Add targeted fix in TypedConstantFormatter for System.Nullable<>

Co-authored-by: thomhurst <30480171+thomhurst@users.noreply.github.com>

TUnit.Core.SourceGenerator.Tests/Bugs2971NullableTypeTest.Test.verified.txt

@@ -5,7 +5,7 @@
 #pragma warning disable
 #nullable enable
 namespace TUnit.Generated;
-internal sealed class Tests_SimpleTest_TestSource_21ec244a5088444d90b98db3ae4e625e : global::TUnit.Core.Interfaces.SourceGenerator.ITestSource
+internal sealed class Tests_SimpleTest_TestSource_49ae2d23fddf49e799c37799159949b0 : global::TUnit.Core.Interfaces.SourceGenerator.ITestSource
 {
     public async global::System.Collections.Generic.IAsyncEnumerable<global::TUnit.Core.TestMetadata> GetTestsAsync(string testSessionId, [global::System.Runtime.CompilerServices.EnumeratorCancellation] global::System.Threading.CancellationToken cancellationToken = default)
     {
@@ -84,11 +84,11 @@ internal sealed class Tests_SimpleTest_TestSource_21ec244a5088444d90b98db3ae4e62
         yield break;
     }
 }
-internal static class Tests_SimpleTest_ModuleInitializer_21ec244a5088444d90b98db3ae4e625e
+internal static class Tests_SimpleTest_ModuleInitializer_49ae2d23fddf49e799c37799159949b0
 {
     [global::System.Runtime.CompilerServices.ModuleInitializer]
     public static void Initialize()
     {
-        global::TUnit.Core.SourceRegistrar.Register(typeof(global::TUnit.TestProject.Bugs._2971.Tests), new Tests_SimpleTest_TestSource_21ec244a5088444d90b98db3ae4e625e());
+        global::TUnit.Core.SourceRegistrar.Register(typeof(global::TUnit.TestProject.Bugs._2971.Tests), new Tests_SimpleTest_TestSource_49ae2d23fddf49e799c37799159949b0());
     }
 }

TUnit.Core.SourceGenerator/CodeGenerators/Formatting/TypedConstantFormatter.cs

@@ -24,6 +24,17 @@ public string FormatForCode(TypedConstant constant, ITypeSymbol? targetType = nu
 
             case TypedConstantKind.Type:
                 var type = (ITypeSymbol)constant.Value!;
+
+                // Special handling for System.Nullable<> when it would be displayed as "T?"
+                if (type is INamedTypeSymbol namedType &&
+                    (namedType.SpecialType == SpecialType.System_Nullable_T ||
+                     namedType.ConstructedFrom?.SpecialType == SpecialType.System_Nullable_T) &&
+                    namedType.TypeArguments.Length == 1 &&
+                    namedType.TypeArguments[0].TypeKind == TypeKind.TypeParameter)
+                {
+                    return "typeof(global::System.Nullable<>)";
+                }
+
                 return $"typeof({type.GloballyQualified()})";
 
             case TypedConstantKind.Array:

TUnit.Core.SourceGenerator/Extensions/TypeExtensions.cs

@@ -208,17 +208,20 @@ public static bool EnumerableGenericTypeIs(this ITypeSymbol enumerable, Generato
 
     public static string GloballyQualified(this ISymbol typeSymbol)
     {
-        // Special handling for System.Nullable<> generic type definition first
+        // Special handling for System.Nullable<> generic type definition
         // When Roslyn encounters System.Nullable<>, it displays it as "T?" which is not valid C# syntax
-        // Only apply this to the open generic type definition, not constructed types like Nullable<int>
         if (typeSymbol is INamedTypeSymbol namedTypeSymbol)
         {
-            // Check if this is the System.Nullable<> generic type definition with a type parameter
-            if ((namedTypeSymbol.SpecialType == SpecialType.System_Nullable_T || 
-                namedTypeSymbol.ConstructedFrom?.SpecialType == SpecialType.System_Nullable_T) &&
-                namedTypeSymbol.TypeArguments.Any(t => t.TypeKind == TypeKind.TypeParameter))
+            // Check if this is System.Nullable<T> where T is unbound/type parameter
+            if (namedTypeSymbol.SpecialType == SpecialType.System_Nullable_T ||
+                namedTypeSymbol.ConstructedFrom?.SpecialType == SpecialType.System_Nullable_T)
             {
-                return "global::System.Nullable<>";
+                // For the unbound generic case like System.Nullable<> or Nullable<T> where T is a type parameter
+                if (namedTypeSymbol.TypeArguments.Length == 1 && 
+                    namedTypeSymbol.TypeArguments[0].TypeKind == TypeKind.TypeParameter)
+                {
+                    return "global::System.Nullable<>";
+                }
             }
         }