Haskell Language Server and Coc

Haskell has great IDE support via Haskell Language Server or HLS.

Coc.nvim is the recommended extension to get Language Server Protocol (LSP) support for editing Haskell in neovim.

It turns out that home-manager has a module that, unlike the NixOS version, provides a declarative way to install and configure coc.nvim with Haskell support (EDIT: this is language-independent):

{
  programs.neovim = {
    coc = {
      enable = true;
      settings = {
        languageserver = {
          haskell = {
            command = "haskell-language-server-wrapper";
            args = [ "--lsp" ];
            rootPatterns = [
              "*.cabal"
              "cabal.project"
              "hie.yaml"
            ];
            filetypes = [ "haskell" "lhaskell" ];
          };
        };
      };
    };
  };
}

https://github.com/srid/nixos-config/commit/9a6410331063ae97ae405837559cf4c5b3990ada

It does work when trying out in the nix-shell of haskell-template.

Declarative plugin config in Nix

The above is neat—no need to hand-write VimScript or Lua just to configure the extension. Can we do the same for other neovim extensions in Nix? A couple of attempts exist: nix-neovim and NixVim.