Add source generated metrics doc

docs/core/diagnostics/metrics-generator.md

@@ -0,0 +1,92 @@
+---
+title: Compile-time metric source generation
+description: Learn how to use a source generator to create metrics in .NET
+ms.date: 04/11/2025
+---
+
+# Compile-time metric source generation
+
+.NET's metering infrastructure is designed to deliver a highly usable and high-performance metering solution for modern .NET applications.
+
+To use source-generated metering, create a class that defines the names and dimensions of the metrics your code can produce. Then, create the class with `partial` method signatures.
+
+The code generator automatically generates the code, which exposes strongly typed metering types and methods that you can invoke to record metric values. The generated methods are implemented in a highly efficient form, which reduces computation overhead as compared to traditional metering solutions.
+
+## Get started
+
+To get started, install the [📦 Microsoft.Extensions.Telemetry.Abstractions](https://www.nuget.org/packages/Microsoft.Extensions.Telemetry.Abstractions) NuGet package:
+
+### [.NET CLI](#tab/dotnet-cli)
+
+```dotnetcli
+dotnet add package Microsoft.Extensions.Telemetry.Abstractions
+```
+
+### [PackageReference](#tab/package-reference)
+
+```xml
+<ItemGroup>
+  <PackageReference Include="Microsoft.Extensions.Telemetry.Abstractions"
+                    Version="*" />
+</ItemGroup>
+```
+
+---
+
+For more information, see [dotnet add package](../tools/dotnet-package-add.md) or [Manage package dependencies in .NET applications](../tools/dependencies.md).
+
+## Generic attributes
+
+Generic attributes require C# 11 or later. For C# 10 or earlier, use nongeneric attributes instead.
+
+The following example shows a class that declares two metrics. The methods are marked with an attribute and are declared as `static` and `partial`.
+The code generator runs at build time and provides an implementation of these methods, along with accompanying
+types.
+
+:::code language="csharp" source="snippets/MetricsGen/MetricConstants.cs" id="snippet_metricConstants":::
+
+:::code language="csharp" source="snippets/MetricsGen/Metrics.cs" id="snippet_Metrics" :::
+
+The previous declaration automatically returns the following:
+
+- `Latency` class with a `Record` method
+- `TotalCount` class with an `Add` method
+- `TotalFailures` class with a `Add` method.
+
+The attributes indicate the set of dimensions that each metric uses. The signature for the generated types looks like this:
+
+```csharp
+internal class TotalCount
+{
+    public void Add(int value, object? env, object? region, object? requestName, object? requestStatus)
+}
+
+internal TotalFailures
+{
+    public void Add(int value)
+}
+
+internal class Latency
+{
+    public void Record(long value, object? requestName, object? duration);
+}
+```
+
+The dimensions specified in the attributes have been turned into arguments to the `Add` and `Record` methods. You then use the generated methods to create instances of these types. With the instances created, you can call `Add` and `Record` to register metric values, as shown in the following example:
+
+:::code language="csharp" source="snippets/MetricsGen/MyClass.cs" id ="snippet_metricCreation":::
+
+## Metric methods requirements
+
+Metric methods are constrained to the following:
+
+- They must be `public static partial`.
+- The return type must be unique.
+- Their names must not start with an underscore.
+- Their parameter names must not start with an underscore.
+- Their first parameter must be <xref:System.Diagnostics.Metrics.Meter> type.
+Metric methods are constrained to the following:
+
+## See also
+
+For more information on the supported metrics, see [Types of instruments](metrics-instrumentation.md#types-of-instruments) to learn how to choose which instrument to use in different situations.

docs/core/diagnostics/metrics-strongly-typed.md

@@ -11,95 +11,53 @@ Modern .NET applications can capture metrics using the <xref:System.Diagnostics.
 > [!NOTE]
 > In the context of metrics, a tag is sometimes also called a "dimension." This article uses "tag" for clarity and consistency with .NET metrics terminology.
 
