Add lsp support for go

layers/+lang/go/README.org

@@ -7,6 +7,7 @@
   - [[#features][Features:]]
 - [[#install][Install]]
   - [[#pre-requisites][Pre-requisites]]
+  - [[#lsp-backend][LSP backend]]
   - [[#layer][Layer]]
 - [[#configuration][Configuration]]
   - [[#indentation][Indentation]]
@@ -32,6 +33,7 @@ This layer adds extensive support for go to Spacemacs.
 - Test generation with [[https://github.com/s-kostyaev/go-gen-test][go-gen-test]]
 - Get packages faster with [[https://github.com/haya14busa/gopkgs][gopkgs]]
 - Fill a structure with default values using the [[https://github.com/davidrjenni/reftools/tree/master/cmd/fillstruct][fillstruct]]
+- LSP backend
 
 * Install
 ** Pre-requisites
@@ -87,6 +89,32 @@ $PATH RET~).
 For best results, make sure that the =auto-completion= and =syntax-checking=
 layers are enabled as well.
 
+** LSP backend
+ To enable the LSP backend set the layer variable =go-backend=:
+
+#+BEGIN_SRC elisp
+(go :variables go-backend 'lsp)
+#+END_SRC
+
+You also need to install the Go Language Server:
+
+#+BEGIN_SRC sh
+  go get -u github.com/sourcegraph/go-langserver
+#+END_SRC
+
+Backend can be chosen on a per project basis using directory local variables
+(files named =.dir-locals.el= at the root of a project), an example to use the
+=default= backend:
+
+#+BEGIN_SRC elisp
+;;; Directory Local Variables
+;;; For more information see (info "(emacs) Directory Variables")
+
+((go-mode (go-backend . default)))
+#+END_SRC
+
+*Note:* you can easily add a directory local variable with ~SPC f v d~.
+
 ** Layer
 To use this configuration layer, add it to your =~/.spacemacs=. You will need to
 add =go= to the existing =dotspacemacs-configuration-layers= list in this

layers/+lang/go/config.el

@@ -13,6 +13,8 @@
 
 (spacemacs|define-jump-handlers go-mode godef-jump)
 
+(defvar go-backend 'default)
+
 (defvar go-use-gocheck-for-testing nil
   "If using gocheck for testing when running the tests -check.f will be used instead of -run to specify the test that will be ran. Gocheck is mandatory for testing suites.")
 

layers/+lang/go/funcs.el

@@ -14,6 +14,50 @@
   (when go-tab-width
     (setq-local tab-width go-tab-width)))
 
+(defun spacemacs//go-setup-backend ()
+  "Conditionally setup go backend"
+  (pcase go-backend
+    ('default (spacemacs//go-setup-backend-default))
+    ('lsp (spacemacs//go-setup-backend-lsp))))
+
+(defun spacemacs//go-setup-company ()
+  "Conditionally setup go company based on backend"
+  (pcase go-backend
+    ('default (spacemacs//go-setup-company-go))
+    ('lsp (spacemacs//go-setup-company-lsp))))
+
+(defun spacemacs//go-setup-backend-default ()
+  (company-go))
+
+(defun spacemacs//go-setup-company-go ()
+  (spacemacs|add-company-backends
+    :backends company-go
+    :modes go-mode
+    :variables company-go-show-annotation t
+    :append-hooks nil
+    :call-hooks t)
+  (company-mode))
+
+(defun spacemacs//go-setup-backend-lsp ()
+  "Setup lsp backend"
+  (if (configuration-layer/layer-used-p 'lsp)
+      (progn
+        (require 'lsp-go)
+        (lsp-go-enable))
+    (message "`lsp' layer is not installed, please add `lsp' layer to your dotfile.")))
+
+(defun spacemacs//go-setup-company-lsp ()
+  "Setup lsp auto-completion"
+  (if (configuration-layer/layer-used-p 'lsp)
+      (progn
+        (spacemacs|add-company-backends
+          :backends company-lsp
+          :modes go-mode
+          :append-hooks nil
+          :call-hooks t)
+        (company-mode))
+    (message "`lsp' layer is not installed, please add `lsp' layer to your dotfile.")))
+
 (defun spacemacs//go-enable-gometalinter ()
    "Enable `flycheck-gometalinter' and disable overlapping `flycheck' linters."
    (setq flycheck-disabled-checkers '(go-gofmt

layers/+lang/go/packages.el

@@ -11,6 +11,7 @@
 
 (setq go-packages
       '(
+        company
         (company-go :requires company)
         counsel-gtags
         flycheck
@@ -28,6 +29,10 @@
         go-rename
         go-tag
         godoctor
+        (lsp-go
+         :requires lsp-mode
+         :location (recipe :fetcher github
+                           :repo "emacs-lsp/lsp-go"))
         popwin
         ))
 
@@ -39,6 +44,13 @@
             :modes go-mode
             :variables company-go-show-annotation t)))
 
+(defun go/init-lsp-go ()
+  (use-package lsp-go
+    :commands lsp-go-enable))
+
+(defun go/post-init-company ()
+  (add-hook 'go-mode-local-vars-hook #'spacemacs//go-setup-company))
+
 (defun go/post-init-counsel-gtags ()
   (spacemacs/counsel-gtags-define-keys-for-mode 'go-mode))
 
@@ -108,7 +120,12 @@
     (progn
       ;; get go packages much faster
       (setq go-packages-function 'spacemacs/go-packages-gopkgs)
-      (add-hook 'go-mode-hook 'spacemacs//go-set-tab-width))
+      (add-hook 'go-mode-hook 'spacemacs//go-set-tab-width)
+      (add-hook 'go-mode-local-vars-hook
+                #'spacemacs//go-setup-backend)
+      (dolist (value '(lsp default))
+        (add-to-list 'safe-local-variable-values
+                     (cons 'go-backend value))))
     :config
     (progn
       (when go-format-before-save