Add extension to simplify negating an IncrementalValueProvider<bool>

src/SafeRouting.Generator/IncrementalValueProviderExtensions.cs

@@ -0,0 +1,9 @@
+using Microsoft.CodeAnalysis;
+
+namespace SafeRouting.Generator;
+
+public static class IncrementalValueProviderExtensions
+{
+  public static IncrementalValueProvider<bool> Not(this IncrementalValueProvider<bool> source)
+    => source.Select(static (x, _) => !x);
+}

src/SafeRouting.Generator/RouteGenerator.cs

@@ -28,10 +28,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
       var isSupportedLanguageVersionProvider = languageVersionProvider
         .Select(static (x, _) => x >= LanguageVersion.CSharp8);
 
-      var isUnsupportedLanguageVersionProvider = isSupportedLanguageVersionProvider
-        .Select(static (x, _) => !x);
-
-      context.RegisterConditionalOutput(isUnsupportedLanguageVersionProvider, static context =>
+      context.RegisterConditionalOutput(isSupportedLanguageVersionProvider.Not(), static context =>
       {
         context.ReportDiagnostic(Diagnostics.CreateUnsupportedLanguageVersionDiagnostic());
       });