Unconditionally enable the regex during development (linker will still trim it unless enabled on the project)

Author: javiercn

src/Components/Components/src/Routing/RegexConstraintSupport.cs

@@ -5,6 +5,11 @@ namespace Microsoft.AspNetCore.Components.Routing;
 
 internal static class RegexConstraintSupport
 {
-    public static bool IsEnabled =>
-        AppContext.TryGetSwitch("Microsoft.AspNetCore.Components.Routing.RegexConstraintSupport", out var enabled) && enabled;
+    // We should check the AppContext switch in the implementation, but it doesn't flow to the wasm runtime
+    // during development, so we can't offer a better experience (build time message to enable the switch)
+    // until the context switch flows to the runtime.
+    // This value gets updated by the linker when the app is trimmed, so the code will always be removed from
+    // webassembly unless the switch is enabled.
+    public static bool IsEnabled => true;
+        // AppContext.TryGetSwitch("Microsoft.AspNetCore.Components.Routing.RegexConstraintSupport", out var enabled) && enabled;
 }

src/Components/test/testassets/Components.TestServer/Components.TestServer.csproj

@@ -7,8 +7,17 @@
     <BlazorWebAssemblyLoadAllGlobalizationData>true</BlazorWebAssemblyLoadAllGlobalizationData>
     <Nullable>annotations</Nullable>
     <RazorLangVersion>latest</RazorLangVersion>
+    <BlazorRoutingEnableRegexConstraint>true</BlazorRoutingEnableRegexConstraint>
+    <BlazorRoutingEnableRegexConstraint Condition="'$(BlazorRoutingEnableRegexConstraint)' == ''">false</BlazorRoutingEnableRegexConstraint>
   </PropertyGroup>
 
+  <ItemGroup>
+    <RuntimeHostConfigurationOption Include="Microsoft.AspNetCore.Components.Routing.RegexConstraintSupport"
+      Condition="'$(BlazorRoutingEnableRegexConstraint)' != ''"
+      Value="$(BlazorRoutingEnableRegexConstraint)"
+      Trim="true" />
+</ItemGroup>
+
   <ItemGroup>
     <Reference Include="Microsoft.AspNetCore" />
     <Reference Include="Microsoft.AspNetCore.Authentication.Cookies" />