AspectGenerator 0.0.3-preview

Aspect Generator

The Aspect Generator can help you easily create your own aspects.

[!WARNING] Interceptors are an experimental compiler feature planned to ship in .NET 8 (with support for C# only). The feature may be subject to breaking changes or removal in a future release.

Download and Install

Install nuget

> dotnet add package AspectGenerator

Modify your project file

<PropertyGroup>
    ...
    <LangVersion>preview</LangVersion>
    <InterceptorsPreviewNamespaces>$(InterceptorsPreviewNamespaces);AspectGenerator</InterceptorsPreviewNamespaces>
</PropertyGroup>

OpenTelemetry Aspect example

Create OpenTelemetryFactory and Metrics aspect:

using System;
using System.Diagnostics;

using OpenTelemetry;
using OpenTelemetry.Resources;
using OpenTelemetry.Trace;

namespace AspectGenerator
{
    /// <summary>
    /// Initializes OpenTelemetry.
    /// </summary>
    static class OpenTelemetryFactory
    {
        public static TracerProvider? Create()
        {
            return Sdk.CreateTracerProviderBuilder()
                .SetResourceBuilder(ResourceBuilder.CreateDefault().AddService("MySample"))
                .AddSource("Sample.Aspect")
                .AddConsoleExporter()
                .Build();
        }
    }

    /// <summary>
    /// Metrics aspect.
    /// </summary>
    [Aspect(
        // Specify the name of the method used in the 'using' statement
        // that returns an IDisposable object.
        OnUsing = nameof(OnUsing)
        )]
    [AttributeUsage(AttributeTargets.Method, Inherited = false, AllowMultiple = false)]
    sealed class MetricsAttribute : Attribute
    {
        static readonly ActivitySource _activitySource = new("Sample.Aspect");

        public static Activity? OnUsing(InterceptInfo info)
        {
            return _activitySource.StartActivity(info.MemberInfo.Name);
        }
    }
}

Use it:

using System;
using System.Threading;

using Aspects;

namespace OpenTelemetryAspect
{
    static class Program
    {
        static void Main()
        {
            using var _ = OpenTelemetryFactory.Create();

            Method1();
            Method2();
            Method1();
        }

        [Metrics]
        public static void Method1()
        {
            Thread.Sleep(100);
        }

        [Metrics]
        public static void Method2()
        {
            Thread.Sleep(200);
        }
    }
}

Application output:

Activity.TraceId:            d47417e726824c7b39055efb4685a9dd
Activity.SpanId:             12fbf29f5b622e13
Activity.TraceFlags:         Recorded
Activity.ActivitySourceName: Sample.Aspect
Activity.DisplayName:        Method1
Activity.Kind:               Internal
Activity.StartTime:          2023-11-22T00:50:15.9079068Z
Activity.Duration:           00:00:00.1016180
Resource associated with Activity:
    service.name: MySample
    service.instance.id: 86dbd377-c850-42a3-b878-be07de30faf1
    telemetry.sdk.name: opentelemetry
    telemetry.sdk.language: dotnet
    telemetry.sdk.version: 1.6.0

Activity.TraceId:            b90735bfb52cb0b52a504d02bc5ead2e
Activity.SpanId:             75109ef3af25a3e9
Activity.TraceFlags:         Recorded
Activity.ActivitySourceName: Sample.Aspect
Activity.DisplayName:        Method2
Activity.Kind:               Internal
Activity.StartTime:          2023-11-22T00:50:16.0360160Z
Activity.Duration:           00:00:00.2058166
Resource associated with Activity:
    service.name: MySample
    service.instance.id: 86dbd377-c850-42a3-b878-be07de30faf1
    telemetry.sdk.name: opentelemetry
    telemetry.sdk.language: dotnet
    telemetry.sdk.version: 1.6.0

Activity.TraceId:            e9653008f381b6330a8e538e02b7a61d
Activity.SpanId:             be3d7cd1d4376bd7
Activity.TraceFlags:         Recorded
Activity.ActivitySourceName: Sample.Aspect
Activity.DisplayName:        Method1
Activity.Kind:               Internal
Activity.StartTime:          2023-11-22T00:50:16.2517480Z
Activity.Duration:           00:00:00.1135186
Resource associated with Activity:
    service.name: MySample
    service.instance.id: 86dbd377-c850-42a3-b878-be07de30faf1
    telemetry.sdk.name: opentelemetry
    telemetry.sdk.language: dotnet
    telemetry.sdk.version: 1.6.0

