tools/lsp: reduce lsp's self-configuring eagerness

The original `lsp' initializes too much, too quickly. Things like
flycheck, company, and yasnippet. Doom's modules already handle these
just fine, so we advice it to leave it to us to handle. I intentionally
avoid disabling lsp-auto-configure because doing so is much more
destructive than I'd like.

This update prevents lsp-ui-mode from being auto-enabled on lsp-mode.
You can now (remove-hook 'lsp-mode-hook #'lsp-ui-mode) to disable
lsp-ui.

This update also adds these two hooks:

+ +lsp|init-company (on `lsp-mode-hook')
+ +lsp|init-ui-flycheck-or-flymake (on `lsp-ui-mode-hook')

modules/tools/lsp/autoload.el

@@ -1,4 +1,23 @@
 ;;; feature/lsp/autoload.el -*- lexical-binding: t; -*-
 
 ;;;###autodef
-(defalias 'lsp! #'lsp)
+(defun lsp! (&optional arg)
+  "Enable `lsp-mode' in the current buffer.
+
+Meant to be a lighter alternative to `lsp', which is too eager about
+initializing lsp-ui-mode, company, yasnippet and flycheck. Instead, these have
+been moved out to their respective modules, or these hooks:
+
++ `+lsp|init-company' (on `lsp-mode-hook')
++ `+lsp|init-ui-flycheck-or-flymake' (on `lsp-ui-mode-hook')"
+  (when lsp-auto-configure
+    (require 'lsp-clients))
+  (when (and (buffer-file-name)
+             (setq-local lsp--buffer-workspaces
+                         (or (lsp--try-open-in-library-workspace)
+                             (lsp--try-project-root-workspaces (equal arg '(4))
+                                                               (and arg (not (equal arg 1)))))))
+    (lsp-mode 1)
+    (lsp--info "Connected to %s."
+               (apply 'concat (--map (format "[%s]" (lsp--workspace-print it))
+                                     lsp--buffer-workspaces)))))

modules/tools/lsp/config.el

@@ -9,12 +9,27 @@
   (set-lookup-handlers! 'lsp-mode :async t
     :documentation 'lsp-describe-thing-at-point)
 
+  ;; The original `lsp' initializes too much, too quickly. Things like flycheck,
+  ;; company, and yasnippet. Doom's modules already handle these just fine, so
+  ;; leave it to us.
+  (advice-add #'lsp :override #'lsp!)
+
   ;; Don't prompt to restart LSP servers while quitting Emacs
   (add-hook! 'kill-emacs-hook (setq lsp-restart 'ignore)))
 
 
 (def-package! lsp-ui
   :hook (lsp-mode . lsp-ui-mode)
+  :init
+  (defun +lsp|init-ui-flycheck-or-flymake ()
+    "Sets up flymake-mode or flycheck-mode, depending on `lsp-prefer-flymake'."
+    (unless (eq :none lsp-prefer-flymake)
+      (if (and (not (version< emacs-version "26.1"))
+               lsp-prefer-flymake)
+          (lsp--flymake-setup))
+      (require 'lsp-ui-flycheck)
+      (lsp-ui-flycheck-enable t)))
+  (add-hook 'lsp-ui-mode-hook #'+lsp|init-ui-flycheck-or-flymake)
   :config
   (setq lsp-prefer-flymake nil
         lsp-ui-doc-max-height 8
@@ -33,4 +48,8 @@
   :when (featurep! :completion company)
   :after lsp-mode
   :config
-  (set-company-backend! 'lsp-mode 'company-lsp))
+  ;; Make sure that `company-capf' is disabled since it is incompatible with
+  ;; `company-lsp' (see lsp-mode#884)
+  (setq-hook! 'lsp-mode-hook company-backends
+              (cons 'company-lsp
+                    (remq 'company-capf company-backends))))