Re: [Emacs-diffs] emacs-25 d4e1549: Guard terminal parameter in XTerm mouse mode

[Eli Zaretskii <eliz@gnu.org>]

> From: Philipp Stephani <phst@google.com>
> Date: Wed, 23 Nov 2016 12:20:16 +0000
> 
> Stefan Monnier <monnier@iro.umontreal.ca> schrieb am Mi., 23. Nov. 2016 um 02:08 Uhr:
> 
>  > + (setf (terminal-parameter nil 'xterm-mouse-last-down)
>  > + ;; EVENT might be handed back to the input queue, which
>  > + ;; might modify it. Copy it into the terminal parameter
>  > + ;; to guard against that.
>  > + (copy-sequence event))
> 
>  Do you have further information about when/where events might be
>  modified in place? It sounds like a risky operation.
> 
> I assume it's in the code that translates consecutive mouse-down events to mouse-movement events. It's
> easy to reproduce in HTerm: without the patch, dragging the mouse while holding a button causes
> "drag-mouse-0" events to be generated. These come from spurious mouse-movement events in
> xterm-mouse-last-down. Since nothing places these events explicitly there, the root cause must be that the
> event list is overwritten.
> Agreed that the input loop probably shouldn't modify event objects. But it might be a necessary optimization
> somewhere. Unfortunately I wasn't able to find the specific piece of code responsible for this modification.

Does this have to be applied to the release branch?  If so, can you
tell why?