Register Components metrics and tracing by default in WebAssembly when metrics support is enabled

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHostBuilder.cs

@@ -342,5 +342,13 @@ internal void InitializeDefaultServices()
         Services.AddSingleton<AntiforgeryStateProvider, DefaultAntiforgeryStateProvider>();
         RegisterPersistentComponentStateServiceCollectionExtensions.AddPersistentServiceRegistration<AntiforgeryStateProvider>(Services, RenderMode.InteractiveWebAssembly);
         Services.AddSupplyValueFromQueryProvider();
+
+        // Register metrics and tracing by default (opt-out via feature switch for trimming)
+        var isTelemetryDisabled = AppContext.TryGetSwitch("System.Diagnostics.Metrics.Meter.IsSupported", out var switchValue) && switchValue == false;
+        if (!isTelemetryDisabled)
+        {
+            ComponentsMetricsServiceCollectionExtensions.AddComponentsMetrics(Services);
+            ComponentsMetricsServiceCollectionExtensions.AddComponentsTracing(Services);
+        }
     }
 }

src/Components/WebAssembly/WebAssembly/src/Microsoft.AspNetCore.Components.WebAssembly.csproj

@@ -21,6 +21,7 @@
     <Reference Include="Microsoft.Extensions.Configuration.Json" />
     <Reference Include="Microsoft.Extensions.Configuration.Binder" />
     <Reference Include="Microsoft.Extensions.Logging" />
+    <Reference Include="Microsoft.Extensions.Diagnostics" />
     <Reference Include="Microsoft.JSInterop.WebAssembly" />
   </ItemGroup>
 

src/Components/WebAssembly/WebAssembly/test/Hosting/WebAssemblyHostBuilderTest.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.Metrics;
 using System.Text;
 using System.Text.Json;
 using Microsoft.AspNetCore.Components.Routing;
@@ -341,4 +342,21 @@ public void Configuration_IncludesEnvironmentVariables_WhenAddedExplicitly()
             Environment.SetEnvironmentVariable(testEnvVarKey, null);
         }
     }
+
+    [Fact]
+    public void Constructor_RegistersMetricsAndTracingServices()
+    {
+        // Arrange & Act
+        var builder = new WebAssemblyHostBuilder(new TestInternalJSImportMethods());
+        var host = builder.Build();
+
+        // Assert - Verify that IMeterFactory is registered (required for ComponentsMetrics)
+        // and that the service collection was configured for both metrics and tracing
+        var meterFactory = host.Services.GetService<IMeterFactory>();
+        Assert.NotNull(meterFactory);
+
+        // Note: ComponentsActivitySource is scoped and internal, so we can't directly
+        // test for it here, but both AddComponentsMetrics and AddComponentsTracing
+        // are called together, ensuring both telemetry services are registered.
+    }
 }