Add dotnet csharp

runtimes/default.nix

@@ -53,4 +53,5 @@ args: {
     "emacs" = import ./emacs.nix args;
     "gnat-ada" = import ./gnat-ada.nix args;
     "rust" = import ./rust.nix args;
+    "dotnet-sdk-csharp" = import ./dotnet-sdk-csharp.nix args;
 }

runtimes/dotnet-sdk-csharp.nix

@@ -0,0 +1,81 @@
+{pkgs, piston, ...}:
+let
+    nugetPkg = pkgs.stdenv.mkDerivation {
+        pname = "csharp-nuget-packages";
+        version = pkgs.dotnet-sdk.version;
+
+        dontUnpack = true;
+        dontBuild = true;
+        dontConfigure = true;
+        dontFixup = true;
+        dontPatch = true;
+
+        buildInputs = [
+            pkgs.dotnet-sdk
+        ];
+        installPhase = ''
+            mkdir $out
+            cd $out
+            export HOME=$PWD
+            dotnet new console -o cache_application
+            rm -rf cache_application
+        '';
+    };
+    pkg = pkgs.dotnet-sdk;
+in piston.mkRuntime {
+    language = "csharp";
+    version = pkg.version;
+    runtime = "dotnet-sdk";
+
+    aliases = [
+        "csharp.net"
+        "c#"
+        "cs"
+        "c#.net"
+        "cs.net"
+        "c#-dotnet"
+        "cs-dotnet"
+        "csharp-dotnet"
+        "dotnet-c#"
+        "dotnet-cs"
+        "dotnet-csharp"
+    ];
+
+    compile = ''
+        export HOME=${nugetPkg}
+        ${pkg}/dotnet build --help > /dev/null # Supress welcome message
+        rename 's/$/\.cs/' "$@" # Add .cs extension
+        ${pkg}/dotnet new console -o . --no-restore
+        rm Program.cs
+        ${pkg}/dotnet restore --source ${nugetPkg}/.nuget/packages
+        ${pkg}/dotnet build --no-restore
+    '';
+
+    run = ''
+        export HOME=$PWD
+        shift
+        ${pkg}/dotnet bin/Debug/net6.0/$(basename $(realpath .)).dll "$@"
+    '';
+
+    tests = [
+        (piston.mkTest {
+            files = {
+                "test.cs" = ''
+                    using System;
+
+                    public class Test
+                    {
+                        public static void Main(string[] args)
+                        {
+                            Console.WriteLine(args[0]);
+                        }
+                    }
+                '';
+            };
+            args = ["OK"];
+            stdin = "";
+            packages = [];
+            main = "test.cs";
+        })
+    ];
+}