[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/lang/cc/config.el

@@ -236,9 +236,45 @@ If rtags or rdm aren't available, fail silently instead of throwing a breaking e
       (setq-local company-lsp-cache-candidates nil)
       (lsp!))))
 
+(when (and (featurep! +lsp) (featurep! :tools lsp +eglot))
+  ;; TODO : test this value
+  ;; IS-MAC custom configuration
+  (when IS-MAC
+    (add-to-list 'eglot-workspace-configuration
+                 ((:ccls . ((:clang . ,(list :extraArgs ["-isystem/Library/Developer/CommandLineTools/usr/include/c++/v1"
+                                      "-isystem/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include"
+                                      "-isystem/usr/local/include"]
+                          :resourceDir (string-trim (shell-command-to-string "clang -print-resource-dir")))))))))
+  ;; Eglot specific helper, courtesy of MaskRay
+  (defun eglot-ccls-inheritance-hierarchy (&optional derived)
+  "Show inheritance hierarchy for the thing at point.
+If DERIVED is non-nil (interactively, with prefix argument), show
+the children of class at point."
+  (interactive "P")
+  (if-let* ((res (jsonrpc-request
+                  (eglot--current-server-or-lose)
+                  :$ccls/inheritance
+                  (append (eglot--TextDocumentPositionParams)
+                          `(:derived ,(if derived t :json-false))
+                          '(:levels 100) '(:hierarchy t))))
+            (tree (list (cons 0 res))))
+      (with-help-window "*ccls inheritance*"
+        (with-current-buffer standard-output
+          (while tree
+            (pcase-let ((`(,depth . ,node) (pop tree)))
+              (cl-destructuring-bind (&key uri range) (plist-get node :location)
+                (insert (make-string depth ?\ ) (plist-get node :name) "\n")
+                (make-text-button (+ (point-at-bol 0) depth) (point-at-eol 0)
+                                  'action (lambda (_arg)
+                                            (interactive)
+                                            (find-file (eglot--uri-to-path uri))
+                                            (goto-char (car (eglot--range-region range)))))
+                (cl-loop for child across (plist-get node :children)
+                         do (push (cons (1+ depth) child) tree)))))))
+    (eglot--error "Hierarchy unavailable"))))
 
 (use-package! ccls
-  :when (featurep! +lsp)
+  :when (and (featurep! +lsp) (not (featurep! :tools lsp +eglot)))
   :after lsp
   :init
   (after! projectile

modules/lang/cc/packages.el

@@ -17,7 +17,9 @@
       :pin "404cd0694a")))
 
 (if (featurep! +lsp)
-    (package! ccls :pin "17ec7bb4cf")
+    (unless (featurep! :tools lsp +eglot)
+      ;; ccls package is necessary only for lsp-mode.
+      (package! ccls :pin "17ec7bb4cf"))
   (when (package! irony :pin "5f75fc0c92")
     (package! irony-eldoc :pin "0df5831eaa")
     (when (featurep! :checkers syntax)

modules/lang/haskell/packages.el

@@ -6,6 +6,6 @@
 (when (featurep! +dante)
   (package! dante :pin "4955bc7363")
   (package! attrap :pin "4cf3e4a162"))
-(when (or (featurep! +lsp)
+(when (or (and (featurep! +lsp) (not (featurep! :tools lsp +eglot)))
           (featurep! +ghcide))
   (package! lsp-haskell :pin "582fa27c88"))

modules/lang/python/config.el

@@ -22,7 +22,10 @@ called.")
         python-indent-guess-indent-offset-verbose nil)
 
   (when (featurep! +lsp)
-    (add-hook 'python-mode-local-vars-hook #'lsp!))
+    (add-hook 'python-mode-local-vars-hook #'lsp!)
+    ;; Use "mspyls" in eglot if in PATH
+    (when (executable-find "Microsoft.Python.LanguageServer")
+      (set-eglot-client! 'python-mode '("Microsoft.Python.LanguageServer"))))
   :config
   (set-repl-handler! 'python-mode #'+python/open-repl :persist t)
   (set-docsets! 'python-mode "Python 3" "NumPy" "SciPy")
@@ -98,6 +101,7 @@ called.")
       "Enable `anaconda-mode' if `lsp-mode' is absent and
 `python-shell-interpreter' is present."
       (unless (or (bound-and-true-p lsp-mode)
+                  (bound-and-true-p eglot--managed-mode)
                   (bound-and-true-p lsp--buffer-deferred)
                   (not (executable-find python-shell-interpreter)))
         (anaconda-mode +1))))
@@ -286,7 +290,7 @@ called.")
 
 
 (use-package! lsp-python-ms
-  :when (featurep! +lsp)
+  :when (and (featurep! +lsp) (not (featurep! :tools lsp +eglot)))
   :after lsp-clients
   :preface
   (after! python

modules/lang/python/packages.el

@@ -9,7 +9,7 @@
     (package! flycheck-cython :pin "ecc4454d35")))
 
 ;; LSP
-(when (featurep! +lsp)
+(when (and (featurep! +lsp) (not (featurep! :tools lsp +eglot)))
   (package! lsp-python-ms :pin "5d0c799099"))
 
 ;; Programming environment

modules/lang/rust/config.el

@@ -27,6 +27,11 @@
     (after! rustic-flycheck
       (add-to-list 'flycheck-checkers 'rustic-clippy)))
 
+  (when (featurep! +lsp)
+    (if (featurep! :tools lsp +eglot)
+        (setq rustic-lsp-client 'eglot)
+      (setq rustic-lsp-client 'lsp-mode)))
+
   (map! :map rustic-mode-map
         :localleader
         (:prefix ("b" . "build")