private static bool IsExtensionMethod(MethodDeclarationSyntax methodDeclaration)
        {
            if (!methodDeclaration.IsParentKind(SyntaxKind.ClassDeclaration) ||
                !((ClassDeclarationSyntax)methodDeclaration.Parent).Modifiers.Any(SyntaxKind.StaticKeyword))
            {
                return false;
            }

            if (methodDeclaration.ParameterList == null ||
                methodDeclaration.ParameterList.Parameters.Count == 0)
            {
                return false;
            }

            return methodDeclaration.ParameterList.Parameters[0].Modifiers.Any(SyntaxKind.ThisKeyword);
        }