lsp: add support for several LSP clients (#111)

* nvim-lsp: Allow to pass settings to clients

Some clients (like rust-analyzer, nil_ls, ...) can take settings
specified in the setup function. This commit adds two fields for the
'mkLsp' function to handle this:

- extraOptions: define nix module options
- settings: A function that takes the corresponding lsp module config
  and formats it as a settings object compatible with the server.

* nvim-lsp: Add nil-ls (for Nix)

* nvim-lsp: Add bashls (for Bash)

* nvim-lsp: Add dartls, for dart

Co-authored-by: Pedro Alves <pta2002@users.noreply.github.com>

plugins/nvim-lsp/basic-servers.nix

@@ -1,4 +1,5 @@
 { pkgs, config, lib, ... }@args:
+with lib;
 let
   helpers = import ./helpers.nix args;
   servers = [
@@ -17,6 +18,97 @@ let
       description = "Enable cssls, for CSS";
       packages = [ pkgs.nodePackages.vscode-langservers-extracted ];
     }
+    {
+      name = "dartls";
+      description = "Enable dart language-server, for dart";
+      packages = [ pkgs.dart ];
+      extraOptions = {
+        analysisExcludedFolders = mkOption {
+          type = types.nullOr (types.listOf types.str);
+          default = null;
+          description = ''
+            An array of paths (absolute or relative to each workspace folder) that should be 
+            excluded from analysis.
+          '';
+        };
+        enableSdkFormatter = mkOption {
+          type = types.nullOr types.bool;
+          default = null;
+          description = ''
+            When set to false, prevents registration (or unregisters) the SDK formatter. When set 
+            to true or not supplied, will register/reregister the SDK formatter
+          '';
+        };
+        lineLength = mkOption {
+          type = types.nullOr types.int;
+          default = null;
+          description = ''
+            The number of characters the formatter should wrap code at. If unspecified, code will 
+            be wrapped at 80 characters.
+          '';
+        };
+        completeFunctionCalls = mkOption {
+          type = types.nullOr types.bool;
+          default = true;
+          description = ''
+            When set to true, completes functions/methods with their required parameters.
+          '';
+        };
+        showTodos = mkOption {
+          type = types.nullOr types.bool;
+          default = true;
+          description = ''
+            Whether to generate diagnostics for TODO comments. If unspecified, diagnostics will not 
+            be generated.
+          '';
+        };
+        renameFilesWithClasses = mkOption {
+          type = types.nullOr (types.enum [ "always" "prompt" ]);
+          default = null;
+          description = ''
+            When set to "always", will include edits to rename files when classes are renamed if the
+            filename matches the class name (but in snake_form). When set to "prompt", a prompt will
+            be shown on each class rename asking to confirm the file rename. Otherwise, files will
+            not be renamed. Renames are performed using LSP's ResourceOperation edits - that means
+            the rename is simply included in the resulting WorkspaceEdit and must be handled by the
+            client.
+          '';
+        };
+        enableSnippets = mkOption {
+          type = types.nullOr types.bool;
+          default = null;
+          description = ''
+            Whether to include code snippets (such as class, stful, switch) in code completion. When
+            unspecified, snippets will be included.
+          '';
+        };
+        updateImportsOnRename = mkOption {
+          type = types.nullOr types.bool;
+          default = null;
+          description = ''
+            Whether to update imports and other directives when files are renamed. When unspecified,
+            imports will be updated if the client supports willRenameFiles requests
+          '';
+        };
+        documentation = mkOption {
+          type = types.nullOr (types.enum [ "none" "summary" "full" ]);
+          default = null;
+          description = ''
+            The typekind of dartdocs to include in Hovers, Code Completion, Signature Help and other
+            similar requests. If not set, defaults to full
+          '';
+        };
+        includeDependenciesInWorkspaceSymbols = mkOption {
+          type = types.nullOr types.bool;
+          default = null;
+          description = ''
+            Whether to include symbols from dependencies and Dart/Flutter SDKs in Workspace Symbol 
+            results. If not set, defaults to true.
+          '';
+        };
+      };
+      settings = cfg: { dart = cfg; };
+    }
     {
       name = "denols";
       description = "Enable denols, for Deno";
@@ -52,6 +144,42 @@ let
       description = "Enable jsonls, for JSON";
       packages = [ pkgs.nodePackages.vscode-langservers-extracted ];
     }
+    {
+      name = "nil_ls";
+      description = "Enable nil, for Nix";
+      packages = [ pkgs.nil ];
+      extraOptions = {
+        formatting.command = mkOption {
+          type = types.nullOr (types.listOf types.str);
+          default = null;
+          description = ''
+            External formatter command (with arguments).
+            It should accepts file content in stdin and print the formatted code into stdout.
+          '';
+        };
+        diagnostics = {
+          ignored = mkOption {
+            type = types.listOf types.str;
+            default = [ ];
+            description = ''
+              Ignored diagnostic kinds.
+              The kind identifier is a snake_cased_string usually shown together
+              with the diagnostic message.
+            '';
+          };
+          excludedFiles = mkOption {
+            type = types.listOf types.str;
+            default = [ ];
+            description = ''
+              Files to exclude from showing diagnostics. Useful for generated files.
+              It accepts an array of paths. Relative paths are joint to the workspace root.
+              Glob patterns are currently not supported.
+            '';
+          };
+        };
+      };
+      settings = cfg: { nil = { inherit (cfg) formatting diagnostics; }; };
+    }
     {
       name = "pyright";
       description = "Enable pyright, for Python.";

plugins/nvim-lsp/helpers.nix

@@ -7,6 +7,8 @@
     , serverName ? name
     , packages ? [ pkgs.${name} ]
     , cmd ? null
+    , settings ? null
+    , extraOptions ? { }
     , ...
     }:
     # returns a module
@@ -19,7 +21,7 @@
         options = {
           plugins.lsp.servers.${name} = {
             enable = mkEnableOption description;
-          };
+          } // extraOptions;
         };
 
         config = mkIf cfg.enable {
@@ -29,6 +31,7 @@
             name = serverName;
             extraOptions = {
               inherit cmd;
+              settings = if settings != null then settings cfg else { };
             };
           }];
         };