Use latest metric description / help in Prometheus Exporter

[wjones127]

Component(s)

exporter/prometheus

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

If one changes the description of a metric, the Prometheus Exporter will ignore the change, and continue to emit metrics with the old help message. It will also emit a log message:

2025-06-03T18:54:40.508Z	info	prometheusexporter@v0.120.1/collector.go:453	Instrument description conflict, using existing	{"otelcol.component.id": "prometheus", "otelcol.component.kind": "Exporter", "otelcol.signal": "metrics", "instrument": "request_duration", "existing": "Duration of request in milliseconds", "dropped": "Duration of request in seconds"}

It looks like this was improved a while ago in #36356, where before the behavior was to just drop the metrics.

This seems to make it hard to update descriptions if they have typos or need additional information.

Describe the solution you'd like

It would be nice to choose the latest description, rather than the first in these instances. I'm assuming downstream consumers can handle this. If they can't, then we can disregard this.

Describe alternatives you've considered

The alternative is to create new metrics, and have people migrate to those.

Additional context

No response

[github-actions]

Pinging code owners:

• exporter/prometheus: @Aneurysm9 @dashpole @ArthurSens

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[dashpole]

Would the alternative be to restart collectors?

One of the things that is nice about the current approach is that the endpoint doesn't "flip flop" between different metadata. That can commonly happen if different clients are sending, or being scraped with conflicting descriptions, for example.

[wjones127]

Yeah, restarting collectors could be another solution. If that's the suggested solution, I think it might be worthwhile adding that to the warning messsage.

[dashpole]

That sgtm