neovim + haskell-language-server setup

default.nix

# nix-env --install --file ./default.nix
let
  nixpkgs = builtins.fetchTarball {
    url    = "https://github.com/NixOS/nixpkgs/archive/c473cc8714710179df205b153f4e9fa007107ff9.tar.gz";
    sha256 = "0q7rnlp1djxc9ikj89c0ifzihl4wfvri3q1bvi75d2wrz844b4lq";
  };

  config = {
    allowUnfree = true;
  };

  ghcVersion = "8107";

  overlay = pkgsNew: pkgsOld: {
    haskell-language-server = pkgsOld.haskell-language-server.override {
      supportedGhcVersions = [ ghcVersion ];
    };

    haskell = pkgsOld.haskell // {
      packages = pkgsOld.haskell.packages // {
        "ghc${ghcVersion}" = pkgsOld.haskell.packages."ghc${ghcVersion}".override (old: {
          overrides =
            pkgsNew.lib.composeExtensions (old.overrides or (_: _: { }))
              (haskellPackagesNew: haskellPackagesOld: {
                ormolu =
                  if pkgsNew.system == "aarch64-darwin"
                  then
                    pkgsNew.haskell.lib.overrideCabal
                      haskellPackagesOld.ormolu
                      (_: { enableSeparateBinOutput = false; })
                  else
                    haskellPackagesOld.ormolu;
              });
        });
      };
    };
  };

  pkgs = import nixpkgs { inherit config; overlays = [ overlay ];};

in
  { inherit (pkgs)
      cabal-install
      cabal2nix
      git
      haskell-language-server
      neovim
      stylish-haskell
    ;
  }

init.nvim

call plug#begin()
Plug 'neovim/nvim-lspconfig'
Plug 'kyazdani42/nvim-web-devicons'
Plug 'folke/trouble.nvim'
call plug#end()

lua << EOF
  local lspconfig = require('lspconfig')

  local on_attach = function(client)
    vim.api.nvim_buf_set_keymap(0, 'n', 'K', '<cmd>lua vim.lsp.buf.hover()<CR>', {noremap = true})
    vim.api.nvim_buf_set_keymap(0, 'n', '<C-n>', '<cmd>lua vim.lsp.diagnostic.goto_next()<CR>', {noremap = true})
    vim.api.nvim_buf_set_keymap(0, 'n', '<C-p>', '<cmd>lua vim.lsp.diagnostic.goto_prev()<CR>', {noremap = true})
    vim.api.nvim_buf_set_option(0, 'omnifunc', 'v:lua.vim.lsp.omnifunc')
    vim.api.nvim_buf_set_option(0, 'tagfunc', 'v:lua.vim.lsp.tagfunc')
    vim.opt.signcolumn = 'yes'
  end

  lspconfig.hls.setup {
    settings = {
      haskell = {
        formattingProvider = 'stylish-haskell',
      },
    },
    on_attach = on_attach,
  }

  local trouble = require("trouble")

  trouble.setup {
  }

  vim.api.nvim_set_keymap("n", "<leader>e", "<cmd>Trouble workspace_diagnostics<cr>", {silent = true, noremap = true})
  vim.api.nvim_set_keymap("n", "<leader>r", "<cmd>Trouble lsp_references<cr>", {silent = true, noremap = true})
EOF

:set nohlsearch
:set expandtab