An IDE should at least aid with

• Auto-completion (a.k.a Intellisense)
• Jump to definition
• On-the-fly error checks

Additionally it’d be good to have

• Context-sensitive document lookup
  • Show variable and function type
  • Show function description
• Auto-run gofmt on save
• Auto-add/remove used/unused packages on file save

We’ll get these working for Go on Emacs using LSP. It’s no secret that Emacs’ LSP support is top notch.

We assume Go 1.17+ i.e. with full modules support and GO111MODULE unset¹.

Go, please!

Yeah, that’s the name of gopls, Go’s LSP server 😉. If your package manager doesn’t have it, go install it:

go install golang.org/x/tools/gopls@latest

Emacs Setup

Install go-mode package from Melpa and hook it to lsp-mode:

(use-package go-mode
  :mode "\\.go\\'"
  :config
  (defun my/go-mode-setup ()
    "Basic Go mode setup."
  (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 #'my/go-mode-setup))

(use-package lsp-mode
  :ensure t
  :commands (lsp lsp-mode lsp-deferred)
  :hook ((rust-mode python-mode go-mode) . lsp-deferred)
  :config
  (setq lsp-prefer-flymake nil
        lsp-enable-indentation nil
        lsp-enable-on-type-formatting nil
        lsp-rust-server 'rust-analyzer)
  ;; for filling args placeholders upon function completion candidate selection
  ;; lsp-enable-snippet and company-lsp-enable-snippet should be nil with
  ;; yas-minor-mode is enabled: https://emacs.stackexchange.com/q/53104
  (lsp-modeline-code-actions-mode)
  (add-hook 'lsp-mode-hook #'lsp-enable-which-key-integration)
  (add-to-list 'lsp-file-watch-ignored "\\.vscode\\'"))

Verify

Make sure gopls is in $PATH. If you’ve go install-ed, make sure to add $GOPATH/bin to $PATH. Since projects use modules now, I use $GOPATH only to house Go tools which aren’t part of the official toolchain. Similar to ${HOME}/.cargo for Rust, I set ${HOME}/.go as my $GOPATH and fix $PATH.

Read go help gopath and go help install for details.

Add entries with a trailing slash; missing it may lead to issues.

Usage

• If you’re not open an existing source file, be sure to save your fresh buffer.
  • Without saving you’d get warnings from tools
• Auto-completion
  • Test it by importing fmt and type fmt.
  • It should list the package’s public members
  • Cycle through the options with M-n and M-p
  • Additionally it’d also show the function prototype in the mini-buffer
• Jump to definition
  • When point is atop a function name, press M-.
  • This should open the file where it’s defined and seek to the definition
  • To return back to original place press M-,
• Flycheck, with no setup, does a good job of flagging warnings/errors
  • flycheck-verify-setup is useful at times
• Context-sensitive document lookup
  • Positioning point on a variable/function should show its type in the minibuffer
  • To get a detailed description of a function do godoc-at-point (needs godoc)
  • You could bind it to a key combo; it’s fairly handy
• Auto-formatting
  • When you save the buffer it auto-formats with gofmt
• Auto-include/exclude
  • At the top-level, include packages you wouldn’t reference
  • In functions from packages you didn’t import
  • Save the buffer! Redundant imports are deleted, needed ones are added 😉
  • Go is strict about unused imports and this helps

This is a stable and light setup. I’m happy with it for now.

References

1. go help install
2. go help gopath
3. gopls Documentation