lang/lua: update README & refactor

Mentioned in #4462

modules/lang/lua/README.org

@@ -39,19 +39,28 @@ This module has no dedicated maintainers.
 
 * Prerequisites
 ** Language Server Protocol servers
-Currently the servers supported depend on the =:tools lsp= flavor you are using
+LSP server support depends on which flavor of the =:tools lsp= module you have
+installed (Eglot or LSP-mode).
+
 *** LSP-mode
-This server is built in Java, so a ~java~ environment will be necessary
-+ [[https://github.com/EmmyLua/EmmyLua-LanguageServer][EmmyLua-LanguageServer]] must be installed and configured to use the
-  configuration provided by emacs-lsp.
+Three servers are supported, ordered from highest to lowest priority:
+
++ [[https://github.com/EmmyLua/EmmyLua-LanguageServer][EmmyLua-LanguageServer]] :: Must be in =~/.emacs.d/.local/etc/lsp/EmmyLua-LS-all.jar=. See ~lsp-clients-emmy-lua-jar-path~ variable to change this.
++ [[https://github.com/sumneko/lua-language-server][Sumneko language server]] (lua-language-server) :: Must be in
+  =~/.config/emacs/.local/etc/lsp/lua-language-server/=. See
+  ~lsp-clients-lua-language-server-bin~ variable to change this.
++ [[https://github.com/Alloyed/lua-lsp][lua-lsp]] :: Must be available in =~/.luarocks/bin/lua-lsp=. See
+  ~lsp-clients-lua-lsp-server-install-dir~ variable to change this.
 
 [[https://emacs-lsp.github.io/lsp-mode/page/lsp-emmy-lua/][LSP-mode documentation]] has more information about setting up the server and the
-configuration variables correctly (use a bare ~(setq
-lsp-clients-emmy-lua-java-path value)~ in your =config.el=)
+configuration variables correctly.
+
 *** Eglot
-This server is built in Lua, so a =lua= environment will be necessary
-+ [[https://github.com/sumneko/lua-language-server][lua-language-server]] must be installed and built locally, with =+lua-lsp-dir=
-  variable pointing to the root of the repository
+Eglot currently only supports one of the above servers out of the box:
+
++ [[https://github.com/sumneko/lua-language-server][Sumneko language server]] (lua-language-server) :: Must be in
+  =~/.config/emacs/.local/etc/lsp/lua-language-server/=. See
+  ~+lua-lsp-dir~ variable to change this.
 
 * TODO Features
 # An in-depth list of features, how to use them, and their dependencies.

modules/lang/lua/config.el

@@ -1,11 +1,5 @@
 ;;; lang/lua/config.el -*- lexical-binding: t; -*-
 
-(defvar +lua-lsp-dir (concat doom-etc-dir "lsp/lua-language-server/")
-  "Absolute path to the directory of sumneko's lua-language-server.
-
-This directory MUST contain the 'main.lua' file and be the in-source build of
-lua-language-server.")
-
 ;; sp's default rules are obnoxious, so disable them
 (provide 'smartparens-lua)
 
@@ -25,27 +19,29 @@ lua-language-server.")
   (set-company-backend! 'lua-mode '(company-lua company-yasnippet))
 
   (when (featurep! +lsp)
-    (defun +lua-generate-lsp-server-command ()
-      ;; The absolute path to lua-language-server binary is necessary because
-      ;; the bundled dependencies aren't found otherwise. The only reason this
-      ;; is a function is to dynamically change when/if `+lua-lsp-dir' does
-      (list (doom-path +lua-lsp-dir
-                       (cond (IS-MAC     "bin/macOS")
-                             (IS-LINUX   "bin/Linux")
-                             (IS-WINDOWS "bin/Windows"))
-                       "lua-language-server")
-            "-E" "-e" "LANG=en"
-            (doom-path +lua-lsp-dir "main.lua")))
+    (add-hook 'lua-mode-local-vars-hook #'lsp!)
 
-    (if (featurep! :tools lsp +eglot)
-        (set-eglot-client! 'lua-mode (+lua-generate-lsp-server-command))
-      (after! lsp-mode
-        (lsp-register-client
-         (make-lsp-client :new-connection (lsp-stdio-connection '+lua-generate-lsp-server-command)
-                          :major-modes '(lua-mode)
-                          :priority -1
-                          :server-id 'lua-langserver))))
-    (add-hook 'lua-mode-local-vars-hook #'lsp!)))
+    (when (featurep! :tools lsp +eglot)
+      (defvar +lua-lsp-dir (concat doom-etc-dir "lsp/lua-language-server/")
+        "Absolute path to the directory of sumneko's lua-language-server.
+
+This directory MUST contain the 'main.lua' file and be the in-source build of
+lua-language-server.")
+
+      (defun +lua-generate-lsp-server-command ()
+        ;; The absolute path to lua-language-server binary is necessary because
+        ;; the bundled dependencies aren't found otherwise. The only reason this
+        ;; is a function is to dynamically change when/if `+lua-lsp-dir' does
+        (list (or (executable-find "lua-language-server")
+                  (doom-path +lua-lsp-dir
+                             (cond (IS-MAC     "bin/macOS")
+                                   (IS-LINUX   "bin/Linux")
+                                   (IS-WINDOWS "bin/Windows"))
+                             "lua-language-server"))
+              "-E" "-e" "LANG=en"
+              (doom-path +lua-lsp-dir "main.lua")))
+
+      (set-eglot-client! 'lua-mode (+lua-generate-lsp-server-command)))))
 
 
 (use-package! moonscript