Rework haskell to allow both hls and haskell-tools language servers

modules/plugins/languages/haskell.nix

@@ -4,63 +4,68 @@
   pkgs,
   ...
 }: let
-  inherit (builtins) isList attrNames;
+  inherit (builtins) isList attrNames elem;
   inherit (lib.types) either package enum listOf str;
   inherit (lib.options) mkEnableOption mkOption;
   inherit (lib.strings) optionalString;
   inherit (lib.modules) mkIf mkMerge;
   inherit (lib.nvim.types) mkGrammarOption;
   inherit (lib.nvim.dag) entryAfter;
   inherit (lib.nvim.lua) toLuaObject;
-  inherit (lib.meta) getExe';
+  inherit (lib.nvim.attrsets) mapListToAttrs;
   inherit (lib.generators) mkLuaInline;
   inherit (pkgs) haskellPackages;
 
   cfg = config.vim.languages.haskell;
 
-  defaultServers = ["hls"];
+  defaultServers = ["haskell-tools"];
+  serverCommon = {
+    filetypes = ["haskell" "lhaskell"];
+    root_dir =
+      mkLuaInline
+      /*
+      lua
+      */
+      ''
+        function(bufnr, on_dir)
+          local fname = vim.api.nvim_buf_get_name(bufnr)
+          on_dir(util.root_pattern('hie.yaml', 'stack.yaml', 'cabal.project', '*.cabal', 'package.yaml')(fname))
+        end
+      '';
+  };
   servers = {
-    hls = {
-      enable = false;
-      cmd = [(getExe' pkgs.haskellPackages.haskell-language-server "haskell-language-server-wrapper") "--lsp"];
-      filetypes = ["haskell" "lhaskell"];
-      on_attach =
-        mkLuaInline
-        /*
-        lua
-        */
-        ''
-          function(client, bufnr)
-              local ht = require("haskell-tools")
-              local opts = { noremap = true, silent = true, buffer = bufnr }
-              vim.keymap.set('n', '<localleader>cl', vim.lsp.codelens.run, opts)
-              vim.keymap.set('n', '<localleader>hs', ht.hoogle.hoogle_signature, opts)
-              vim.keymap.set('n', '<localleader>ea', ht.lsp.buf_eval_all, opts)
-              vim.keymap.set('n', '<localleader>rr', ht.repl.toggle, opts)
-              vim.keymap.set('n', '<localleader>rf', function()
-                ht.repl.toggle(vim.api.nvim_buf_get_name(0))
-              end, opts)
-              vim.keymap.set('n', '<localleader>rq', ht.repl.quit, opts)
-            end
-        '';
-      root_dir =
-        mkLuaInline
-        /*
-        lua
-        */
-        ''
-          function(bufnr, on_dir)
-            local fname = vim.api.nvim_buf_get_name(bufnr)
-            on_dir(util.root_pattern('hie.yaml', 'stack.yaml', 'cabal.project', '*.cabal', 'package.yaml')(fname))
-          end
-        '';
-      settings = {
-        haskell = {
-          formattingProvider = "ormolu";
-          cabalFormattingProvider = "cabalfmt";
-        };
+    hls =
+      serverCommon
+      // {
+        enable = true;
+        cmd = ["haskell-language-server-wrapper" "--lsp"];
+      };
+
+    haskell-tools =
+      serverCommon
+      // {
+        # haskell-tools is already started by haskell-tools.nvim via ftplugin
+        enable = false;
+        on_attach =
+          mkLuaInline
+          /*
+          lua
+          */
+          ''
+            function(client, bufnr)
+                local ht = require("haskell-tools")
+                local opts = { noremap = true, silent = true, buffer = bufnr }
+                vim.keymap.set('n', '<localleader>cl', vim.lsp.codelens.run, opts)
+                vim.keymap.set('n', '<localleader>hs', ht.hoogle.hoogle_signature, opts)
+                vim.keymap.set('n', '<localleader>ea', ht.lsp.buf_eval_all, opts)
+                vim.keymap.set('n', '<localleader>rr', ht.repl.toggle, opts)
+                vim.keymap.set('n', '<localleader>rf', function()
+                  ht.repl.toggle(vim.api.nvim_buf_get_name(0))
+                end, opts)
+                vim.keymap.set('n', '<localleader>rq', ht.repl.quit, opts)
+              end
+          '';
       };
-    };
   };
 in {
   options.vim.languages.haskell = {
@@ -98,7 +103,26 @@ in {
       };
     })
 
-    (mkIf (cfg.dap.enable || cfg.lsp.enable) {
+    (mkIf cfg.lsp.enable {
+      vim.lsp.servers =
+        mapListToAttrs (n: {
+          name = n;
+          value = servers.${n};
+        })
+        cfg.lsp.servers;
+    })
+
+    (mkIf (cfg.dap.enable && cfg.lsp.enable && !elem "haskell-tools" cfg.lsp.servers) {
+      warnings = [
+        (
+          "You appear to have enabled vim.languages.haskell.dap, which implicitly "
+          + "causes haskell-tools-nvim plugin to be added. Make sure you also add "
+          + "'haskell-tools' server to vim.languages.haskell.lsp.servers"
+        )
+      ];
+    })
+
+    (mkIf (cfg.dap.enable || (cfg.lsp.enable && elem "haskell-tools" cfg.lsp.servers)) {
       vim = {
         startPlugins = ["haskell-tools-nvim"];
         luaConfigRC.haskell-tools-nvim =
@@ -113,7 +137,6 @@ in {
                   enable = true,
                 },
               },
-              hls = ${toLuaObject servers.hls},
             ''}
             ${optionalString cfg.dap.enable ''
               dap = {