bug#49784: 27.2; mouse-2 error with "No cross-reference here"

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Robert Morelli <morelli@flux.utah.edu>,  49784@debbugs.gnu.org
> Date: Fri, 30 Jul 2021 20:54:08 +0200
> 
> Especially with this not very helpful command:
> 
> ;; The doc string is meant to explain what buttons do.
> (defun help-follow-mouse ()
>   "Follow the cross-reference that you click on."
>   (interactive)
>   (error "No cross-reference here"))
> 
> I guess the point is to...  not say
> 
> Buffer is read-only: #<buffer *Help*>
> 
> to be helpful?  It might just confuse more than it helps.

Perhaps the comment before the function hints on why this was done
that way.  IOW, if this binding didn't exist, what would C-h show for
mouse-2, and how?