bug#29478: [Patch] bug#29478: 26.0.90; `C-h k' followed by mouse clicks no longer shows down event

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Cc: acm@muc.de, 29478@debbugs.gnu.org, npostavs@users.sourceforge.net
> Date: Fri, 26 Jan 2018 17:00:15 -0500
> 
> >   <S-down-mouse-1> at that spot runs the command mouse-appearance-menu
> >   <S-mouse-1> at that spot is undefined
> >
> > I'd expect the second line not to appear.
> 
> About that, I wrote:
> 
>     OTOH, for text-terminals, we add a "(translated from <escape-sequence>)"
>     and we could do the same here (that's what my patch originally did, by
>     the way, and that's what I've been using all these years since I think
>     it's very valuable information), which would say:
>     
>        <C-H-mouse-1> (translated from <C-H-down-mouse-1> <C-H-mouse-1>)
>        at that spot is undefined
> 
> but I misremembered, the above also appears in vanilla Emacs.  Regarding
> your example:
> 
>     <S-down-mouse-1> at that spot runs the command mouse-appearance-menu
>     <S-mouse-1> at that spot is undefined
> 
> it's hard to do much better: the S-mouse-1 event is eaten by
> `mouse-appearance-menu` but it's basically impossible to determine
> that automatically.
> 
> And if you want to "not show undefined sequences", does that mean we
> don't say anything at all for `C-h k M-_` rather than "M-_ is undefined"?
> How 'bout `C-h c M-S-double-mouse-1` which with my code says (courtesy
> copy-next-command-output (!)):
> 
>     <M-S-mouse-1> (translated from <M-S-down-mouse-1> <M-S-mouse-1>) at that spot is undefined
>     <M-S-double-mouse-1> (translated from <M-S-double-down-mouse-1> <M-S-double-mouse-1>) is undefined
> 
> We can probably come up with some heuristic to keep "at least one line
> of output" or something, but I think it's more useful for the user to
> report all the events and their binding or lack thereof since we don't
> really know what the user is looking for.

I'd prefer the "undefined" lines to appear only if none of the
possible interpretations is bound to a command, yes.