feat(sdk-metrics): added synchronous gauge to SDK

[clintonb]

Which problem is this PR solving?

Split from #4528, relates to #4296

Short description of the changes

Added SDK for synchronous gauge.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[clintonb]

FYI @pichlermarc

[clintonb]

@pichlermarc given the SDK depends on the API, is the order wrong here? It seems we should update the API first.

[pichlermarc]

@clintonb ah, this is the counter-intuitive situation I mentioned over at #4565. 🙂

Since @opentelemetry/sdk-metrics has a peer-dependency on @opentelemetry/api and that peer dependency allows for using API versions starting at 1.3.0, we can only use 1.3.0 types. Since Gauge will only be added in 1.9.0 we can't use it in this package (the current build failure simulates what would happen to a user when they have an older API - for instance 1.8.0 installed that does not have the Gauge type available).

The workaround is to copy the Gauge type from the API package to the @opentelemetry/sdk-metrics package. Since it's then copied 1:1 it'll be type-compatible with the API's version.

We're currently discussing ways to improve this situation with SDK 2.0 (many edge cases, difficult topic), but in the meantime this is the way forward to add the feature. 🙂

[pichlermarc]

One last comment, then I think this should be good to merge. 🙂
Thanks for working on this @clintonb 🚀

[codecov]

Codecov Report

Merging #4565 (512a359) into main (d66e1d7) will decrease coverage by 1.57%.
The diff coverage is 50.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4565      +/-   ##
==========================================
- Coverage   92.90%   91.33%   -1.57%     
==========================================
  Files         326      254      -72     
  Lines        9454     7112    -2342     
  Branches     2024     1614     -410     
==========================================
- Hits         8783     6496    -2287     
+ Misses        671      616      -55     

Files	Coverage Δ
...er-metrics-otlp-http/src/OTLPMetricExporterBase.ts	92.75% <50.00%> (-1.37%)	⬇️

... and 83 files with indirect coverage changes

[clintonb]

@pichlermarc I've rebased on main, added the @experimental comment flag, and updated the changelog.

Please take another look, and thanks for shepherding this!

[clintonb]

@pichlermarc this circular dependency continues to hamper my development. The sdk-metrics tests depend on api, so I cannot increase test coverage to meet the threshold for merging.

[clintonb]

See #4528 for complete test coverage.

[pichlermarc]

The sdk-metrics tests depend on api, so I cannot increase test coverage to meet the threshold for merging.

I see. I'll merge this without the needed coverage and then we follow up on it in the next PR. 👍

[clintonb]

@pichlermarc rebased both branches/PRs. Ready for tests and merging.