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

[Ergus via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Hi:

1)

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.

So far with nested keymaps this could be solved, but there is not any
clean way to do that; so my request is to extend the new keymap-set to
set keymap without a prefix in another...

The idea is more or less to enable the developers of packages to do
something like:

```
(defvar-keymap my-mode-isearch-map
     ...)

(define-minor-mode my-mode
    :global t
    (if my-mode
        (keymap-set isearch-mode-map <something> my-mode-isearch-map)
      (keymap-unset isearch-mode-map <something>)))
```

With that then could be trivial to implemented something like
use-packages :bind, so

(define-minor-mode my-mode
    :global t
    :keymap (my-mode-map
             :map isearch-mode-map my-mode-isearch-map))


or similar... I am wondering how nobody have requested this before, when
it is a very common issue I find in many packages around.

2)

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...

To restore the original value they check if the current vars's value is
the same that was set (to assert it was not changed latter).

This way if I try fido-mode and I don't like it, then not restart is
needed to assert that completion-styles is what I had before...

Maybe we could consider to add some api for these functionalities...

Does it makes sense??




In GNU Emacs 29.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.31, cairo version 1.17.4)
 of 2022-02-20 built on Ergus
Repository revision: e6f541f2383cf860c6a2d6c8d366c21a3b8de2d0
Repository branch: master
System Description: Arch Linux

Configured using:
 'configure --prefix=/home/ergo/.local/ --with-mailutils --with-json
 --with-x-toolkit=gtk3 --with-xft --with-wide-int --with-modules
 --with-cairo --with-harfbuzz --with-native-compilation --with-pgtk'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER
PGTK PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS
WEBP XIM GTK3 ZLIB

Important settings:
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  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
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  eldoc-mode: t
  show-paren-mode: t
  mouse-wheel-mode: t
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  context-menu-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
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  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
~/gits/emacs_clones/composable/composable-mark hides /home/ergo/.config/emacs/elpa/composable-20201024.1458/composable-mark
~/gits/emacs_clones/composable/composable hides /home/ergo/.config/emacs/elpa/composable-20201024.1458/composable
/home/ergo/.config/emacs/elpa/transient-20220216.2303/transient hides /home/ergo/.local/share/emacs/29.0.50/lisp/transient

Features:
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dbusbind inotify dynamic-setting system-font-setting font-render-setting
cairo gtk pgtk lcms2 multi-tty make-network-process native-compile
emacs)

Memory information:
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