Modernize lsp-mode integration

* switch the company-backend used by lsp-mode from company-lsp to
company-capf (said to provide better performance and allows us to remove
the dependency on company-lsp)

* when available (on recent builds of Emacs 27+), lsp-mode buffers will
now use a larger than default value of `read-process-output-max`.
According to the lsp-mode performance guide, this can also significantly
improve lsp-mode performance

* flycheck support recently moved into lsp proper; with this commit,
the lsp module follows suit and prefers lsp-flycheck over
lsp-ui-flycheck

* if the new module flag `+no-peek` is set, doom-emacs will now use the xref
backend for reference and definition lookup instead of the lsp-ui-peek-*
backend offered by lsp-ui-mode

docs/modules.org

@@ -162,7 +162,7 @@ Small modules that give Emacs access to external tools & services.
 + gist - TODO
 + [[file:../modules/tools/lookup/README.org][lookup]] =+dictionary +docsets= - Universal jump-to & documentation lookup
   backend
-+ [[file:../modules/tools/lsp/README.org][lsp]] - TODO
++ [[file:../modules/tools/lsp/README.org][lsp]] =+peek= - TODO
 + macos - TODO
 + magit - TODO
 + make - TODO

modules/tools/lsp/README.org

@@ -52,12 +52,11 @@ As of this writing, this is the state of LSP support in Doom Emacs:
 | [[../../lang/web/README.org][:lang web]]        | web-mode, css-mode, scss-mode, sass-mode, less-css-mode | vscode-css-languageserver-bin, vscode-html-languageserver-bin |
 
 ** Module Flags
-This module provides no flags.
++ =+peek= Enables the =lsp-ui-peek= navigation frontend provided by the =lsp-ui= package.
 
 ** Plugins
 + [[https://github.com/emacs-lsp/lsp-mode][lsp-mode]]
 + [[https://github.com/emacs-lsp/lsp-ui][lsp-ui]]
-+ [[https://github.com/tigersoldier/company-lsp][company-lsp]]*
 
 * Prerequisites
 This module has no direct prerequisites, but major-modes require you to install

modules/tools/lsp/config.el

@@ -1,11 +1,20 @@
 ;;; tools/lsp/config.el -*- lexical-binding: t; -*-
 
 (defvar +lsp-company-backend 'company-lsp
-  "What backend to prepend to `company-backends' when `lsp-mode' is active.
+  "What backend to use for lsp-driven autocompletion, unless
+overridden by `+lsp-capf-blacklist'.
 
-This can be a single company backend or a list thereof. It can be anything
+While `company-capf' does not require the `company-lsp' package
-`company-backends' will accept.")
+and should offer better performance, it has been integrated into
+lsp only recently and as of 02/25/2020 is known to cause issues
+with some language servers. If you wish to use `company-capf' in
+general but fall back to `company-lsp' for specific language
+servers, set `+lsp-company-backend' to `company-capf' and add the
+excluded servers' identifiers to `+lsp-capf-blacklist'.")
 
+(defvar +lsp-capf-blacklist '(ts-ls gopls)
+  "Language servers listed here will always use the `company-lsp' backend,
+irrespective of what `+lsp-company-backend' is set to.")
 
 ;;
 ;;; Packages
@@ -20,6 +29,42 @@ This can be a single company backend or a list thereof. It can be anything
   ;; Auto-kill LSP server once you've killed the last buffer associated with its
   ;; project.
   (setq lsp-keep-workspace-alive nil)
+  (add-hook! 'lsp-mode-hook
+    (defun +lsp-init-company-h ()
+      (if (not (bound-and-true-p company-mode))
+          (add-hook 'company-mode-hook #'+lsp-init-company-h t t)
+        (let ((preferred-backend +lsp-company-backend))
+          (lsp-foreach-workspace
+           (when (memq (lsp--client-server-id (lsp--workspace-client lsp--cur-workspace))
+                       +lsp-capf-blacklist)
+             (setq preferred-backend 'company-lsp)))
+          (if (eq 'company-capf preferred-backend)
+              ;; use capf backend
+              (progn
+                (setq-local lsp-enable-completion-at-point t)
+                (setq-local lsp-prefer-capf t)
+                (setq-local company-backends
+                            (cons 'company-capf (remq 'company-capf company-backends))))
+            ;; use company-lsp backend (may need to be loaded first)
+            (require 'company-lsp)
+            (setq-local lsp-enable-completion-at-point nil)
+            (setq-local lsp-prefer-capf nil)
+            (setq-local company-backends
+                        (cons 'company-lsp (remq 'company-capf company-backends)))
+            (setq-default company-lsp-cache-candidates 'auto))
+          (remove-hook 'company-mode-hook #'+lsp-init-company-h t))))
+    (defun +lsp-init-flycheck-or-flymake-h ()
+      "Set up flycheck-mode or flymake-mode, depending on `lsp-diagnostic-package'."
+      (cond ((eq :none lsp-diagnostic-package))
+            ((or (eq :flymake lsp-diagnostic-package)
+                 (eq t lsp-diagnostic-package))
+             (lsp--flymake-setup))
+            ((require 'flycheck nil t)
+             (let ((old-checker flycheck-checker))
+               (lsp-flycheck-enable t)
+               (when old-checker
+                 (setq-local flycheck-checker old-checker)
+                 (kill-local-variable 'flycheck-check-syntax-automatically)))))))
 
   ;; For `lsp-clients'
   (setq lsp-server-install-dir (concat doom-etc-dir "lsp/")
@@ -79,7 +124,7 @@ modules.
 
