bug#54074: 29.0.50; Feature request emacs keymap-set and minor-modes

[Ergus]

On Sun, Feb 20, 2022 at 08:39:16PM +0100, Lars Ingebrigtsen wrote:
> Ergus <spacibba@aol.com> writes:
>
> > Recently I have seen that many packages have a pattern where a global
> > minor mode adds a set of keybindings to another (like isearch or
> > minibuffer). The issue comes when they want to disable the mode, because
> > sometimes they need to iterate or loop over, and then emacs looses the
> > previous binding unless they also adds more code to remember it when set
> > and then bring it back when unset.

Hi Lars.. thanks for replying!

> I'm not sure I understand the use case.  Isn't the way to do this just
> to have my-mode add itself to isearch-mode-hook, and then have my-mode
> have a minor mode keymap with the prefix it uses?
Yes this is actually the common way to do it, but it is cumbersome with
no reason for simpler cases... and when more than one keymap can be
affected.

Basically I mean to have a way to add an entry: (keymap …) to another...

Because from the manual:

"If an element of a keymap is itself a keymap, it counts as if this inner
keymap were inlined in the outer keymap."

So, simpler cleaner and eventually not needing execute or start a mode
every time in a hook...

Now keymap-set allows to add a command or keymap to a prefix in another,
but not just append a keymap as is with no prefix and then remove it
completely in a clean way...


> > Something similar happens to some variables that are modified in minor
> > modes and then should be restored... this forces sometimes to restart
> > emacs... (for example completion-styles in fido-mode or some hooks that
> > are always added and then need to be removed... all these is very
> > mechanic and increases code and sources of errors...).
> >
> > The best approach for this one is to save the original value in an alist
> > and assign with a wrapper around setq...  and use a loop when disabling
> > the mode to restore the original values.... it is not perfect, but works
> > in many cases...
>
> I don't think there's any general mechanism that's possible for this.
> Any package may mogrify any variable (destructively or not), and only
> the package can know what it has to do to bring things back to normal
> when the package is switched off.

The common is just to save and the restore... isn't it the typical idea
behind a mode? Right now the modes cleanup is a source of issues and
code replication here and there for many mechanical thinks like
add-hook/remove-hook, set variable, unset them, and so on... when the
general idea is that all that may follow the same philosophy than
keybindings set-unset...

Best,
Ergus