Metrics are obsolete

[eddynaka]

Fixes #1370.

Changes

Please provide a brief description of the changes here.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1611 (200c56b) into master (d3edc47) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1611      +/-   ##
==========================================
- Coverage   80.61%   80.60%   -0.02%     
==========================================
  Files         242      242              
  Lines        6578     6578              
==========================================
- Hits         5303     5302       -1     
- Misses       1275     1276       +1     

Impacted Files	Coverage Δ
src/OpenTelemetry.Api/Metrics/LabelSet.cs	100.00% <ø> (ø)
src/OpenTelemetry.Api/Metrics/MeasureMetric.cs	25.00% <ø> (ø)
src/OpenTelemetry.Api/Metrics/MeterFactoryBase.cs	0.00% <ø> (ø)
src/OpenTelemetry.Api/Metrics/MeterProvider.cs	100.00% <ø> (ø)
...penTelemetry.Api/Metrics/NoopBoundCounterMetric.cs	0.00% <ø> (ø)
...penTelemetry.Api/Metrics/NoopBoundMeasureMetric.cs	0.00% <ø> (ø)
src/OpenTelemetry.Api/Metrics/NoopCounterMetric.cs	14.28% <ø> (ø)
...nTelemetry.Api/Metrics/NoopDoubleObserverMetric.cs	0.00% <ø> (ø)
...etry.Api/Metrics/NoopDoubleObserverMetricHandle.cs	0.00% <ø> (ø)
...enTelemetry.Api/Metrics/NoopInt64ObserverMetric.cs	0.00% <ø> (ø)
... and 19 more

[cijothomas]

Will open a new issue to move CS0618 nowarn to individual metric related files, not for whole project.

[cijothomas]

@Austin-Tan Can you work on this? (a separate PR)

[Austin-Tan]

Sure I'll get started right now. Would you recommend just Ctrl+F'ing the project for references to components in src/OpenTelemetry/Metrics, and appending #pragma warning disable cs0618 to the top?
And double checking my understanding - why don't we want compiler warnings? Aren't we intending to make it clear that Metrics are experimental?

[cijothomas]

Metrics are marked Obsolete so customers should be alerted. But there are pieces in this repo itself which depends on the metric, so they should be excluded from this warning.

(current its a project level warning exclusion, which will prevent us from catching any real issues, outside of metrics).

[cijothomas]

Okay to merge once we get 2 approvals.

[alanwest]

LGTM