After installing VS 2015, running csc.exe from command line causes this message to be displayed to console:
This compiler is provided as part of the Microsoft (R) .NET Framework, but only supports language versions up to C# 5, which is no longer the latest version. For compilers that support newer versions of the C# programming language, see http://go.microsoft.com/fwlink/?LinkID=533240
The link redirects to Roslyn's repository at GitHub.
So, is the a way to run "compilers that support newer versions" (Roslyn) from command line?
It sounds like your path is inappropriate, basically. If you open the "Developer Command Prompt for VS2015" you should have $ProgramFiles(x86)$\MSBuild\14.0\bin early in your path - and the csc.exe in there is Roslyn.
I suspect you're running the version in c:\Windows\Microsoft.NET\Framework\4.0.30319 or similar - which is the legacy one, basically.
来源：https://stackoverflow.com/questions/31875825/how-to-run-roslyn-instead-csc-exe-from-command-line