C# LSP in Helix on macOS

Found myself writing C# in Helix on macOS a bit lately. Weird combination. It took a moment to tweak things so that it all plays nice together.

Helix screenshot showing some C# code with the cursor on a Reverse() call and a popup window displaying the API documentation for Reverse()
Works great once it's configured!

To set up the actual SDK and the language server I did the following.

brew install dotnet
dotnet tool install --global csharp-ls

That puts the tools in place, but I found that running hx --health c-sharp after this step revealed that Helix couldn't find the csharp-ls binary. Adding ~/.dotnet/tools to my $PATH fixed it. 

set -U fish_user_paths $fish_user_paths ~/.dotnet/tools

From here I had a green checkmark in hx --health c-sharp but it still didn't quite work. Inspecting the language server logs in Helix with :log-open, I saw that csharp-ls was unable to find the dotnet SDK. Setting the DOTNET_ROOT environment variable in the language server config in ~/.config/helix/languages.toml fixed this. 

[language-server.csharp]
command = "csharp-ls"
environment = { DOTNET_ROOT = "/opt/homebrew/Cellar/dotnet/10.0.102/libexec" }

This was everything. Annoying that C#'s devtools are so badly integrated with each other and with macOS that you have to manually aim everything at each other like that. But nothing too strenous.