Re: Functions which are mode dependent

[Yuri Khan <yuri.v.khan@gmail.com>]

On Sat, 24 Aug 2024 at 16:46, Heime <heimeborgia@protonmail.com> wrote:
>
> Is this be the correct way for a minor mode to use the variable
> tema-expr-elisp for imenu-generic-expression that will be applied
> when enabling tema-minor-mode on a buffer in emacs-lisp-mode ?

No. Consider:

1. You open an Elisp file (C-x C-f /home/me/some.el RET).
2. A buffer is created.
3. The file’s contents are loaded into the buffer.
4. The buffer switches to emacs-lisp-mode.
5. emacs-lisp-mode runs emacs-lisp-mode-hook. At this point, the hook
is empty so nothing special happens.
6. You enable your minor mode (M-x tema-minor-mode RET).
7. It adds tema-imenu-expr-elisp to emacs-lisp-mode-hook, but at this
point it is too late for your current buffer.

Observed result: your minor mode is enabled in the buffer of some.el,
but its configuration is not applied.

Further:

8. You open another Elisp file (C-x C-f /home/me/other.el RET).
9. A buffer is created.
10. The file’s contents are loaded into the buffer.
11. The buffer switches to emacs-lisp-mode.
12. emacs-lisp-mode runs emacs-lisp-mode-hook. The hook contains the
function added by enabling the minor mode in another buffer, so that
function runs and modifies imenu-generic-expression.

Observed result: In the buffer of other.el, tema-minor-mode is not
enabled, yet its configuration has been applied.


Now drop your focus on the solution. What problem are you solving? Why
do you want to modify imenu-generic-expression for emacs-lisp-mode
buffers but only sometimes?


> (defvar tema-expr-elisp
>   '(("Functions" "^\\s-(defun\\s-+\\(\\_<.?\\_>\\)" 1)))
>
> (defun tema-imenu-expr-elisp ()
>   "Set up a custom imenu expression for the current buffer."
>   (setq-local imenu-generic-expression tema-expr-elisp))
>
> ;;;###autoload
> (define-minor-mode tema-minor-mode
>   "DESC."
>   :init-value nil
>   :lighter " Tema"
>
>   (if tema-minor-mode
>       (progn
>         (add-hook 'sh-mode-hook #'tema-imenu-expr-sh)
>         (add-hook 'emacs-lisp-mode-hook #'tema-imenu-expr-elisp))
>     (remove-hook 'sh-mode-hook #'tema-imenu-expr-sh)
>     (remove-hook 'emacs-lisp-mode-hook #'tema-imenu-expr-elisp)))