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

[Philipp Stephani <phst@google.com>]

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Eli Zaretskii <eliz@gnu.org> schrieb am Mi., 23. Nov. 2016 um 16:54 Uhr:

> > 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?
>

It's a very annoying and highly visible bug, and the fix is trivial and
cannot possibly break anything.
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