Fix BlazorWebAssemblyDiagnosticsEnabled so it can be set from a .csproj

src/BlazorWasmSdk/Targets/Microsoft.NET.Sdk.BlazorWebAssembly.Current.props

@@ -36,18 +36,6 @@ Copyright (c) .NET Foundation. All rights reserved.
 
     <!-- Regex route constraint support for Blazor routing -->
     <BlazorRoutingEnableRegexConstraint Condition="'$(BlazorRoutingEnableRegexConstraint)' == ''">false</BlazorRoutingEnableRegexConstraint>
-
-    <!--
-      Enable diagnostics infrastructure (metrics, event sources, and HTTP activity propagation) by default for Blazor
-      WebAssembly apps. The low-level WASM runtime defaults these to 'false' to reduce download size via aggressive
-      trimming, but Blazor apps commonly use HttpClient with distributed tracing, structured logging, and metrics
-      (especially with .NET Aspire). Developers who want smaller binaries can opt out by setting
-      BlazorWebAssemblyDiagnosticsEnabled to 'false' or by setting the individual properties explicitly.
-    -->
-    <BlazorWebAssemblyDiagnosticsEnabled Condition="'$(BlazorWebAssemblyDiagnosticsEnabled)' == ''">true</BlazorWebAssemblyDiagnosticsEnabled>
-    <MetricsSupport Condition="'$(MetricsSupport)' == '' and '$(BlazorWebAssemblyDiagnosticsEnabled)' == 'true'">true</MetricsSupport>
-    <EventSourceSupport Condition="'$(EventSourceSupport)' == '' and '$(BlazorWebAssemblyDiagnosticsEnabled)' == 'true'">true</EventSourceSupport>
-    <HttpActivityPropagationSupport Condition="'$(HttpActivityPropagationSupport)' == '' and '$(BlazorWebAssemblyDiagnosticsEnabled)' == 'true'">true</HttpActivityPropagationSupport>
   </PropertyGroup>
 
   <Import Sdk="Microsoft.NET.Sdk.Razor" Project="Sdk.props" />

src/BlazorWasmSdk/Targets/Microsoft.NET.Sdk.BlazorWebAssembly.Current.targets

@@ -23,6 +23,22 @@ Copyright (c) .NET Foundation. All rights reserved.
 
     <!-- EnableConfigurationBindingGenerator is enabled by default for trimmed apps, but Blazor WASM disables it by default -->
     <EnableConfigurationBindingGenerator Condition="'$(EnableConfigurationBindingGenerator)' == ''">false</EnableConfigurationBindingGenerator>
+
+    <!--
+      Enable diagnostics infrastructure (metrics, event sources, and HTTP activity propagation) by default for Blazor
+      WebAssembly apps. The low-level WASM runtime defaults these to 'false' to reduce download size via aggressive
+      trimming, but Blazor apps commonly use HttpClient with distributed tracing, structured logging, and metrics
+      (especially with .NET Aspire). Developers who want smaller binaries can opt out by setting
+      BlazorWebAssemblyDiagnosticsEnabled to 'false' or by setting the individual properties explicitly.
+
+      These defaults are evaluated at Sdk.targets time (rather than Sdk.props time) so that the values can be set from
+      the project body of a .csproj, which is read before the SDK targets are imported. They must also be configured
+      before the feature switches are initialized to 'false' by the imported SDK targets below.
+    -->
+    <BlazorWebAssemblyDiagnosticsEnabled Condition="'$(BlazorWebAssemblyDiagnosticsEnabled)' == ''">true</BlazorWebAssemblyDiagnosticsEnabled>
+    <MetricsSupport Condition="'$(MetricsSupport)' == '' and '$(BlazorWebAssemblyDiagnosticsEnabled)' == 'true'">true</MetricsSupport>
+    <EventSourceSupport Condition="'$(EventSourceSupport)' == '' and '$(BlazorWebAssemblyDiagnosticsEnabled)' == 'true'">true</EventSourceSupport>
+    <HttpActivityPropagationSupport Condition="'$(HttpActivityPropagationSupport)' == '' and '$(BlazorWebAssemblyDiagnosticsEnabled)' == 'true'">true</HttpActivityPropagationSupport>
   </PropertyGroup>
 
   <Import Sdk="Microsoft.NET.Sdk.Razor" Project="Sdk.targets" />

test/Microsoft.NET.Sdk.BlazorWebAssembly.Tests/VanillaWasmTests.cs

@@ -43,11 +43,26 @@ public void Build_Works()
 
         [TestMethod]
         [CoreMSBuildOnly]
-        [DataRow(null, "true", "true")]
-        [DataRow("false", "false", "false")]
-        public void Build_ResolvesBlazorDiagnosticsFeatureSwitches(string diagnosticsEnabled, string expectedDiagnosticsEnabled, string expectedFeatureValue)
+        [DataRow(null, false, "true", "true")]
+        [DataRow("false", false, "false", "false")]
+        // Setting the property from the project body must take effect (dotnet/sdk#55489): the defaults are
+        // evaluated at Sdk.targets time so a value set in the .csproj is honored, not just a global property.
+        [DataRow("false", true, "false", "false")]
+        [DataRow("true", true, "true", "true")]
+        public void Build_ResolvesBlazorDiagnosticsFeatureSwitches(string diagnosticsEnabled, bool setInProjectFile, string expectedDiagnosticsEnabled, string expectedFeatureValue)
         {
             var testInstance = CreateAspNetSdkTestAsset("BlazorWasmMinimal");
+
+            if (setInProjectFile && diagnosticsEnabled is not null)
+            {
+                testInstance.WithProjectChanges((project, doc) =>
+                {
+                    var propertyGroup = new XElement("PropertyGroup");
+                    propertyGroup.Add(new XElement("BlazorWebAssemblyDiagnosticsEnabled", diagnosticsEnabled));
+                    doc.Root.Add(propertyGroup);
+                });
+            }
+
             var build = CreateBuildCommand(testInstance);
 
             var arguments = new List<string>
@@ -58,7 +73,7 @@ public void Build_ResolvesBlazorDiagnosticsFeatureSwitches(string diagnosticsEna
                 "-getProperty:HttpActivityPropagationSupport"
             };
 
-            if (diagnosticsEnabled is not null)
+            if (!setInProjectFile && diagnosticsEnabled is not null)
             {
                 arguments.Add($"/p:BlazorWebAssemblyDiagnosticsEnabled={diagnosticsEnabled}");
             }