Update of prelude-go to replace gocode backend with lsp-mode and gopls (#1363)

.gitignore

@@ -30,3 +30,4 @@ transient/
 var/
 .cache/
 .lsp-session*
+gotools/

doc/modules/go.md

@@ -0,0 +1,87 @@
+# Prelude Go
+
+This module builds on top of the shared [Programming](programming.md)
+module, as well as the [Prelude-LSP](lsp.md) module.
+
+The following keybindings are set by default, which are not present in
+each mode's default bindings:
+
+* <kbd>C-c a</kbd> (`go-test-current-project`)
+* <kbd>C-c m</kbd> (`go-test-current-file`)
+* <kbd>C-c .</kbd> (`go-test-current-test`)
+* <kbd>C-c b</kbd> (`go-run`)
+* <kbd>C-h f</kbd> (`godoc-at-point`)
+
+Run <kbd>C-h m</kbd> for all the key bindings and other documentation.
+
+There are two ways to manage projects in Go: `$GOPATH` and with Go
+modules. Modules are the newer, recommended method. Read [Using Go
+Modules](https://go.dev/blog/using-go-modules) to learn about this, if
+you are unfamiliar with the subject. Many of the tools used by Prelude
+Go may provide functions that are broken with modules. There is
+usually another function that will work properly; when in doubt, use a
+function provided by `lsp-mode` which is documented below.
+
+Generics were added to Go in 1.18. `gopls`, the backend for `lsp-mode`
+setup herein, supports generics as long as `gopls` itself was built
+with 1.18+. Other minor modes may not support generics yet.
+
+## Go Mode
+
+`prelude-go` builds on several useful Go tools, and establishes sensible
+defaults. The major mode is `go-mode`. Documentation is available at [github.com/dominikh/go-mode.el](https://github.com/dominikh/go-mode.el)
+
+## Go Projectile
+
+[Projectile](https://github.com/bbatsov/projectile) integration is
+provided by [go-projectile](https://github.com/dougm/go-projectile).
+
+This provides:
+
+* Projectile integration
+* Switching GOPATH if desired per project (customizable via
+  `customize`)
+* Ability to download all commonly used `go` tools via <kbd>M-x
+  go-projectile-install-tools</kbd> and update them via <kbd>M-x
+  go-projectile-update-tools</kbd>
+* Very basic refactoring via `go-projectile-rewrite` (uses `gofmt -r`)
+* Support for `go get` and `go get -u` via `go-projectile-get` and
+  `go-projectile-update`.
+
+See its documentation for details.
+
+## LSP Mode and LSP UI
+
+[LSP](https://microsoft.github.io/language-server-protocol/) (Language
+Server Protocol) is a protocol that allows editors to use an external
+"language server" to provide features like autocompletion,
+documentation, and code navigation rather than implementing these
+features separately in each editor. Emacs supports LSP via
+`lsp-mode`. The language server used is
+[gopls](https://github.com/golang/tools/tree/master/gopls).
+
+To install `gopls`, change to a directory outside of `$GOPATH` or any
+module (e.g., `/tmp`) and execute:
+
+```
+go install golang.org/x/tools/gopls@latest
+```
+
+Ensure that `gopls` is in your `$PATH`.
+
+Excellent documentation for `lsp-mode` and `lsp-ui` are provided at [emacs-lsp.github.io/lsp-mode/](https://emacs-lsp.github.io/lsp-mode/)
+
+If a feature, such as documentation, refactoring, indenting, etc. is
+provided by `lsp`, you should use it instead of calling to another
+tool. `gopls` is the officially maintained tool that supercedes
+functionality in other tools, like `gocode`, and works properly with
+modules and generics.
+
+Company support is automatically added that works with `lsp`.
+
+## GoTest
+
+[gotest](https://github.com/nlamirault/gotest.el) is also provided
+while editing Go files in order to run tests more easily. The bindings
+provided by `prelude-go` are listed at the top because `gotest` does
+not set any.

modules/prelude-go.el

@@ -29,11 +29,13 @@
 ;;; Code:
 
 (require 'prelude-programming)
+(require 'prelude-lsp)
 
 (prelude-require-packages '(go-mode
-                            company-go
-                            go-eldoc
                             go-projectile
+                            lsp-mode
+                            lsp-ui
+                            company
                             gotest))
 
 (require 'go-projectile)
@@ -58,23 +60,25 @@
       (when goimports
         (setq gofmt-command goimports)))
 
-    ;; gofmt on save
-    (add-hook 'before-save-hook 'gofmt-before-save nil t)
-
     ;; stop whitespace being highlighted
     (whitespace-toggle-options '(tabs))
 
-    ;; Company mode settings
-    (set (make-local-variable 'company-backends) '(company-go))
-
-    ;; El-doc for Go
-    (go-eldoc-setup)
-
     ;; CamelCase aware editing operations
     (subword-mode +1))
 
-  (setq prelude-go-mode-hook 'prelude-go-mode-defaults)
+  ;; if yas is present, this enables yas-global-mode
+  ;; which provides completion via company
+  (if (fboundp 'yas-global-mode)
+      (yas-global-mode))
 
+  ;; configure lsp for go
+  (defun lsp-go-install-save-hooks ()
+    (add-hook 'before-save-hook #'lsp-format-buffer t t)
+    (add-hook 'before-save-hook #'lsp-organize-imports t t))
+  (add-hook 'go-mode-hook #'lsp-go-install-save-hooks)
+  (add-hook 'go-mode-hook #'lsp-deferred)
+
+  (setq prelude-go-mode-hook 'prelude-go-mode-defaults)
   (add-hook 'go-mode-hook (lambda ()
                             (run-hooks 'prelude-go-mode-hook))))