Expand generic type fix to handle all open generic types, not just System.Nullable<>

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

Author: Copilot

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_9c97c20c9f124d82999b00e7d24a75b1 : global::TUnit.Core.Interfaces.SourceGenerator.ITestSource
+internal sealed class Tests_SimpleTest_TestSource_38be5ee0b5554088ba7b233e82649e27 : 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)
     {
@@ -18,7 +18,7 @@ internal sealed class Tests_SimpleTest_TestSource_9c97c20c9f124d82999b00e7d24a75
             AttributeFactory = () =>
             [
                 new global::TUnit.Core.TestAttribute(),
-                new global::TUnit.TestProject.Bugs._2971.SomeAttribute(typeof(T?))
+                new global::TUnit.TestProject.Bugs._2971.SomeAttribute(typeof(global::System.Nullable<>))
             ],
             DataSources = new global::TUnit.Core.IDataSourceAttribute[]
             {
@@ -84,11 +84,11 @@ internal sealed class Tests_SimpleTest_TestSource_9c97c20c9f124d82999b00e7d24a75
         yield break;
     }
 }
-internal static class Tests_SimpleTest_ModuleInitializer_9c97c20c9f124d82999b00e7d24a75b1
+internal static class Tests_SimpleTest_ModuleInitializer_38be5ee0b5554088ba7b233e82649e27
 {
     [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_9c97c20c9f124d82999b00e7d24a75b1());
+        global::TUnit.Core.SourceRegistrar.Register(typeof(global::TUnit.TestProject.Bugs._2971.Tests), new Tests_SimpleTest_TestSource_38be5ee0b5554088ba7b233e82649e27());
     }
 }

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

@@ -24,17 +24,6 @@ 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

@@ -208,35 +208,32 @@ public static bool EnumerableGenericTypeIs(this ITypeSymbol enumerable, Generato
 
     public static string GloballyQualified(this ISymbol typeSymbol)
     {
-        // Special handling for System.Nullable<> generic type definition
-        // When Roslyn encounters System.Nullable<>, it displays it as "T?" which is not valid C# syntax
-        if (typeSymbol is INamedTypeSymbol namedTypeSymbol)
+        // Handle open generic types where type arguments are type parameters
+        // This prevents invalid C# like List<T>, Dictionary<TKey, TValue>, T? where type parameters are undefined
+        if (typeSymbol is INamedTypeSymbol namedTypeSymbol && namedTypeSymbol.IsGenericType)
         {
-            // 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)
+            // Check if this is an unbound generic type or has type parameter arguments
+            bool hasTypeParameters = namedTypeSymbol.TypeArguments.Any(t => t.TypeKind == TypeKind.TypeParameter);
+            bool isUnboundGeneric = namedTypeSymbol.IsUnboundGenericType;
+            
+            if (hasTypeParameters || isUnboundGeneric)
             {
-                // 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)
+                // Special case for System.Nullable<> - Roslyn displays it as "T?" even for open generic
+                if (namedTypeSymbol.SpecialType == SpecialType.System_Nullable_T ||
+                    namedTypeSymbol.ConstructedFrom?.SpecialType == SpecialType.System_Nullable_T)
                 {
                     return "global::System.Nullable<>";
                 }
+                
+                // General case for other open generic types
+                var typeBuilder = new StringBuilder(typeSymbol.ToDisplayString(DisplayFormats.FullyQualifiedNonGenericWithGlobalPrefix));
+                typeBuilder.Append('<');
+                typeBuilder.Append(new string(',', namedTypeSymbol.TypeArguments.Length - 1));
+                typeBuilder.Append('>');
+
+                return typeBuilder.ToString();
             }
         }
-        
-        // Only generate open generic form for types with unresolved type parameters
-        // This ensures we get BaseClass<> for generic definitions but List<int> for constructed types
-        if(typeSymbol is INamedTypeSymbol { IsGenericType: true } namedTypeSymbol2 && 
-           namedTypeSymbol2.TypeArguments.Any(t => t.TypeKind == TypeKind.TypeParameter))
-        {
-            var typeBuilder = new StringBuilder(typeSymbol.ToDisplayString(DisplayFormats.FullyQualifiedNonGenericWithGlobalPrefix));
-            typeBuilder.Append('<');
-            typeBuilder.Append(new string(',', namedTypeSymbol2.TypeArguments.Length - 1));
-            typeBuilder.Append('>');
-
-            return typeBuilder.ToString();
-        }
 
         return typeSymbol.ToDisplayString(DisplayFormats.FullyQualifiedGenericWithGlobalPrefix);
     }