Generated code:

// <auto-generated/>
#pragma warning disable
#nullable enable

using System;

using SR  = System.Reflection;
using SLE = System.Linq.Expressions;
using SCG = System.Collections.Generic;

namespace Aspects
{
    static partial class Interceptors
    {
        static SR.MethodInfo GetMethodInfo(SLE.Expression expr)
        {
            return expr switch
            {
                SLE.MethodCallExpression mc => mc.Method,
                _                           => throw new InvalidOperationException()
            };
        }

        static SR.MethodInfo MethodOf<T>(SLE.Expression<Func<T>> func) => GetMethodInfo(func.Body);
        static SR.MethodInfo MethodOf   (SLE.Expression<Action>  func) => GetMethodInfo(func.Body);

        static SR. MemberInfo                 Method1_Interceptor_MemberInfo        = MethodOf(() => OpenTelemetryAspect.Program.Method1());
        static SCG.Dictionary<string,object?> Method1_Interceptor_AspectArguments_0 = new ()
        {
        };
        //
        /// <summary>
        /// Intercepts OpenTelemetryAspect.Program.Method1().
        /// </summary>
        //
        // Intercepts Method1().
        [System.Runtime.CompilerServices.InterceptsLocation(@"P:\AspectGenerator\Examples\OpenTelemetryAspect\Program.cs", line: 14, character: 4)]
        //
        // Intercepts Method1().
        [System.Runtime.CompilerServices.InterceptsLocation(@"P:\AspectGenerator\Examples\OpenTelemetryAspect\Program.cs", line: 16, character: 4)]
        //
        [System.Runtime.CompilerServices.CompilerGenerated]
        //[System.Diagnostics.DebuggerStepThrough]
        public static void Method1_Interceptor()
        {
            // Aspects.MetricsAttribute
            //
            var __info__0 = new Aspects.InterceptInfo<Void>
            {
                MemberInfo      = Method1_Interceptor_MemberInfo,
                AspectType      = typeof(Aspects.MetricsAttribute),
                AspectArguments = Method1_Interceptor_AspectArguments_0,
            };

            using (Aspects.MetricsAttribute.OnUsing(__info__0))
            {
                OpenTelemetryAspect.Program.Method1();
            }
        }

        static SR. MemberInfo                 Method2_Interceptor_MemberInfo        = MethodOf(() => OpenTelemetryAspect.Program.Method2());
        static SCG.Dictionary<string,object?> Method2_Interceptor_AspectArguments_0 = new ()
        {
        };
        //
        /// <summary>
        /// Intercepts OpenTelemetryAspect.Program.Method2().
        /// </summary>
        //
        // Intercepts Method2().
        [System.Runtime.CompilerServices.InterceptsLocation(@"P:\AspectGenerator\Examples\OpenTelemetryAspect\Program.cs", line: 15, character: 4)]
        //
        [System.Runtime.CompilerServices.CompilerGenerated]
        //[System.Diagnostics.DebuggerStepThrough]
        public static void Method2_Interceptor()
        {
            // Aspects.MetricsAttribute
            //
            var __info__0 = new Aspects.InterceptInfo<Void>
            {
                MemberInfo      = Method2_Interceptor_MemberInfo,
                AspectType      = typeof(Aspects.MetricsAttribute),
                AspectArguments = Method2_Interceptor_AspectArguments_0,
            };

            using (Aspects.MetricsAttribute.OnUsing(__info__0))
            {
                OpenTelemetryAspect.Program.Method2();
            }
        }
    }
}

More advanced vertion of the Metrics aspect can also set activity status.

[Aspect(
    OnUsing   = nameof(OnUsing),
    OnFinally = nameof(OnFinally)
    )]
[AttributeUsage(AttributeTargets.Method, Inherited = false, AllowMultiple = false)]
sealed class MetricsAttribute : Attribute
{
    static readonly ActivitySource _activitySource = new("Sample.Aspect");

    public static Activity? OnUsing(InterceptInfo info)
    {
        var activity = _activitySource.StartActivity(info.MemberInfo.Name);

        info.Tag = activity;

        return activity;
    }

    public static void OnFinally(InterceptInfo info)
    {
        if (info is { Tag: Activity activity, Exception: var ex })
            activity.SetStatus(ex is null ? ActivityStatusCode.Ok : ActivityStatusCode.Error);
    }
}