bug#61241: 29.0.60; Incoherent last_mouse_window (xterm.c) between XInput and XInput 2

["Adrián Medraño Calvo" <adrian@medranocalvo.com>]

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For the implementation of `mouse-autoselect-window', the entered window
is remembered and then compared when an mouse motion event is received.
Up to Emacs 28, this value was stored in a static local variable named
`last_mouse_window' in the block handling MotionNotify within
`handle_one_xevent'.  With the introduction of XInput 2,
`handle_one_xevent' was adjusted to account for XI_Motion events, with
the oversight that a new local static `last_mouse_window' variable was
declared in the new handler block for XI_Motion.  As a result, when
Emacs receives motion events from XInput and XInput2 sources
alternatively the value of each `last_mouse_window’ differs, leading to
the window under the motion sometimes not being selected, as the
value `last_mouse_window' is out-of-date for the particular XInput
version.

This bug impacts the GNU ELPA package EXWM.  EXWM tries to extrapolate
applicable Emacs functionality to X window management; among others
assigns an Emacs buffer to each managed X window, and positions the X
window over the Emacs window in which the buffer is displayed.  When
`mouse-autoselect-windows’ and the user moves the mouse pointer over one
X window managed by EXWM, this X window receives the mouse events and not
Emacs, therefore the Emacs window is not selected.  In order to overcome
this, EXWM sends a synthetic MotionNotify event to Emacs.

The attached patch fixes the issue.

Thank you,
Adrián Medraño Calvo.


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From e16d6ddbfdc4110fbbbcf763cff5a72b0f0df92c Mon Sep 17 00:00:00 2001
Message-Id: <e16d6ddbfdc4110fbbbcf763cff5a72b0f0df92c.1675376734.git.adrian@medranocalvo.com>
From: =?UTF-8?q?Adri=C3=A1n=20Medra=C3=B1o=20Calvo?=
 <adrian@medranocalvo.com>
Date: Wed, 1 Feb 2023 00:00:00 +0000
Subject: [PATCH] Fix `mouse-autoselect-window' for alternating XInput and
 XInput 2 events

* src/xterm.c (handle_one_xevent): Move `last_mouse_window' to
main function scope to share value between XInput and XInput 2
handlers.
---
 src/xterm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/xterm.c b/src/xterm.c
index 6a4b84babe4..dd20c8c7fe5 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -18364,6 +18364,9 @@ handle_one_xevent (struct x_display_info *dpyinfo,
   GdkDisplay *gdpy = gdk_x11_lookup_xdisplay (dpyinfo->display);
 #endif
   int dx, dy;
+  /* Holds the last window the mouse moved over, used for
+     `mouse-autoselect-window' */
+  static Lisp_Object last_mouse_window;
 
   /* Avoid warnings when SAFE_ALLOCA is not actually used.  */
 #if defined HAVE_XINPUT2 || defined HAVE_XKB || defined HAVE_X_I18N
@@ -20677,8 +20680,6 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 		&& (f == XFRAME (selected_frame)
 		    || !NILP (focus_follows_mouse)))
 	      {
-		static Lisp_Object last_mouse_window;
-
 		if (xmotion.window != FRAME_X_WINDOW (f))
 		  {
 		    x_translate_coordinates (f, xmotion.x_root, xmotion.y_root,
@@ -22587,7 +22588,6 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 		      && (f == XFRAME (selected_frame)
 			  || !NILP (focus_follows_mouse)))
 		    {
-		      static Lisp_Object last_mouse_window;
 		      Lisp_Object window = window_from_coordinates (f, ev.x, ev.y, 0, false, false);
 
 		      /* A window will be autoselected only when it is not
-- 
2.39.1


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In GNU Emacs 29.0.60 (build 1, x86_64-apple-darwin22.2.0, cairo version
 1.17.6) of 2023-01-26 built on amcmac
Repository revision: f8c95d1a7681e861fc22d2a040cda0ddfe23eff4
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101006
System Description:  macOS 13.2

Configured using:
 'configure --prefix=/Volumes/sys/repos/emacs-cairo/rel
 --without-makeinfo --without-dbus --without-ns --with-x-toolkit=no
 --with-cairo
 PKG_CONFIG_PATH=/opt/X11/lib/pkgconfig:/usr/local/opt/freetype/lib/pkgconfig:/usr/local/opt/fontconfig/lib/pkgconfig:/usr/local/opt/ncurses/lib/pkgconfig:/usr/local/opt/libxml2/lib/pkgconfig:/usr/local/Cellar/jpeg/9d/lib/pkgconfig:/usr/local/Cellar/libtiff/4.3.0/lib/pkgconfig:/usr/local/opt/harfbuzz/lib/pkgconfig/:/usr/local/opt/harfbuzz/lib/pkgconfig/
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Configured features:
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MODULES NOTIFY KQUEUE OLDXMENU PDUMPER PNG RSVG SQLITE3 THREADS WEBP X11
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Important settings:
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Load-path shadows:
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