Re: What's happened to M-<tab> `completion-at-point'?

[Alan Mackenzie]

Hello, Eli.

On Wed, May 04, 2022 at 21:55:28 +0300, Eli Zaretskii wrote:
> > Date: Wed, 4 May 2022 18:13:30 +0000
> > Cc: emacs-devel@gnu.org
> > From: Alan Mackenzie <acm@muc.de>

> > > >     [backtab] is undefined

> > > And what does "C-h l" show after that?

> > If I first press ESC TAB and C-h l, followed by C-M-i and C-h l, I get
> > this:

> >  ESC TAB ;; nil
> >  C-h l   ;; view-lossage
> >  ESC TAB ;; nil
> >  C-h l   ;; view-lossage

> So who is converting this to <backtab>?

I don't know, yet.

> > I think I've found the problem.  A new version of ncurses was
> > installed on my machine on 2022-05-01.  It contains a version of
> > terminfo, specifically /etc/terminfo/l/linux.

> > The new version is ncurses-6.3_p20211106.  The old version was
> > ncurses-6.2_p20210619.

> > So, possibly we need to amend Emacs (? src/term.c) to work properly on
> > this version of the Linux console.

> Amend how?  I still don't understand where did <backtab> come from.
> If you do understand, can you describe that?

I don't understand it either, yet.  To be sure that terminfo is the
problem, I'll have to do something like reinstalling the old version of
ncurses, and seeing the problem is no longer there.

But in src/term.c L1258 appears:

      {"kB", "backtab"},    /* terminfo */

The "kB" is a terminfo code for back-tab, and the "backtab" might
somehow be the source for the "[backtab] is undefined" error message.

I'm still at an early stage of understanding this bug.

-- 
Alan Mackenzie (Nuremberg, Germany).