bug#68213: 30.0.50; completion-preview-tests failure in --without-x build

[Eli Zaretskii <eliz@gnu.org>]

> From: Eshel Yaron <me@eshelyaron.com>
> Cc: Eli Zaretskii <eliz@gnu.org>,  68213@debbugs.gnu.org
> Date: Wed, 03 Jan 2024 08:20:37 +0100
> 
> john muhl <jm@pub.pink> writes:
> 
> > Eshel Yaron <me@eshelyaron.com> writes:
> >
> >> FWIW, I was going to suggest the attached patch, following how
> >> flymake.el handles this.  But if the current solution works, that seems
> >> just as good.
> >>
> >   lisp/completion-preview-tests.el:23:2: Error: Duplicate
> >   definition for key: "<mouse-5>" (keymap (mouse-5 .
> >   completion-preview-prev-candidate) (down-mouse-2 .
> >   completion-at-point) (C-down-mouse-1 . completion-at-point)
> >   (down-mouse-1 . completion-preview-insert))
> 
> Ah I can see that, thanks.  IMO `defvar-keymap` is too strict in this
> case: the "duplicate" definition is not erroneous, it just happens to be
> redundant with some values of the `mwheel` variables.  There's been some
> discussion around that in bug#56873, FWIW.  So ISTM that the best way
> forward would be to make `defvar-keymap` more lax, perhaps optionally
> with a `:lax` keyword argument or some such.  Any other ideas?

Please tell more, as I don't think I follow.  Specifically:

  . does the problem happen only in a --without-x build?
  . what "duplicate" definitions do we have there and why?

Thanks.