-## Tag name defaults and customization
+## Get started
 
-By default, the source generator derives metric tag names from the field and property names of your tag class. In other words, each public field or property in the strongly-typed tag object becomes a tag name by default. You can override this by using the <xref:Microsoft.Extensions.Diagnostics.Metrics.TagNameAttribute> on a field or property to specify a custom tag name. In the examples below, you’ll see both approaches in action.
+To get started, install the [📦 Microsoft.Extensions.Telemetry.Abstractions](https://www.nuget.org/packages/Microsoft.Extensions.Telemetry.Abstractions) NuGet package:
 
-## Example 1: Basic metric with a single tag
+### [.NET CLI](#tab/dotnet-cli)
 
-The following example demonstrates a simple counter metric with one tag. In this scenario, we want to count the number of processed requests and categorize them by a `Region` tag:
-
-```csharp
-public struct RequestTags
-{
-    public string Region { get; set; }
-}
-
-public static partial class MyMetrics
-{
-    [Counter<int>(typeof(RequestTags))]
-    public static partial RequestCount CreateRequestCount(Meter meter);
-}
+```dotnetcli
+dotnet add package Microsoft.Extensions.Telemetry.Abstractions
 ```
 
-In the code above, `RequestTags` is a strongly-typed tag struct with a single property `Region`. The `CreateRequestCount` method is marked with <xref:Microsoft.Extensions.Diagnostics.Metrics.CounterAttribute`1> where `T` is an `int`, indicating it generates a **Counter** instrument that tracks `int` values. The attribute references `typeof(RequestTags)`, meaning the counter will use the tags defined in `RequestTags` when recording metrics. The source generator will produce a strongly-typed instrument class (named `RequestCount`) with an `Add` method that accepts integer value and `RequestTags` object.
+### [PackageReference](#tab/package-reference)
 
-To use the generated metric, create a <xref:System.Diagnostics.Metrics.Meter> and record measurements as shown below:
-
-```csharp
-Meter meter = new Meter("MyCompany.MyApp", "1.0");
-RequestCount requestCountMetric = MyMetrics.CreateRequestCount(meter);
-
-// Create a tag object with the relevant tag value
-var tags = new RequestTags { Region = "NorthAmerica" };
-
-// Record a metric value with the associated tag
-requestCountMetric.Add(1, tags);
+```xml
+<ItemGroup>
+  <PackageReference Include="Microsoft.Extensions.Telemetry.Abstractions"
+                    Version="*" />
+</ItemGroup>
 ```
 
-In this usage example, calling `MyMetrics.CreateRequestCount(meter)` creates a counter instrument (via the `Meter`) and returns a `RequestCount` metric object. When you call `requestCountMetric.Add(1, tags)`, the metric system records a count of 1 associated with the tag `Region="NorthAmerica"`. You can reuse the `RequestTags` object or create new ones to record counts for different regions, and the tag name `Region` will consistently be applied to every measurement.
+---
 
-## Example 2: Metric with nested tag objects
+For more information, see [dotnet add package](../tools/dotnet-package-add.md) or [Manage package dependencies in .NET applications](../tools/dependencies.md).
 
-For more complex scenarios, you can define tag classes that include multiple tags, nested objects, or even inherited properties. This allows a group of related metrics to share a common set of tags easily. In the next example, we define a set of tag classes and use them for three different metrics:
+## Tag name defaults and customization
 
-```csharp
-public class MetricTags : MetricParentTags
-{
-    [TagName("Dim1DimensionName")]
-    public string? Dim1;                      // custom tag name via attribute
+By default, the source generator derives metric tag names from the field and property names of your tag class. In other words, each public field or property in the strongly-typed tag object becomes a tag name by default. You can override this by using the <xref:Microsoft.Extensions.Diagnostics.Metrics.TagNameAttribute> on a field or property to specify a custom tag name. In the examples below, you’ll see both approaches in action.
 
-    public Operations Operation { get; set; } // tag name defaults to "Operation"
+## Example 1: Basic metric with a single tag
 
-    public MetricChildTags? ChildTagsObject { get; set; }
-}
+The following example demonstrates a simple counter metric with one tag. In this scenario, we want to count the number of processed requests and categorize them by a `Region` tag:
 
-public enum Operations
-{
-    Unknown = 0,
-    Operation1 = 1,
-}
+:::code language="csharp" source="snippets/MetricsGen/MyMetrics.cs" id= "snippet_SimpleMetricTag":::
 
-public class MetricParentTags
-{
-    [TagName("DimensionNameOfParentOperation")]
-    public string? ParentOperationName { get; set; }  // custom tag name via attribute
+In the code above, `RequestTags` is a strongly-typed tag struct with a single property `Region`. The `CreateRequestCount` method is marked with <xref:Microsoft.Extensions.Diagnostics.Metrics.CounterAttribute`1> where `T` is an `int`, indicating it generates a **Counter** instrument that tracks `int` values. The attribute references `typeof(RequestTags)`, meaning the counter will use the tags defined in `RequestTags` when recording metrics. The source generator will produce a strongly-typed instrument class (named `RequestCount`) with an `Add` method that accepts integer value and `RequestTags` object.
 
