Guard terminal parameter in XTerm mouse mode

It has been observed (in the HTerm terminal emulator) that the
event stored in the 'xterm-mouse-last-down' terminal parameter gets
overwritten during a mouse drag operation, causing Emacs to attempt to
synthesize the non-existing <drag-mouse-0> event.  Copy the event into
the terminal parameter to protect against such modifications.

* lisp/xt-mouse.el (xterm-mouse-translate-1): Guard against modification
of input event list.

1 files changed, 5 insertions, 1 deletions

diff --git a/lisp/xt-mouse.el b/lisp/xt-mouse.el
index a2b64019f97..15fc6de6a42 100644
--- a/lisp/xt-mouse.el
+++ b/lisp/xt-mouse.el
@@ -70,7 +70,11 @@ http://invisible-island.net/xterm/ctlseqs/ctlseqs.html)."
       (cond
        ((null event) nil)               ;Unknown/bogus byte sequence!
        (is-down
-        (setf (terminal-parameter nil 'xterm-mouse-last-down) event)
+        (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))
         vec)
        (is-move vec)
        (t