Telemetry SourceGenerator

Purview Telemetry Source Generator

Generates ActivitySource, ILogger, and Metrics based telemetry from methods you define on an interface.

Current Version: 5.0.0-prerelease.1

This approach allows for:

• Zero boilerplate - define methods on an interface, get full telemetry implementation generated
• Multi-target generation - generate Activities, Logging, and Metrics from a single interface
• Testable - easy mocking/substitution for unit testing (sample project)
• DI-ready - automatic dependency injection registration helpers
• OpenTelemetry-aligned - defaults to OpenTelemetry semantic conventions for better observability

Supported Frameworks

• .NET Framework 4.8 or higher
• .NET 8 or higher

Documentation

Getting Started

• Getting Started - Quick start guide with practical examples
• Sample Application - Full .NET Aspire demo application

Core Features

• Activities - Distributed tracing generation with ActivitySource
• Logging - Structured logging generation with ILogger
  • Generation v2 - Default mode with Microsoft.Extensions.Telemetry.Abstractions
  • Generation v1 - Legacy high-performance logging mode
• Metrics - Metrics generation (Counters, Histograms, Observables)
• Multi-Targeting - Combine Activities + Logging + Metrics in one interface

Configuration

• Generation Options - Control class names, DI, and code generation
• TagAttribute - Adding tags/properties to telemetry
• Generated Output - Examples of generated code

Reference

• FAQ - Frequently asked questions and troubleshooting
• Diagnostics - Analyzer warnings and errors
• Breaking Changes - Migration guide for v3 → v4 and earlier versions
• Performance - Full cross-runtime benchmark results

Contributing

• Contributing - Development setup, changeset workflow, and release process

Migration & Breaking Changes

Upgrading from v3? See the Breaking Changes guide for:

• Namespace Consolidation - All attributes now in Purview.Telemetry
• OpenTelemetry-Aligned Naming - New default naming conventions

All marker attributes are generated as conditional, meaning they will not be present in your build. However, you can define PURVIEW_TELEMETRY_ATTRIBUTES as a build constant to retain them. They are generated as internal to avoid exposing them outside of the assembly.

Reference in your .csproj or Directory.Build.props file:

<PackageReference Include="Purview.Telemetry.SourceGenerator" Version="5.0.0-prerelease.1">
  <PrivateAssets>all</PrivateAssets>
  <IncludeAssets>analyzers</IncludeAssets>
</PackageReference>

Basic Examples

The following examples all contain explicit definitions, meaning each example explicitly applies the appropriate attributes. Inferring certain actions or values is also supported and will be detailed in each sub-section.

The documentation for each generation target (activity, logging and metrics) contains information on what can be inferred.

By default each interface used as a source for generation includes an extension method for registering it with an IServiceCollection instance. More details can be found in Generation.

Tip

You can mix-and-match generation targets within a single interface, however the ability to infer is more limited. This is called multi-targeting.

Note

In .NET, Activities, Events, and Metrics refer to additional properties captured at creation, recording, or observation time as tags. However, in Open Telemetry these are referred to as attributes. As this source generator makes extensive use of marker attributes to control source code generation, we will use the term tags to describe these properties, and attributes as the .NET Attribute type not as the Open Telemetry definition.

An example project is available in the samples folder. Information can be found here.

Activities

Basic example of an activity-based telemetry interface.

There is one Activity (GettingItemFromCache) and four events. Calling these will add an ActivityEvent to the activity parameter. Alternatively, if no Activity is passed in, the Activity.Current will be used in it’s place.

There is also a ‘context’ method, that will add its properties as either tags or baggage to the current Activity.

The [Tag] and [Baggage] attributes on the parameters will add the values to the Activity or ActivityEvent.

