Use .NET SDK instead of Mono for compiling C# programs

[Jisu-Woniu]

Traditionally, most online judge systems use Mono to compile and run C# programs.

This leads to several problems:

• Mono, even with its latest version, only support C# 7.2, which was released back in 2017.
• The official repository of Mono only support Debian 10 and Ubuntu 20.04 and earlier versions of system.

.NET SDK is widely used in modern C# development, but it does not provide an out-of-box C# file compiler.

Based on this answer from Stack Overflow, I can compile single C# file with the following script.

[Jisu-Woniu]

#!/bin/bash
: "${DOTNET_ROOT:=$(dirname "$(dirname "$(dotnet --info | grep "Base Path" | awk '{ print $NF }')")")}"
csc_path=$(find "$DOTNET_ROOT" -name csc.dll -print | sort -V | tail -n1)
ref_path=$(find "$DOTNET_ROOT" -path "*packs/Microsoft.NETCore.App.Ref/*/ref" -print | sort -V | tail -n1)
read -r -a refs <<<"$(find "$ref_path" -path '*.dll' -printf "-r:%p ")"

# Compile C# source file into '.exe' file.
csc() {
  dotnet "$csc_path" -nologo "${refs[@]}" "$@"
}

dotnet_csc_runtimeconfig="$HOME/.cache/csc-console-apps.runtimeconfig.json"

dotnet_runtime_version=$(dotnet --list-runtimes | grep "Microsoft\.NETCore\.App" | sort -V | tail -n1 | awk '{ print $2 }')
cat <<EOF >"$dotnet_csc_runtimeconfig"
{
  "runtimeOptions": {
    "framework": {
      "name": "Microsoft.NETCore.App",
      "version": "$dotnet_runtime_version"
    }
  }
}
EOF

# Run compiled C# '.exe'.
csc-run() {
  dotnet exec --runtimeconfig "$dotnet_csc_runtimeconfig" "$@"
}

echo "Help:"
echo "Use 'csc <SOURCE>.cs' to compile a C# file into '.exe' file."
echo "Use 'csc-run <OUTPUT>.exe' to run a compiled C# '.exe'."