[EXPORTER] prometheus: add otel_scope_name and otel_scope_version labels

[dashpole]

Part of #1841

Changes

From https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/compatibility/prometheus_and_openmetrics.md#instrumentation-scope-1:

Prometheus exporters MUST add the scope name as the otel_scope_name label and the scope version as the otel_scope_version label on all metric points by default, based on the scope the original data point was nested in.

This adds the otel_scope_name and otel_scope_version labels to all metrics, if they are non-empty.

[codecov]

Codecov Report

Merging #2293 (afa9009) into main (bd11434) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2293   +/-   ##
=======================================
  Coverage   87.39%   87.39%           
=======================================
  Files         199      199           
  Lines        6009     6009           
=======================================
  Hits         5251     5251           
  Misses        758      758           

[dashpole]

[ RUN      ] PrometheusExporterUtils.TranslateToPrometheusIntegerCounter
unknown file: Failure
C++ exception with description "basic_string::_M_create" thrown in the test body.

Any pointers on what this might be?

[dbolduc]

EDIT: I was wrong about this. There is an implicit conversion to std::string. I am not sure what will happen in the case where OTel uses the standard library though.

---

Also, maybe related, this part of the implementation is error prone:

opentelemetry-cpp/sdk/include/opentelemetry/sdk/instrumentationscope/instrumentation_scope.h

Line 140 in cdbc90a

: name_(name), version_(version), schema_url_(schema_url), attributes_(std::move(attributes))

This assumes that the string_views are null-terminated, which might not be the case. I can send a PR to fix it.

[dbolduc]

If you want to see the CI pass, you could steal the changes from #2301

opentelemetry-cpp/sdk/include/opentelemetry/sdk/metrics/export/metric_producer.h

Line 34 in 049f7e8

const opentelemetry::sdk::instrumentationscope::InstrumentationScope *scope_;

Basically make this

 const opentelemetry::sdk::instrumentationscope::InstrumentationScope *scope_ = nullptr;

[dbolduc]

I tried for an hour to get this to work. I am giving up. Here are some code nits for you:

[marcalff]

Please merge with a recent main, to resolve the conflicts.

[dashpole]

@marcalff done

[lalitb]

Depending on which PR is merged first - #2293 or #2301, the other PR will need to address merge conflicts. One argument could be to merge smaller and less complex PR (this?) first, so easy to resolve conflicts in other one.

[dashpole]

I'm happy to wait and rebase my PR.

[marcalff]

LGTM, thanks for the fix.