[ActivitySource("some-activity")]
interface IActivityTelemetry
{
    [Activity]
    Activity? GettingItemFromCache([Baggage]string key, [Tag]string itemType);

    [Event("cachemiss")]
    void Miss(Activity? activity);

    [Event("cachehit")]
    void Hit(Activity? activity);

    [Event]
    void Error(Activity? activity, Exception ex);

    [Event]
    void Finished(Activity? activity, [Tag]TimeSpan duration);

    [Context]
    void AdditionalInfo(Activity? activity, string state);
}

More information can be found here.

Logging

Basic example of a structured logging-based interface.

Note

The ProcessingWorkItem method returns an IDisposable?, this is a scoped log entry.

All of the parameters are passed into the logger methods as properties.

[Logger]
interface ILoggingTelemetry
{
    [Log]
    IDisposable? ProcessingWorkItem(Guid id);

    [Log(LogLevel.Trace)]
    void ProcessingItemType(ItemTypes itemType);

    [Error]
    void FailedToProcessWorkItem(Exception ex);

    [Info]
    void ProcessingComplete(bool success, TimeSpan duration);
}

More information can be found here, including the different types of code generation, and how to disable logging generation when the Microsoft.Extensions.Logging types are unavailable.

Metrics

This example shows each meter type currently supported. Note the Counter attribute is demoed twice. Once with AutoIncrement set to true, this means the measurement value is automatically set to increment by 1 each time the method is called. In the other example (where AutoIncrement is false, which is the default) the measurement value is specified explicitly as a parameter using the InstrumentMeasurementAttribute.

Caution

Non-auto increment meters must specify a measurement with one of the valid types: byte, short, int, long, float, double, and decimal.

Note

Observable types must always have a System.Func<> with one of the following supported types:

• Any one of the following supported measurement types: byte, short, int, long, float, double, or decimal
• Measurement<T> where T is one of valid measurement types above.
• IEnumerable<Measurement<T>> where T is one of valid measurement types above.

As with activities, you can add a [Tag] to the parameters and they’ll be included at recording time for the instrument.

[Meter]
interface IMeterTelemetry
{
    [AutoCounter]
    void AutoIncrementMeter([Tag]string someValue);

    [Counter(AutoIncrement = true)]
    void AutoIncrementCounterMeter([Tag]string someValue);

    [Counter]
    void CounterMeter([InstrumentMeasurement]int measurement, [Tag]float someValue);

    [AutoCounter]
    void AutoCounterMeter([Tag]float someValue);

    [Histogram]
    void HistogramMeter([InstrumentMeasurement]int measurement, [Tag]int someValue, [Tag]bool anotherValue);

    [ObservableCounter]
    void ObservableCounterMeter(Func<float> measurement, [Tag]double someValue);

    [ObservableGauge]
    void ObservableGaugeMeter(Func<Measurement<float>> measurement, [Tag]double someValue);

    [ObservableUpDownCounter]
    void ObservableUpDownCounter(Func<IEnumerable<Measurement<byte>>> measurement, [Tag]double someValue);

    [UpDownCounter]
    void UpDownCounterMeter([InstrumentMeasurement]decimal measurement, [Tag]byte someValue);
}

More information can be found here.

Multi-Targeting

In this example, all method-based targets are explicitly set as inferring their usage is not support when using multi-targeting.

[ActivitySource("multi-targeting")]
[Logger]
[Meter]
interface IServiceTelemetry
{
    [Activity]
    [Trace]
    Activity? StartAnActivity(string tagStringParam, [Baggage]int entityId);

    [Event]
    [Info]
    void AnInterestingEvent(Activity? activity, float aTagValue);

    [Error]
    [Event]
    [AutoCounter]
    void AnError(Activity? activity, Exception ex);

    [Context]
    [AutoCounter]
    [Debug]
    void InterestingInfo(Activity? activity, float anotherTagValue, int intTagValue);

    [Histogram]
    [Trace]
    void ProcessingEntity(int entityId, string property1);

    [Info]
    [Counter]
    void ACounter([Tag]int value);
}

More information can be found here.