Using Roslyn for a new language implementation
I know this is an old thread, but your best bet (in visual studio at least) is to create an IVsSingleFileGenerator that converts your code into c# or other Roslyn language.
Roslyn does not allow to do it.
Look at this project: Nitra. It's under active development.
Roslyn is not meant for this.
The best you'll be able to do with Roslyn is generate a C# (or VB) SyntaxTree & Compilation after you parse your language by hand, letting Roslyn take care of the type system & codegen.
And this will only work at all if your language can be completely translated to C# (or VB) syntax.