Add custom desktop minor mode handler for lsp-deferred

[LaurenceWarne]

Hi, I've been encountering some issues with lsp servers starting with desktop-save-mode despite me using lsp-deferred . I've been able to reproduce it minimally with configuration:

(desktop-save-mode 1)

(require 'package)
(let* ((no-ssl (and (memq system-type '(windows-nt ms-dos))
                    (not (gnutls-available-p))))
       (proto (if no-ssl "http" "https")))
  (add-to-list 'package-archives (cons "melpa" (concat proto "://melpa.org/packages/")) t))

(package-initialize)

(unless (package-installed-p 'use-package)
  (package-refresh-contents)
  (package-install 'use-package)
  (eval-when-compile (require 'use-package)))

(setq use-package-always-ensure t)

(use-package lsp-mode
  :init
  ;; set prefix for lsp-command-keymap (few alternatives - "C-l", "C-c l")
  (setq lsp-keymap-prefix "C-c l")
  :hook (;; replace XXX-mode with concrete major-mode(e. g. python-mode)
         (python-mode . lsp-deferred))

Then perform the following:

1. Open a python file, so that an lsp server starts
2. Switch back to scratch
3. Exit Emacs, in your desktop file lsp-mode should be in the buffer-minormodes section for the python file you opened
4. Opening Emacs starts a python lsp server despite me starting now in a scratch buffer

The proposed fix is to add lsp--buffer-deferred to desktop-locals-to-save and add a custom handler to desktop-minor-mode-handlers which uses this persisted variable to determine whether to use lsp-deferred or lsp-mode when re-opening a file from the saved desktop. I've been using it for a while and haven't had any issues.

Let me know what you think, Thanks (also I'm on 28.1 and the most recent lsp-mode commit).

[yyoncho]

I don't like the top level require. I would rather go with either adding this to the FAQ, or using (with-eval-after-load 'desktop ... . If you make it FAQ entry - I will let it go right away. If you prefer to have it on by default I will have to spend a bit more time trying to figure out what the actual issue is(ATM it is bit unclear to me). Let me know what you think.

[LaurenceWarne]

Yeah, with-eval-after-load should be used, I'll change that.

If you prefer to have it on by default I will have to spend a bit more time trying to figure out what the actual issue is(ATM it is bit unclear to me). Let me know what you think.

If you can reproduce the behaviour (is it expected?) I'd say the current behaviour is a bit counterintuitive 🙂 .

In terms of the issue, ff its helpful, my understanding is that once lsp-mode has been written to the minor mode list for a file in a desktop file, it's passed straight to desktop-create-buffer (when recreated) - at this point I'm not sure there's any discrimination as to if lsp-deferred was originally used or not.

[LaurenceWarne]

Possibly a simpler fix could be (add-to-list 'desktop-minor-mode-table '(lsp-mode nil)) so that desktop save mode will never try to restore lsp-mode.

[jo-so]

A better solution would be to restore lsp-mode by lsp-deferred.

  (defun lsp-deferred-restore-desktop-buffer (buf-locals)
    (lsp-deferred))

  (add-to-list 'desktop-minor-mode-handlers
               '(lsp-mode . lsp-deferred-restore-desktop-buffer))