-    public MetricTagsStruct ChildTagsStruct { get; set; }
-}
+To use the generated metric, create a <xref:System.Diagnostics.Metrics.Meter> and record measurements as shown below:
 
-public class MetricChildTags
-{
-    public string? Dim2 { get; set; }  // tag name defaults to "Dim2"
-}
+:::code language="csharp" source="snippets/MetricsGen/MyClass.cs" id ="snippet_SimpleMetricTagUsage":::
 
-public struct MetricTagsStruct
-{
-    public string Dim3 { get; set; }   // tag name defaults to "Dim3"
-}
+In this usage example, calling `MyMetrics.CreateRequestCount(meter)` creates a counter instrument (via the `Meter`) and returns a `RequestCount` metric object. When you call `requestCountMetric.Add(1, tags)`, the metric system records a count of 1 associated with the tag `Region="NorthAmerica"`. You can reuse the `RequestTags` object or create new ones to record counts for different regions, and the tag name `Region` will consistently be applied to every measurement.
 
-public static partial class Metric
-{
-    [Histogram<long>(typeof(MetricTags))]
-    public static partial Latency CreateLatency(Meter meter);
+## Example 2: Metric with nested tag objects
 
-    [Counter<long>(typeof(MetricTags))]
-    public static partial TotalCount CreateTotalCount(Meter meter);
+For more complex scenarios, you can define tag classes that include multiple tags, nested objects, or even inherited properties. This allows a group of related metrics to share a common set of tags easily. In the next example, we define a set of tag classes and use them for three different metrics:
 
-    [Counter<int>(typeof(MetricTags))]
-    public static partial TotalFailures CreateTotalFailures(Meter meter);
-}
-```
+:::code language="csharp" source="snippets/MetricsGen/MetricTags.cs" :::
+:::code language="csharp" source="snippets/MetricsGen/Metrics.cs" id="snippet_MetricTags" :::
 
 In this example, `MetricTags` is a tag class that inherits from `MetricParentTags` and also contains a nested tag object (`MetricChildTags`) and a nested struct (`MetricTagsStruct`). The tag properties demonstrate both default and customized tag names:
 
@@ -113,55 +71,7 @@ All three metric definitions `CreateLatency`, `CreateTotalCount`, and `CreateTot
 
 The following code shows how to create and use these metrics in a class:
 
-```csharp
-internal class MyClass
-{
-    private readonly Latency _latencyMetric;
-    private readonly TotalCount _totalCountMetric;
-    private readonly TotalFailures _totalFailuresMetric;
-
-    public MyClass(Meter meter)
-    {
-        // Create metric instances using the source-generated factory methods
-        _latencyMetric = Metric.CreateLatency(meter);
-        _totalCountMetric = Metric.CreateTotalCount(meter);
-        _totalFailuresMetric = Metric.CreateTotalFailures(meter);
-    }
-
-    public void DoWork()
-    {
-        var stopwatch = new Stopwatch();
-        stopwatch.Start();
-        bool requestSuccessful = true;
-        // ... perform some operation ...
-        stopwatch.Stop();
-
-        // Create a tag object with values for all tags
-        var tags = new MetricTags
-        {
-            Dim1 = "Dim1Value",
-            Operation = Operations.Operation1,
-            ParentOperationName = "ParentOpValue",
-            ChildTagsObject = new MetricChildTags
-            {
-                Dim2 = "Dim2Value",
-            },
-            ChildTagsStruct = new MetricTagsStruct
-            {
-                Dim3 = "Dim3Value"
-            }
-        };
-
-        // Record the metric values with the associated tags
-        _latencyMetric.Record(stopwatch.ElapsedMilliseconds, tags);
-        _totalCountMetric.Add(1, tags);
-        if (!requestSuccessful)
-        {
-            _totalFailuresMetric.Add(1, tags);
-        }
-    }
-}
-```
+:::code language="csharp" source="snippets/MetricsGen/MyClass.cs" id ="snippet_strongMetricCreation":::
 
 In the preceding `MyClass.DoWork` method, a `MetricTags` object is populated with values for each tag. This single `tags` object is then passed to all three instruments when recording data. The `Latency` metric (a histogram) records the elapsed time, and both counters (`TotalCount` and `TotalFailures`) record occurrence counts. Because all metrics share the same tag object type, the tags (`Dim1DimensionName`, `Operation`, `Dim2`, `Dim3`, `DimensionNameOfParentOperation`) are present on every measurement.
 
