Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;

namespace GetTypeName
{
    class Program
    {
        static void Main(string[] args)
        {
            var str = GetFullName(typeof(List<int>));
            Console.WriteLine(str);
        }

        private static string GetFullName(Type type)
        {
            var reference = MetadataReference.CreateFromFile(type.Assembly.Location);
            var mscorlb = MetadataReference.CreateFromFile(typeof(Object).Assembly.Location);
            var compilation = CSharpCompilation.Create("test", references: new[] { reference, mscorlb });

            if (type.IsConstructedGenericType)
            {
                var def = type.GetGenericTypeDefinition();
                var args = type.GetGenericArguments();

                var namedType = compilation.GetTypeByMetadataName(def.FullName);
                var typeArguments = args.Select(a
                    => compilation.GetTypeByMetadataName(a.FullName)).ToArray();
                var constructedNamedType = namedType.Construct(typeArguments);
                return constructedNamedType.ToDisplayString();
            }
            else
            {
                var namedType = compilation.GetTypeByMetadataName(type.FullName);
                return namedType.ToDisplayString();
            }

        }
    }
}