Fix #2312: Constructors and operators may not have any generic type parameters in C#

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataMethod.cs

@@ -66,21 +66,28 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			this.symbolKind = SymbolKind.Method;
 			var (accessorOwner, semanticsAttribute) = module.PEFile.MethodSemanticsLookup.GetSemantics(handle);
 			const MethodAttributes finalizerAttributes = (MethodAttributes.Virtual | MethodAttributes.Family | MethodAttributes.HideBySig);
+			this.typeParameters = MetadataTypeParameter.Create(module, this, def.GetGenericParameters());
 			if (semanticsAttribute != 0)
 			{
 				this.symbolKind = SymbolKind.Accessor;
 				this.accessorOwner = accessorOwner;
 				this.AccessorKind = semanticsAttribute;
 			}
-			else if ((attributes & (MethodAttributes.SpecialName | MethodAttributes.RTSpecialName)) != 0)
+			else if ((attributes & (MethodAttributes.SpecialName | MethodAttributes.RTSpecialName)) != 0
+				&& typeParameters.Length == 0)
 			{
 				string name = this.Name;
 				if (name == ".cctor" || name == ".ctor")
+				{
 					this.symbolKind = SymbolKind.Constructor;
-				else if (name.StartsWith("op_", StringComparison.Ordinal))
+				}
+				else if (name.StartsWith("op_", StringComparison.Ordinal)
+					&& CSharp.Syntax.OperatorDeclaration.GetOperatorType(name) != null)
+				{
 					this.symbolKind = SymbolKind.Operator;
+				}
 			}
-			else if ((attributes & finalizerAttributes) == finalizerAttributes)
+			else if ((attributes & finalizerAttributes) == finalizerAttributes && typeParameters.Length == 0)
 			{
 				if (Name == "Finalize" && Parameters.Count == 0 && ReturnType.IsKnownType(KnownTypeCode.Void)
 					&& (DeclaringTypeDefinition as MetadataTypeDefinition)?.Kind == TypeKind.Class)
@@ -88,7 +95,6 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 					this.symbolKind = SymbolKind.Destructor;
 				}
 			}
-			this.typeParameters = MetadataTypeParameter.Create(module, this, def.GetGenericParameters());
 			this.IsExtensionMethod = (attributes & MethodAttributes.Static) == MethodAttributes.Static
 				&& (module.TypeSystemOptions & TypeSystemOptions.ExtensionMethods) == TypeSystemOptions.ExtensionMethods
 				&& def.GetCustomAttributes().HasKnownAttribute(metadata, KnownAttribute.Extension);