Question

I was under the impression Mono’s compiler was usable in Microsoft.NET

edit: updated blog posting here that I originally missed that explains some of it (is consistent with Justin’s answers)

I created a simple class to try to use it

[TestFixture]
class Class1
{
    [Test]
    public void EXPR()
    {
        Evaluator.Run("using System;");

        int sum = (int)Evaluator.Evaluate("1+2");

    }
}

And a project in Visual Studio 2010 that references C:\Program Files (x86)\Mono-2.10.1\lib\mono\4.0\Mono.CSharp.dll.

However when I try to run this task I get the following exception, thrown at the Evaluator.Run call:

    System.TypeInitializationException was unhandled by user code
      Message=The type initializer for 'Mono.CSharp.Evaluator' threw an exception.
      Source=Mono.CSharp
      TypeName=Mono.CSharp.Evaluator
      StackTrace:
           at Mono.CSharp.Evaluator.Run(String statement)
           at Experiments.Class1.EXPR() in W:\Experiments\Class1.cs:line 16
      InnerException: System.TypeLoadException
           Message=Method 'Mono.CSharp.Location.ToString()' is security transparent, but is a member of a security critical type.
           Source=Mono.CSharp
           TypeName=Mono.CSharp.Location.ToString()
           StackTrace:
                at Mono.CSharp.Evaluator..cctor()
           InnerException: 

A google confirms one other person asking this question but no answer. I tried to start reading the microsoft article on security transparent code but got confused quite quickly. Would someone be able to suggest a quick workaround to allow me to use this? And possibly summarise the security implications, if any, to me (in the context of my situation – in the future I hope to package it with a thick client application, to be used both internally and by end-users)

Answer 1

It looks like this is a bug in Mono.

.NET 4 abandoned Code Access Security but kept the concept of Security Transparent Code. In a nutshell, low-level code that does stuff, like call unmanaged code, must be “security critical”. Application level code is marked “transparent”. “Transparent” code cannot call into “security critical” code.

It sounds like Mono.CSharp.Location.ToString() needs to be marked with the [SecuritySafeCritical] attribute if you want the Mono 2.10 code to work with .NET 4. Maybe even better would be marking all of Mono.CSharp as SecuritySafeCritical.

http://msdn.microsoft.com/en-us/library/system.security.securitycriticalattribute.aspx

PS. Sorry to have multiple answers for one question. After I realized that 2.11 would work, I became more curious about what the error with 2.10 meant. I cannot really combine this answer with the others.