Metric names are case sensitive

[dyladan]

The specification states that metric names are case insensitive. If we see a metric which is the same except for name-case, they are the same metric stream and should be exported as a single stream with the first encountered name. Currently we treat them as separate streams.

What would the guidance be for SDKs like JS that already made a different choice? Should we coalesce on the new behavior as a bug fix and just accept that it is breaking, or should we flag this for 2.0?

edit: to be clear, we didn't make this choice consciously. we simply missed it while building the metric sdk

I see this as a bug fix.

First off, there shouldn't be any public interfaces or functions that change from this. Only the export behavior.

Specifically for the duplicate stream case: the duplicate instrument registration section already specifies that identical instruments need to aggregated into a single data stream:

Originally posted by @MrAlias in open-telemetry/opentelemetry-specification#3539 (comment)

[dyladan]

@legendecas do you have time to look into this?

[legendecas]

I agree that tagging this as a bug fix is reasonable.