Emacs eglot reload after cabal file is changed

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1

hi guys

question for those who use emacs

how you make eglot restart after cabal file is changed. Every time when I need to change something in cabal I have to manually restart eglot

here is my config

(use-package eglot
  :ensure t
  :config
  (add-hook 'haskell-mode-hook 'eglot-ensure)
  (add-hook 'haskell-mode-hook 'company-mode)
  (add-hook 'haskell-mode-hook 'turn-on-haskell-indentation)
  (custom-set-variables
   '(haskell-stylish-on-save t)
   '(haskell-tags-on-save t)
   '(haskell-process-suggest-remove-import-lines t)
   '(haskell-process-auto-import-loaded-modules t)
   '(haskell-process-log t))
  (eval-after-load 'haskell-mode '(progn
				    (define-key haskell-mode-map (kbd "C-c C-l") 'haskell-process-load-or-reload)
				    (define-key haskell-mode-map (kbd "C-c C-z") 'haskell-interactive-switch)
				    (define-key haskell-mode-map (kbd "C-c C-o") 'haskell-compile)
				    (define-key haskell-mode-map (kbd "C-c v c") 'haskell-cabal-visit-file)))
  :custom
  (eglot-autoshutdown t)  ;; shutdown language server after closing last file
  (eglot-confirm-server-initiated-edits nil)  ;; allow edits without confirmation
  (eglot-send-changes-idle-time 0.1)
)

(let ((my-cabal-path (expand-file-name "~/.cabal/bin")))
  (setenv "PATH" (concat my-cabal-path path-separator (getenv "PATH")))
  (add-to-list 'exec-path my-cabal-path))

(add-hook 'after-save-hook 'my/eglot-reconnect-on-cabal-change)
(add-hook 'find-file-hook 'my/eglot-reconnect-on-cabal-change)

(defun my/eglot-reconnect-on-cabal-change ()
  "Reconnect Eglot when a cabal file is changed."
  (when (and (bound-and-true-p eglot--managed-mode)   ;; Check if eglot is active
             (string-match-p "\\.cabal\\'" buffer-file-name))
    (message "Triggering eglot-reconnect for cabal file")  ;; Debug message
    (eglot-reconnect)))  ;; Use eglot-reconnect instead of eglot-reload

I’ve asked chatGPT about it and she proposed to add extra hooks + function my/eglot-reconnect-on-cabal-change but it doesn’t work

how you make eglot restart after changing cabal?

please, help! it’s a pain to restart it manually every time

P.S I know that my config might have mistakes or something, so please, I need your help

OS: macOS
HSL: 2.7.0.0 (GHC: 9.2.8)

2

Kind of seems like a HLS bug/missing feature, that it’s not picking up .cabal file changes?

I’m guessing the reason your hook is not being triggered is because the test for (bound-and-true-p eglot--managed-mode) fails in the .cabal buffer – at least it does for me (while succeeding in a .hs file of the same project after I’ve done M-x eglot). By default, eglot doesn’t run a language server for .cabal files.

A workaround would be to check if the file is in a project where an eglot server was started:

(when (and (gethash (project-current) eglot--servers-by-project) ; should be truish (non-nil) if eglot was started in the project that the current buffer is in
           (string-match-p "\\.cabal\\'" buffer-file-name))

However HLS seems to support .cabal files too these days, so maybe a better solution would be to enable support for eglot in haskell-cabal-mode buffers. Put this in your eglot :config

(when-let ((entry (assoc 'haskell-mode eglot-server-programs)))
      (setcar entry '(haskell-cabal-mode haskell-mode)))

and you can keep the simple (bound-and-true-p eglot--managed-mode) test. This also gives you HLS-checking of .cabal files.

In case, I’m sure it’ll have some kind of hickups if you save twice fast or something (while HLS is still starting up).

3

This was implemented, but is currently broken.

Personally, I’m quite happy with it being broken. I often make trivial changes to Cabal files (e.g. metadata or temporary debugging dependencies) and HLS reloads are expensive.