bug#57163: completing-read not allow cycling of the options by default

[Eli Zaretskii]

> Date: Sat, 13 Aug 2022 18:15:26 +0000
> From: uzibalqa <uzibalqa@proton.me>
> Cc: michael_heerdegen@web.de, 57163@debbugs.gnu.org
> 
> > > Debugger entered--Lisp error: (user-error "End of defaults; no next item")
> > > signal(user-error ("End of defaults; no next item"))
> > > user-error("End of defaults; no next item")
> >
> >
> > Well, don't set debug-on-error, then.
> >
> > > After that, doing M-p gives [M-p is undefined]
> >
> >
> > Because you are in the debugger, in recursive-edit. Type C-] to exit
> > that.
> 
> Should it be a user-error though?

A low-level API such as completing-read has no business in deciding
which errors are user-errors and which aren't.  That's for the calling
application to decide.

>  there any scheme to set another keybinding
> for `M-n` and `M-p` for things like completing-read?  Being able to use [up] 
> and
> [down] would be both convenient and intuitive (particularly people who use 
> packages
> like company-mode), but cannot see that completing-read could allow that.

<UP> and <DOWN> arrow keys work here, they do the same as M-p and M-n.