bug#74404: [PATCH] Give Completion Preview bindings higher precedence

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 17 Nov 2024 17:30:47 +0100
> From:  Eshel Yaron via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Whenever Completion Preview mode shows a completion preview, it also
> activates keybindings for commands that interact with that preview, most
> notably TAB is bound to completion-preview-insert, which inserts the
> suggested completion.  This is implemented via a minor mode
> completion-preview-active-mode whose keymap provides these bindings, and
> which is enabled when the preview is displayed. 
> 
> This all works well, except for when another minor mode, foo-mode, is
> enabled, whose keybindings conflict with these active preview bindings.
> If foo-mode is defined after completion-preview-active-mode, i.e. if
> foo.el is loaded after completion-preview.el, then foo-mode comes first
> in minor-mode-map-alist and takes precedence over the bindings in
> completion-preview-active-mode-map.
> 
> This happens, for example, with eshell-cmpl-mode, a minor mode that is
> enabled by default in Eshell, which binds TAB to completion-at-point.
> So currently Completion Preview mode doesn't work as expected in Eshell:
> when you try to accept the suggested completion (with TAB), you get
> completion-at-point instead of completion-preview-insert.
> 
> To fix this issue, we need to give the active completion preview
> bindings higher precedence than keymaps of minor modes that where
> defined after loading completion-preview.el.  The patch below does that
> by using minor-mode-overriding-map-alist.  Any thoughts?

Can't you instead use the 'keymap' text or overlay property?  That
would avoid the "arms race" of precedences.

Adding Stefan, in case he has comments or suggestions.