Cannot change lsp-keymap-prefix with setq

[tjtrabue]

Hey everyone! I hope I'm not terribly off-base here. This is my first time reporting a bug on GitHub. First of all, let me say that I love lsp-mode! It's fantastic. Great job, everyone. This is an incredible technical accomplishment.

Describe the bug
When I use (setq lsp-keymap-prefix "C-c l") to change the prefix for executing lsp-mode commands, I cannot use my new keymap. When I check C-h v to view the value of lsp-keymap-prefix I see that it is indeed my new keybinding "C-c l", but again, this new keybinding does nothing when I attempt to use it. In fact, Emac's echo area reports "C-c l is undefined".

I do have a workaround. Using (define-key lsp-mode-map (kbd "C-c l") lsp-command-map) does work. I got the idea from projectile's documentation detailing how to map their prefix sequence. Any idea why this method works for me while the official method seems to do nothing?

Thank you so much!

To Reproduce

1. Minimalist init.el file:

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

(use-package lsp-mode
  :ensure t
  :init (setq lsp-keymap-prefix "C-c l")
  ::hook
  (((sh-mode) . lsp)
    (lsp-mode . lsp-enable-which-key-integration))
  :commands lsp
  :config
  (require 'lsp-clients)
  (setq lsp-print-io t
    lsp-enable-snippet t
    lsp-enable-semantic-highlighting t))

2. Open any file supported by a language server and client within lsp-mode (I used a Bash file with bash-language-server)

3. Attempt to use the new keymapping "C-c l" to issue an LSP command.

Expected behavior
I expect to see a prompt for an LSP command appear in the echo area. However, I get "C-c l is undefined".

Which Language Server did you use
bash-language-server

OS
Arch Linux. Kernel version: 5.4.26-1-lts

Emacs version 28.0.50

Error callstack
The only error I get is that "C-c l is undefined." The lsp-mode functions appear to work just fine when I call them using M-x <function-name>. It's only the keymap that isn't working properly.

[kiennq]

lsp-keymap-prefix is mostly for documentation of which-key integration only.
If you want to customize the key binding for lsp commands, you should key bind lsp-command-map.
For example:

(use-package lsp-mode
  :ensure t
  :defer t
  :hook (lsp-mode . (lambda ()
                      (let ((lsp-keymap-prefix "C-c l"))
                        (lsp-enable-which-key-integration))))
  :init
  (setq lsp-keep-workspace-alive nil
        lsp-signature-doc-lines 5
        lsp-idle-delay 0.5
        lsp-prefer-capf t
        lsp-client-packages nil)
  :config
  (define-key lsp-mode-map (kbd "C-c l") lsp-command-map))

[yyoncho]

You may use @kiennq suggestion or move setq on top-level as suggested by the updated docs.

[artemkovalyov]

@tjtrabue , you can also use :bind-keymap from use-package to achieve that: https://github.com/jwiegley/use-package#binding-to-keymaps

  :bind-keymap ("s-SPC" . lsp-command-map)
  :bind (:map lsp-mode-map
              ("s-r"  . lsp-rename))

[xushijie]

lsp-keymap-prefix is mostly for documentation of which-key integration only. If you want to customize the key binding for lsp commands, you should key bind lsp-command-map. For example:

(use-package lsp-mode
  :ensure t
  :defer t
  :hook (lsp-mode . (lambda ()
                      (let ((lsp-keymap-prefix "C-c l"))
                        (lsp-enable-which-key-integration))))
  :init
  (setq lsp-keep-workspace-alive nil
        lsp-signature-doc-lines 5
        lsp-idle-delay 0.5
        lsp-prefer-capf t
        lsp-client-packages nil)
  :config
  (define-key lsp-mode-map (kbd "C-c l") lsp-command-map))

Since C-c l involves three keys, and my keyboard(thinkpad X1E) has a special key: Fn.
Is it possible to replace C-c l with Fn? I tried C-c l with Fn in your sample script, but fail...