bug#60530: 28.2; Add tools to find keymaps that bind a given command

[Eli Zaretskii]

> From: Ruijie Yu <ruijie@netyu.xyz>
> Cc: spd@toadstyle.org, 60530@debbugs.gnu.org
> Date: Mon, 20 Feb 2023 20:01:27 +0800
> 
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Cc: 60530@debbugs.gnu.org
> >> Date: Mon, 20 Feb 2023 15:07:09 +0800
> >> From:  Ruijie Yu via "Bug reports for GNU Emacs,
> >>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> >>
> >> I saw this message long ago, but recently I came across a situation
> >> where I wanted to know if a command was bound in *some* keymap whose
> >> name I didn't know, and this would be quite a helpful feature for me
> >> personally (pun intended).
> >
> > Isn't that what where-is and/or where-is-internal already do?
> 
> No, not quite.  The functions where-is{,-internal} only look for
> *currently active keymaps*, whereas my intention was to look for all
> keybinds for the specified command, be it active or not.

But that's impossible in principle, because loading some package could
produce a binding for a command, and you don't know which packages
will be loaded into a session before they are actually loaded.

Or what am I missing?

> The following is my reason to want this feature.  I use pyim, an input
> method that shows candidate words in a small frame (which I believe is
> called posframe?), which has `pyim-mode-map' enabled.  Then, while
> typing, I want to know how to call the `pyim-next-page' command without
> going into pyim source.
> 
> If I type M-x where-is, this frame disappears, and I am dropped back
> into the editing buffer, which does not have `pyim-mode-map' enabled.
> Hence, `where-is' does not show anything bound for `pyim-next-page',
> because it indeed is not bound globally.  FTR, C-h b does not work
> either.

If what where-is does doesn't suit your needs for reasons of its UI or
how it switches buffers, you could extract (parts of) its code and
make a similar function which presents the results in a way that
doesn't interrupt your workflow.  My point in mentioning the existing
commands is that they already show how to find bindings for an
arbitrary command, so you could reuse some or all of that code for
your purposes (which sound very similar to me).