Bring in the Mono C# compiler backend

[Chuck]

In April 2008, the Mono C# 2.0 compiler was released under the unrestrictive MIT license. Previous versions had been under GPL which was not compatible with Cobra's MIT license (we would have had to change it).

See  http://www.mono-project.com/news/archive/2008/Apr-08.html

I believe the initial approach we can take for this ticket is the following:

• Get the Mono mcs.exe compiler rebuilt as mono-sharp.dll
• Ensure that mono-sharp.dll has public API calls to compile source code from memory (a .NET string) and to take options.
  • That eliminates disk I/O.
• Have cobra.exe reference mono-sharp.dll and invoke it.
  • That eliminates process launching.

The ability to generate C# to disk and invoke the compiler should be left in place for some time in case we find ourselves in need of it.

[Chuck]

I think this is better than writing an IL backend due to the advantages of leverage. A lot of work has been put into their compiler; no need to reinvent the wheel if backends are now becoming commodities.

[Chuck]

This may be easier than I thought:

• In 2008 Miguel de Icaza turned the compiler into a reusable library (Mono.CSharp.dll) and introduced the Interactive C# Shell. --  http://www.mono-project.com/CSharp_Compiler
•  http://www.go-mono.com/docs/index.aspx?link=N%3AMono.CSharp

But it might not work so well on .NET:

•  http://n2.nabble.com/Mono.CSharp.dll-on-original-Microsoft-.NET-td1585138.html

Also, note that since the Mono compiler went to the MIT license in 2008, it may not be possible to do this for .NET 2.0.

[Chuck]

Btw it was starting with Mono 2.0 that the Mono C# compiler went to MIT license.

[Chuck]

Another mention of the C# DLL is here:
 http://www.mono-project.com/Release_Notes_Mono_2.2

[Chuck]

Note that .NET can treat .NET .exe files as libraries/assemblies. So you can, for example, load gmcs.exe as an assembly with Assembly.loadFile at run-time. You could also ref it at compile-time, but I think you would then have to put it in the GAC or copy it to your local directory.

[Chuck]

This is actually done on the *nix/Mono side with a wee bit of hacking on the Mono source code. However, the Mono C# compiler won't run under the Microsoft CLR which is kind of strange given that the Mono C# compiler is a CLR program producing CLR programs. There are some internal things they do that MS chokes on. However, we may be able to fix this by hacking on their compiler some more.