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

[Philipp Stephani <phst@google.com>]

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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.
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