Expose TemporalitySelector funcs

[dprotaso]

This PR exposes the default TemporalitySelector funcs that are used by the OTel env var processing.

The reason to expose these funcs is because there is some discrepancy in various vendor documentation on how to enable these settings using go option args WithTemporalitySelector

https://cloud-native.slack.com/archives/C01NPAXACKT/p1757443233624599

[codecov]

Codecov Report

❌ Patch coverage is 34.42623% with 40 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.8%. Comparing base (0d5aa14) to head (49a4a6e).
⚠️ Report is 115 commits behind head on main.

Files with missing lines	Patch %	Lines
sdk/metric/temporality.go	0.0%	18 Missing ⚠️
sdk/metric/reader.go	20.0%	12 Missing ⚠️
...tlpmetric/otlpmetricgrpc/internal/oconf/options.go	0.0%	5 Missing ⚠️
...tlpmetric/otlpmetrichttp/internal/oconf/options.go	0.0%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #7346     +/-   ##
=======================================
- Coverage   82.9%   82.8%   -0.2%     
=======================================
  Files        267     268      +1     
  Lines      24982   24990      +8     
=======================================
- Hits       20729   20698     -31     
- Misses      3877    3916     +39     
  Partials     376     376             

Files with missing lines	Coverage Δ
...pmetric/otlpmetricgrpc/internal/oconf/envconfig.go	96.7% <100.0%> (-0.4%)	⬇️
...pmetric/otlpmetrichttp/internal/oconf/envconfig.go	96.7% <100.0%> (-0.4%)	⬇️
...tlpmetric/otlpmetricgrpc/internal/oconf/options.go	86.5% <0.0%> (-2.6%)	⬇️
...tlpmetric/otlpmetrichttp/internal/oconf/options.go	89.3% <0.0%> (-2.6%)	⬇️
sdk/metric/reader.go	68.4% <20.0%> (-31.6%)	⬇️
sdk/metric/temporality.go	0.0% <0.0%> (ø)

... and 2 files with indirect coverage changes

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[akats7]

@dprotaso question from the SIG, why not just expose the temporality selectors, what does the refactor/temporality preference type achieve

[dprotaso]

Hey @akats7

what does the refactor/temporality preference type achieve

Knative currently exposes a config map where users can set some OTel properties. Similar to how temporality preference can be configured using env vars we want our end-users to be able to use the same values supported by the otel-go SDK.

Having these functions/values exposed means we don't need to copy stuff from the SDK into our code base. I've highlighted in slack that this has lead to incorrect documentation from different vendors when they're telling users to write their own temporality selectors.

[dashpole]

I think we can expose the functions, but probably can't expose the string values. Those are only part of the OTLP exporter spec, not the SDK spec. See https://github.com/open-telemetry/opentelemetry-specification/blob/1e04e1be0e17cae6d01c862049bbeb298e0ffa06/specification/metrics/sdk_exporters/otlp.md?plain=1#L50

[dprotaso]

. Those are only part of the OTLP exporter spec, not the SDK spec

Does that mean the strings should be in a different package?

[dashpole]

Yeah, they probably belong in the otelconf package eventually.

[dprotaso]

What action should I take now then on this PR?

[dmathieu]

I would split this into two PRs. One that exposes the functions, the other that exposes the strings, so both can be discussed/merged separately.

[dprotaso]

I pulled the functions out into - #7434

[MrAlias]

These should not be added to the SDK. They duplicate existing configuration.

[dprotaso]

With the functions pulled out where should I put the functionality that maps the TemporalityPreference to *TemporalitySelector function?

[MrAlias]

With the functions pulled out where should I put the functionality that maps the TemporalityPreference to *TemporalitySelector function?

@dprotaso please see https://github.com/open-telemetry/opentelemetry-go/pull/7346/files#r2392819028

I do not plan to accept any additional overlapping configuration for temporarily in the SDK.

If you would like too support resolution of the selector functions, look at adding in otelconf as was mentioned.

[dashpole]

We discussed whether this even makes sense in otelconf, and we decided it probably does not. TemporalityPreference (the string constants) aren't part of the SDK spec. They are part of the declarative config spec for OTLP exporters, which would make the otelconf package a potential place for it to live, but we aren't ready right now to make subsections of the otelconf yaml parsing public right now. To start, we want to limit parsing to parsing the entire otelconf files.

[dprotaso]

@dashpole should I close this out and just creating a tracking issue or something?

[dashpole]

yeah. Please create the tracking issue in opentelemetry-go-contrib

[dprotaso]

done: open-telemetry/opentelemetry-go-contrib#8027