Fix gettype unbound generics #1165

CodeConverter/CSharp/ExpressionNodeVisitor.cs

@@ -578,8 +578,13 @@ public override async Task<CSharpSyntaxNode> VisitArrayRankSpecifier(VBasic.Synt
 
     public override async Task<CSharpSyntaxNode> VisitTypeArgumentList(VBasic.Syntax.TypeArgumentListSyntax node)
     {
-        var args = await node.Arguments.SelectAsync(async a => await a.AcceptAsync<TypeSyntax>(TriviaConvertingExpressionVisitor));
-        return CS.SyntaxFactory.TypeArgumentList(CS.SyntaxFactory.SeparatedList(args));
+        var args = await node.Arguments.SelectAsync(async a => {
+            if (a is VBasic.Syntax.IdentifierNameSyntax id && id.Identifier.IsMissing) {
+                return CS.SyntaxFactory.OmittedTypeArgument();
+            }
+            return await a.AcceptAsync<TypeSyntax>(TriviaConvertingExpressionVisitor);
+        });
+        return CS.SyntaxFactory.TypeArgumentList(CS.SyntaxFactory.SeparatedList<TypeSyntax>(args));
     }
 
     private async Task<CSharpSyntaxNode> ConvertCastExpressionAsync(VBSyntax.CastExpressionSyntax node,

CodeConverter/CSharp/VbNameExpander.cs

@@ -110,6 +110,9 @@ private static bool NameCanBeExpanded(SyntaxNode node)
         if (node.Parent is NameColonEqualsSyntax || node.Parent is NamedFieldInitializerSyntax) return false;
         // Workaround roslyn bug where it duplicates the inferred name
         if (node.Parent is InferredFieldInitializerSyntax) return false;
+        // Roslyn's Simplifier.Expand corrupts open generic type arguments (e.g. Nullable(Of) in GetType(Nullable(Of)))
+        // by replacing them with the error type fallback (Object). Prevent expansion so the missing type arg is preserved.
+        if (node is GenericNameSyntax gns && gns.TypeArgumentList.Arguments.Any(a => a is IdentifierNameSyntax id && id.Identifier.IsMissing)) return false;
         return true;
     }
 

Tests/CSharp/ExpressionTests/OmittedTypeArgumentTest.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Threading.Tasks;
+using ICSharpCode.CodeConverter.Tests.TestRunners;
+using Xunit;
+
+namespace ICSharpCode.CodeConverter.Tests.CSharp.ExpressionTests;
+
+public class OmittedTypeArgumentTest : ConverterTestBase
+{
+    [Fact]
+    public async Task TestGetTypeOmittedArgument()
+    {
+        await TestConversionVisualBasicToCSharpAsync(@"Public Class Test
+    Public Function IsNullable(ByVal type As Type) As Boolean
+        Return type.IsGenericType AndAlso type.GetGenericTypeDefinition() Is GetType(Nullable(Of))
+    End Function
+End Class", @"using System;
+
+public partial class Test
+{
+    public bool IsNullable(Type @type)
+    {
+        return type.IsGenericType && ReferenceEquals(type.GetGenericTypeDefinition(), typeof(Nullable<>));
+    }
+}");
+    }
+}