ version: "1.0" })
partial.inc(2, { type: "double_click" })
counter.inc(1, { version: "1.1", type: "click" })
// partial.inc(1) TYPE ERROR
// counter.inc(1, { type: "double_click" }) TYPE ERROR

[legendecas]

I think this is an interesting feature. I would suggest experimenting with the type interfaces in @opentelemetry/api-metrics and try not to put a requirement for SDKs to do anything to support it (i.e. enforcing the actual filters).

[dyladan]

I think this is an interesting feature. I would suggest experimenting with the type interfaces in @opentelemetry/api-metrics and try not to put a requirement for SDKs to do anything to support it (i.e. enforcing the actual filters).

If the required labels are known by the user creating the metric then maybe this can be accomplished with generics on create{metricType} methods.

[tomerghelber-tm]

Sorry, It was closed because I tried to merge in my fork