Logs: Add LogRecordData

[CodeBlanch]

[Goal is to pare down the amount of changes on #3305]

• Adds struct LogRecordData which will be used in pooling scenarios, by the LogEmitter API, and (potentially) the "Events" API currently under discussion
• Makes everything on LogRecord settable to unblock users who want to scrub data or otherwise modify it in their pipelines

Public API Changes

namespace OpenTelemetry.Logs
{
    public sealed class LogRecord
    {
        public DateTime Timestamp
        {
            get;
+           set;
        }
        public ActivityTraceId TraceId
        {
            get;
+           set;
        }
        public ActivitySpanId SpanId
        {
            get;
+           set;
        }
        public ActivityTraceFlags TraceFlags
        {
            get;
+           set;
        }
        public string? TraceState
        {
            get;
+           set;
        }
        public string? CategoryName
        {
            get;
+           set;
        }
        public LogLevel LogLevel
        {
            get;
+           set;
        }
        public EventId EventId
        {
            get;
+           set;
        }
        public Exception? Exception
        {
            get;
+           set;
        }
    }
}

[reyang]

LGTM.

[codecov]

Codecov Report

Merging #3378 (0e48f44) into main (3c38200) will decrease coverage by 0.07%.
The diff coverage is 65.07%.

@@            Coverage Diff             @@
##             main    #3378      +/-   ##
==========================================
- Coverage   85.91%   85.83%   -0.08%     
==========================================
  Files         270      271       +1     
  Lines        9482     9523      +41     
==========================================
+ Hits         8146     8174      +28     
- Misses       1336     1349      +13     

Impacted Files	Coverage Δ
src/OpenTelemetry/Logs/LogRecord.cs	84.00% <64.51%> (-12.97%)	⬇️
src/OpenTelemetry/Logs/LogRecordData.cs	65.62% <65.62%> (ø)
...ZPages/Implementation/ZPagesExporterEventSource.cs	56.25% <0.00%> (-6.25%)	⬇️
...Telemetry/Internal/SelfDiagnosticsEventListener.cs	97.65% <0.00%> (+0.78%)	⬆️
...ter.ZPages/Implementation/ZPagesActivityTracker.cs	100.00% <0.00%> (+2.85%)	⬆️
...entation/ExportClient/OtlpGrpcTraceExportClient.cs	50.00% <0.00%> (+14.28%)	⬆️
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	59.09% <0.00%> (+22.72%)	⬆️

[TimothyMothra]

Can the ctor here use the static method SetActivityContext to avoid code duplication?

[CodeBlanch]

Good question! Sadly, no. This is a weird quick of structs. The compiler doesn't let you access this until the struct has been fully assigned. The reason to call the helper would be to do that assignment so it violates the rule.

        public LogRecordData(Activity? activity = null)
        {
            ref LogRecordData instance = ref this; // Error CS0188  The 'this' object cannot be used before all of its fields have been assigned

            SetActivityContext(ref instance, activity);
        }

[TimothyMothra]

i missed that this was a struct. thanks for the explanation!