Subject: bug#17439: 24.3.50; run-with-idle-timer runs on focus-out

From: Juri Linkov <[email-masked]>
Date: Thu, 08 May 2014 23:45:27 +0300

Some change a few months ago introduced a significant inconvenience.
After switching to another application, the focus returns back to Emacs.
It happens when using `mouse-avoidance-mode' customized to `banish'.
This mode relies on `run-with-idle-timer' that moves the mouse cursor
on a new input.  This caused no problems in prior releases.

However, now input events include a new event type `focus-out',
so the mouse cursor is moved on switching from Emacs frame
(and the new mouse cursor position puts the focus back
due to specific configuration).

This code illustrates the problem:

(defun test () (message "%S" last-input-event))
(setq timer (run-with-idle-timer 0.1 t 'test))

On switching out it prints to *Messages*:

(focus-in #<frame emacs@localhost 0x1121908>)
(focus-out #<frame emacs@localhost 0x1121908>)

This specific problem can be fixed by this patch:

=== modified file 'lisp/avoid.el'
--- lisp/avoid.el	2014-01-31 06:42:29 +0000
+++ lisp/avoid.el	2014-05-08 20:39:59 +0000
@@ -343,7 +343,8 @@ (defun mouse-avoidance-ignore-p ()
 		 (let ((modifiers (event-modifiers (car last-input-event))))
 		   (or (memq (car last-input-event)
 			     '(mouse-movement scroll-bar-movement
-					      select-window switch-frame))
+					      select-window switch-frame
+					      focus-in focus-out))
 		       (memq 'click modifiers)
 		       (memq 'double modifiers)
 		       (memq 'triple modifiers)

PS: it seems there are other places that check only for `switch-frame',
and not for new event types `focus-in' and `focus-out'.  But maybe
this problem occurs only in `run-with-idle-timer' because switching out
doesn't emit the event on its own, i.e. `read-event' doesn't return it.