[Exporter.Prometheus] Remove DisableTimestamp

[martincostello]

Fixes #7150

Changes

Removes the DisableTimestamp option from both OpenTelemetry.Exporter.Prometheus.AspNetCore and OpenTelemetry.Exporter.Prometheus.HttpListener.

As the Prometheus spec is MUST NOT and OpenMetrics is SHOULD NOT, I thought the cleanest option was complete removal, especially as these packages aren't stable yet anyway.

Alternative approaches could be:

1. Swap the default value to true.
2. Deprecate via [Obsolete] before removing.
3. Keep the property but document and implement it to only apply to OpenMetrics format.
4. 1, 2 & 3.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.00%. Comparing base (9b45df9) to head (e441126).
⚠️ Report is 3 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7176      +/-   ##
==========================================
- Coverage   89.08%   89.00%   -0.08%     
==========================================
  Files         271      271              
  Lines       13073    13043      -30     
==========================================
- Hits        11646    11609      -37     
- Misses       1427     1434       +7     

Flag	Coverage Δ
unittests-Project-Experimental	88.90% <100.00%> (-0.14%)	⬇️
unittests-Project-Stable	88.86% <100.00%> (-0.13%)	⬇️
unittests-UnstableCoreLibraries-Experimental	40.59% <100.00%> (-0.22%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ometheus.AspNetCore/PrometheusAspNetCoreOptions.cs	50.00% <ø> (-12.50%)	⬇️
...tpListener/Internal/PrometheusCollectionManager.cs	85.51% <100.00%> (-0.10%)	⬇️
...etheus.HttpListener/Internal/PrometheusExporter.cs	95.45% <ø> (-0.38%)	⬇️
...HttpListener/Internal/PrometheusExporterOptions.cs	100.00% <100.00%> (ø)
...heus.HttpListener/Internal/PrometheusSerializer.cs	87.05% <ø> (-0.72%)	⬇️
...s.HttpListener/Internal/PrometheusSerializerExt.cs	100.00% <100.00%> (ø)
...theusHttpListenerMeterProviderBuilderExtensions.cs	81.25% <ø> (-0.57%)	⬇️
...heus.HttpListener/PrometheusHttpListenerOptions.cs	100.00% <ø> (ø)

... and 1 file with indirect coverage changes

[Copilot]

Pull request overview

Removes the DisableTimestamp configuration surface from the Prometheus exporters and updates the shared serializer implementation to never emit explicit sample timestamps, aligning behavior with Prometheus/OpenMetrics guidance and the linked issue.

Changes:

• Removed DisableTimestamp from PrometheusAspNetCoreOptions and PrometheusHttpListenerOptions (plus associated internal plumbing).
• Updated the Prometheus serializer to stop writing timestamps and removed the now-unused timestamp writer helper.
• Updated unit/integration tests and benchmarks to reflect the new timestamp-less output.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusSerializerTests.cs	Updates serializer output assertions to no longer expect timestamps; removes disableTimestamp parameterization.
test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusHttpListenerTests.cs	Updates integration tests to stop configuring/expecting timestamps.
test/OpenTelemetry.Exporter.Prometheus.AspNetCore.Tests/PrometheusExporterMiddlewareTests.cs	Updates middleware integration tests to stop configuring/expecting timestamps (and removes timestamp parsing logic).
test/Benchmarks/Exporter/PrometheusSerializerBenchmarks.cs	Updates benchmark call site for the new serializer signature without disableTimestamp.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/PrometheusHttpListenerOptions.cs	Removes public DisableTimestamp option from HttpListener options.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/PrometheusHttpListenerMeterProviderBuilderExtensions.cs	Stops forwarding DisableTimestamp into exporter options.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializerExt.cs	Removes timestamp emission during metric point serialization and updates method signature.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusSerializer.cs	Removes WriteTimestamp helper since timestamps are no longer written.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusExporterOptions.cs	Removes DisableTimestamp and adjusts options initialization.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusExporter.cs	Removes internal DisableTimestamp state.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusCollectionManager.cs	Updates serializer invocation to new signature (no timestamp flag).
src/OpenTelemetry.Exporter.Prometheus.HttpListener/CHANGELOG.md	Notes breaking change for PrometheusHttpListenerOptions removal.
src/OpenTelemetry.Exporter.Prometheus.HttpListener/.publicApi/PublicAPI.Unshipped.txt	Removes unshipped API entries for DisableTimestamp on HttpListener options.
src/OpenTelemetry.Exporter.Prometheus.AspNetCore/PrometheusAspNetCoreOptions.cs	Removes public DisableTimestamp option from AspNetCore options.
src/OpenTelemetry.Exporter.Prometheus.AspNetCore/CHANGELOG.md	Notes breaking change for PrometheusAspNetCoreOptions removal.
src/OpenTelemetry.Exporter.Prometheus.AspNetCore/.publicApi/PublicAPI.Unshipped.txt	Removes unshipped API entries for DisableTimestamp on AspNetCore options.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[cijothomas]

Agree with this. (left non-blocking comments about unrelated changed)