 Also see:
 + `+lsp-init-company-h' (on `lsp-mode-hook')
-+ `+lsp-init-ui-flycheck-or-flymake-h' (on `lsp-ui-mode-hook')
++ `+lsp-init-flycheck-or-flymake-h' (on `lsp-mode-hook')
 
 This also logs the resolved project root, if found, so we know where we are."
     :override #'lsp
@@ -92,6 +137,10 @@ This also logs the resolved project root, if found, so we know where we are."
               (lsp--try-project-root-workspaces
                (equal arg '(4))
                (and arg (not (equal arg 1))))))
+         ;; read-process-output-max is only available on recent
+         ;; development builds of Emacs 27 and above
+         (when (boundp 'read-process-output-max)
+           (setq-local read-process-output-max (* 1024 1024)))
          (prog1 (lsp-mode 1)
            (setq-local lsp-buffer-uri (lsp--buffer-uri))
            ;; Announce what project root we're using, for diagnostic purposes
@@ -110,24 +159,9 @@ This also logs the resolved project root, if found, so we know where we are."
 
 (use-package! lsp-ui
   :hook (lsp-mode . lsp-ui-mode)
-  :init
-  (add-hook! 'lsp-ui-mode-hook
-    (defun +lsp-init-ui-flycheck-or-flymake-h ()
-      "Sets up flymake-mode or flycheck-mode, depending on `lsp-prefer-flymake'."
-      (cond ((eq :none lsp-prefer-flymake))
-            (lsp-prefer-flymake
-             (lsp--flymake-setup))
-            ((require 'flycheck nil t)
-             (require 'lsp-ui-flycheck)
-             (let ((old-checker flycheck-checker))
-               (lsp-ui-flycheck-enable t)
-               (when old-checker
-                 (setq-local flycheck-checker old-checker)
-                 (kill-local-variable 'flycheck-check-syntax-automatically)))))))
 
   :config
-  (setq lsp-prefer-flymake nil
+  (setq lsp-ui-doc-max-height 8
-        lsp-ui-doc-max-height 8
         lsp-ui-doc-max-width 35
         lsp-ui-sideline-ignore-duplicate t
         ;; lsp-ui-doc is redundant with and more invasive than
@@ -138,27 +172,10 @@ This also logs the resolved project root, if found, so we know where we are."
         ;; errors flash briefly and then disappear).
         lsp-ui-sideline-show-hover nil)
 
-  (set-lookup-handlers! 'lsp-ui-mode :async t
+  (when (featurep! +peek)
-    :definition 'lsp-ui-peek-find-definitions
+    (set-lookup-handlers! 'lsp-ui-mode :async t
-    :references 'lsp-ui-peek-find-references))
+      :definition 'lsp-ui-peek-find-definitions
-
+      :references 'lsp-ui-peek-find-references)))
-
-(use-package! company-lsp
-  :when (featurep! :completion company)
-  :defer t
-  :init
-  ;; Make sure that `company-capf' is disabled since it is incompatible with
-  ;; `company-lsp' (see lsp-mode#884)
-  (add-hook! 'lsp-mode-hook
-    (defun +lsp-init-company-h ()
-      (if (not (bound-and-true-p company-mode))
-          (add-hook 'company-mode-hook #'+lsp-init-company-h t t)
-        (setq-local company-backends
-                    (cons +lsp-company-backend
-                          (remq 'company-capf company-backends)))
-        (remove-hook 'company-mode-hook #'+lsp-init-company-h t))))
-  :config
-  (setq company-lsp-cache-candidates 'auto)) ;; cache candidates for better performance
 
 
 (use-package! helm-lsp

modules/tools/lsp/packages.el

@@ -1,8 +1,8 @@
 ;; -*- no-byte-compile: t; -*-
 ;;; tools/lsp/packages.el
 
-(package! lsp-mode :pin "2fc0963a50")
+(package! lsp-mode :pin "fc812bea1f")
-(package! lsp-ui :pin "e8200e3b72")
+(package! lsp-ui :pin "da9788b427")
 (when (featurep! :completion company)
   (package! company-lsp :pin "f921ffa0cd"))
 (when (featurep! :completion ivy)