@@ -184,6 +94,7 @@ Adhering to these requirements ensures that the source generator can successfull
 
 ## See also
 
+- [Source generated metrics in .NET](metrics-generator.md)
 - [Creating metrics in .NET (Instrumentation tutorial)](metrics-instrumentation.md)
 - [Collecting metrics in .NET (Using MeterListener and exporters)](metrics-collection.md)
 - [Logging source generation in .NET](../extensions/logger-message-generator.md) (for a similar source-generation approach applied to logging)

docs/core/diagnostics/metrics.md

@@ -28,6 +28,7 @@ There are two parts to using metrics in a .NET app:
 
 - [Instrumentation tutorial](metrics-instrumentation.md) - How to create new metrics in code
 - [Collection tutorial](metrics-collection.md) - How to store and view metric data for your app
+- [Source generated metrics](metrics-generator.md) - How to use source generator to create metrics
 - [Source-generated metrics with strongly-typed tags](metrics-strongly-typed.md) - How to use source-generated metrics with strongly-typed tags
 - [Built-in metrics](built-in-metrics.md) - Discover metrics that are ready for use in .NET runtime libraries
 - [Compare metric APIs](compare-metric-apis.md)

docs/core/diagnostics/snippets/MetricsGen/MetricConstants.cs

@@ -0,0 +1,12 @@
+namespace MetricsGen;
+
+//<snippet_metricConstants>
+internal class MetricConstants
+{
+    public const string EnvironmentName = "env";
+    public const string Region = "region";
+    public const string RequestName = "requestName";
+    public const string RequestStatus = "requestStatus";
+}
+// </snippet_metricConstants>
+

docs/core/diagnostics/snippets/MetricsGen/MetricTags.cs

@@ -0,0 +1,33 @@
+using Microsoft.Extensions.Diagnostics.Metrics;
+
+namespace MetricsGen;
+public class MetricTags : MetricParentTags
+{
+    [TagName("Dim1DimensionName")]
+    public string? Dim1;                      // custom tag name via attribute
+    public Operations Operation { get; set; } // tag name defaults to "Operation"
+    public MetricChildTags? ChildTagsObject { get; set; }
+}
+
+public enum Operations
+{
+    Unknown = 0,
+    Operation1 = 1,
+}
+
+public class MetricParentTags
+{
+    [TagName("DimensionNameOfParentOperation")]
+    public string? ParentOperationName { get; set; }  // custom tag name via attribute
+    public MetricTagsStruct ChildTagsStruct { get; set; }
+}
+
+public class MetricChildTags
+{
+    public string? Dim2 { get; set; }  // tag name defaults to "Dim2"
+}
+
+public struct MetricTagsStruct
+{
+    public string Dim3 { get; set; }   // tag name defaults to "Dim3"
+}

docs/core/diagnostics/snippets/MetricsGen/Metrics.cs

@@ -0,0 +1,43 @@
+#define FIRST // FIRST SECOND
+
+#if FIRST
+//<snippet_Metrics>
+using System.Diagnostics.Metrics;
+using Microsoft.Extensions.Diagnostics.Metrics;
+
+namespace MetricsGen;
+
+internal static partial class Metric
+{
+    // an explicit metric name is given
+    [Histogram<long>("requestName", "duration", Name = "MyCustomMetricName")]
+    public static partial Latency CreateLatency(Meter meter);
+
+    // no explicit metric name given, it is auto-generated from the method name
+    [Counter<int>(MetricConstants.EnvironmentName, MetricConstants.Region, MetricConstants.RequestName, MetricConstants.RequestStatus)]
+    public static partial TotalCount CreateTotalCount(Meter meter);
+
+    [Counter<int>]
+    public static partial TotalFailures CreateTotalFailures(this Meter meter);
+}
+//</snippet_Metrics>
+#elif SECOND
+
+using MetricsGen;
+//<snippet_MetricTags>
+using System.Diagnostics.Metrics;
+using Microsoft.Extensions.Diagnostics.Metrics;
+
+public static partial class Metric
+{
+    [Histogram<long>(typeof(MetricTags))]
+    public static partial Latency CreateLatency(Meter meter);
+
+    [Counter<long>(typeof(MetricTags))]
+    public static partial TotalCount CreateTotalCount(Meter meter);
+
+    [Counter<int>(typeof(MetricTags))]
+    public static partial TotalFailures CreateTotalFailures(Meter meter);
+}
+//</snippet_MetricTags>
+#endif

docs/core/diagnostics/snippets/MetricsGen/MetricsGen.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Library</OutputType>
+    <TargetFramework>net9.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Telemetry.Abstractions" Version="9.4.0" />
+  </ItemGroup>
+
+</Project>