Add RuboCop built-in launguage server for linting Ruby code

RuboCop is a Ruby static code analyzer (a.k.a. linter) and code formatter:
https://github.com/rubocop/rubocop

RuboCop provides built-in language server, as detailed here:
https://docs.rubocop.org/rubocop/usage/lsp.html.

This PR introduces a client for this server.

CHANGELOG.org

@@ -84,6 +84,7 @@
   * Add AWK language server support.
   * Add support for ~scala-ts-mode~.
   * Drop support for emacs 26.3
+  * Add [https://github.com/rubocop/rubocop][RuboCop built-in language server]] for linting and formatting Ruby code.
 ** Release 8.0.0
   * Add ~lsp-clients-angular-node-get-prefix-command~ to get the Angular server from another location which is still has ~/lib/node_modules~ in it.
   * Set ~lsp-clients-angular-language-server-command~ after the first connection to speed up subsequent connections.

clients/lsp-rubocop.el

@@ -0,0 +1,66 @@
+;;; lsp-rubocop.el --- lsp-mode for RuboCop  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2023  Koichi Ito
+
+;; Author: Koichi Ito <[email protected]>
+;; Keywords: lsp, ruby, languages
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; LSP client for RuboCop which is a Ruby static code analyzer (a.k.a. linter)
+;; and code formatter.
+
+;;; Code:
+
+(require 'lsp-mode)
+
+(defgroup lsp-rubocop nil
+  "LSP support for RuboCop, using the RuboCop built-in language server."
+  :group 'lsp-mode
+  :link '(url-link "https://github.com/rubocop/rubocop")
+  :package-version '(lsp-mode . "8.0.1"))
+
+(defcustom lsp-rubocop-use-bundler nil
+  "Run RuboCop using Bundler."
+  :type 'boolean
+  :safe #'booleanp
+  :group 'lsp-rubocop
+  :package-version '(lsp-mode . "8.0.1"))
+
+(defcustom lsp-rubocop-server-path nil
+  "Path of the RuboCop built-in language server executable.
+If specified, `lsp-rubocop-use-bundler' is ignored."
+  :type 'file
+  :group 'lsp-rubocop
+  :package-version '(lsp-mode . "8.0.1"))
+
+(defun lsp-rubocop--build-command ()
+  "Build a command to start the RuboCop built-in language server."
+  (append
+   (if (and lsp-rubocop-use-bundler (not lsp-rubocop-server-path)) '("bundle" "exec"))
+   (list (or lsp-rubocop-server-path "rubocop") "--lsp")))
+
+(lsp-register-client
+ (make-lsp-client
+  :new-connection (lsp-stdio-connection #'lsp-rubocop--build-command)
+  :activation-fn (lsp-activate-on "ruby")
+  :priority -1
+  :server-id 'rubocop-ls))
+
+(lsp-consistency-check lsp-rubocop)
+
+(provide 'lsp-rubocop)
+;;; lsp-rubocop.el ends here

docs/lsp-clients.json

@@ -732,6 +732,15 @@
     "installation": "npm i -g remark-language-server",
     "debugger": "Not available"
   },
+  {
+    "name": "robocop",
+    "full-name": "Ruby (RuboCop)",
+    "server-name": "rubocop",
+    "server-url": "https://github.com/rubocop/rubocop",
+    "installation-url": "https://docs.rubocop.org/rubocop/installation.html",
+    "installation": "gem install rubocop",
+    "debugger": "Not available"
+  },
   {
     "name": "robot",
     "full-name": "robot framework",

lsp-mode.el

@@ -183,8 +183,8 @@ As defined by the Language Server Protocol 3.16."
      lsp-lua lsp-markdown lsp-marksman lsp-mint lsp-nginx lsp-nim lsp-nix lsp-magik
      lsp-metals lsp-mssql lsp-ocaml lsp-openscad lsp-pascal lsp-perl lsp-perlnavigator
      lsp-pls lsp-php lsp-pwsh lsp-pyls lsp-pylsp lsp-pyright lsp-python-ms lsp-purescript
-     lsp-r lsp-racket lsp-remark lsp-ruff-lsp lsp-rf lsp-rust lsp-semgrep lsp-shader lsp-solargraph
-     lsp-sorbet lsp-sourcekit lsp-sonarlint lsp-tailwindcss lsp-tex lsp-terraform
+     lsp-r lsp-racket lsp-remark lsp-ruff-lsp lsp-rf lsp-rubocop lsp-rust lsp-semgrep lsp-shader
+     lsp-solargraph lsp-sorbet lsp-sourcekit lsp-sonarlint lsp-tailwindcss lsp-tex lsp-terraform
      lsp-toml lsp-ttcn3 lsp-typeprof lsp-v lsp-vala lsp-verilog lsp-vetur lsp-volar
      lsp-vhdl lsp-vimscript lsp-xml lsp-yaml lsp-ruby-lsp lsp-ruby-syntax-tree
      lsp-sqls lsp-svelte lsp-steep lsp-tilt lsp-zig)

mkdocs.yml

@@ -126,6 +126,7 @@ nav:
     - R: page/lsp-r.md
     - Racket (jeapostrophe): page/lsp-racket-langserver.md
     - Racket (Theia): page/lsp-racket-language-server.md
+    - Ruby (RuboCop): page/lsp-rubocop.md
     - Ruby (ruby-lsp): page/lsp-ruby-lsp.md
     - Ruby (Solargraph): page/lsp-solargraph.md
     - Ruby (Sorbet): page/lsp-sorbet.md