[eglot] Add support for eglot lsp client in emacs

- Update README
- Add eglot-specifics to cc, rs, py, hs
  removing unused lsp-mode packages when eglot is active
- Add eglot-specific bindings
- Add doctor warnings for debugger +lsp and +peek
- Add eglot-backed lookup-handlers
- Add flycheck checker using eglot for :checkers
  syntax users (using flycheck/flycheck#1676 and
  flycheck/flycheck#1592 discussion).
  This implementation is based on @marsam code, and uses recent
  Flycheck development in order to make the code smaller and
  easier to maintain.

modules/tools/lsp/autoload/common.el

@@ -0,0 +1,9 @@
+;;; tools/lsp/autoload/common.el -*- lexical-binding: t; -*-
+
+;;;###autodef
+(defun lsp! ()
+  "Dispatch to call the currently used lsp client entrypoint"
+  (interactive)
+  (if (featurep! +eglot)
+      (eglot-ensure)
+    (lsp-deferred)))

modules/tools/lsp/autoload/eglot.el

@@ -0,0 +1,19 @@
+;;; tools/lsp/autoload/eglot.el -*- lexical-binding: t; -*-
+;;;###if (featurep! +eglot)
+
+;;;###autodef
+(defun set-eglot-client! (mode server-call)
+  "Add SERVER-CALL list as a possible lsp server for given major MODE.
+
+Example : (set-eglot-client! 'python-mode `(,(concat doom-etc-dir \"lsp/mspyls/Microsoft.Python.LanguageServer\")))"
+  (when (featurep! +eglot)
+    (add-to-list 'eglot-server-programs `(,mode . ,server-call))))
+
+;;;###autoload
+(defun +eglot/documentation-lookup-handler ()
+  "Documentation lookup handler using eglot :document/hover handler.
+
+Mostly a rewrite of `eglot-help-at-point', which should be used interactively."
+  (interactive)
+  (eglot-help-at-point)
+  (display-buffer eglot--help-buffer))

modules/tools/lsp/autoload/lsp-mode.el

@@ -0,0 +1,51 @@
+;;; tools/lsp/autoload/lsp-mode.el -*- lexical-binding: t; -*-
+;;;###if (not (featurep! +eglot))
+
+;;;###autodef
+(defun set-lsp-priority! (client priority)
+  "Change the PRIORITY of lsp CLIENT."
+  (require 'lsp-mode)
+  (if-let (client (gethash client lsp-clients))
+      (setf (lsp--client-priority client)
+            priority)
+    (error "No LSP client named %S" client)))
+
+;;;###autoload
+(defun +lsp/uninstall-server (dir)
+  "Delete a LSP server from `lsp-server-install-dir'."
+  (interactive
+   (list (read-directory-name "Uninstall LSP server: " lsp-server-install-dir nil t)))
+  (unless (file-directory-p dir)
+    (user-error "Couldn't find %S directory" dir))
+  (delete-directory dir 'recursive)
+  (message "Uninstalled %S" (file-name-nondirectory dir)))
+
+;;;###autoload
+(defun +lsp/switch-client (client)
+  "Switch to another LSP server."
+  (interactive
+   (progn
+     (require 'lsp-mode)
+     (list (completing-read
+            "Select server: "
+            (or (mapcar #'lsp--client-server-id (lsp--find-clients))
+                (user-error "No available LSP clients for %S" major-mode))))))
+  (require 'lsp-mode)
+  (let* ((client (if (symbolp client) client (intern client)))
+         (match (car (lsp--filter-clients (lambda (c) (eq (lsp--client-server-id c) client)))))
+         (workspaces (lsp-workspaces)))
+    (unless match
+      (user-error "Couldn't find an LSP client named %S" client))
+    (let ((old-priority (lsp--client-priority match)))
+      (setf (lsp--client-priority match) 9999)
+      (unwind-protect
+          (if workspaces
+              (lsp-workspace-restart
+               (if (cdr workspaces)
+                   (lsp--completing-read "Select server: "
+                                         workspaces
+                                         'lsp--workspace-print
+                                         nil t)
+                 (car workspaces)))
+            (lsp-mode +1))
+        (setf (lsp--client-priority match) old-priority)))))