GNU bug report logs - #78897
Ediff 2.81.6; Window restoration with ediff-before-setup-hook doesn't work for ediff-regions-linewise

Previous Next

To reply to this bug, email your comments to 78897 AT debbugs.gnu.org.
There is no need to reopen the bug first.

Toggle the display of automated, internal messages from the tracker.

Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Aaron Zeng <azeng <at> janestreet.com>
To: kifer <at> cs.stonybrook.edu, bug-gnu-emacs <at> gnu.org
Cc: app-emacs-dev <at> janestreet.com
Subject: Ediff 2.81.6; Window restoration with ediff-before-setup-hook
 doesn't work for ediff-regions-linewise
Date: Wed, 25 Jun 2025 16:40:51 -0400

ediff-before-setup-hook's docstring suggests using it to save and
restore the window configuration prior to invoking an Ediff command.
Users at my site have an equivalent to the following hooks:

(defvar my-saved-window-configuration nil)
(add-hook 'ediff-before-setup-hook
          (lambda ()
            (setq my-saved-window-configuration (current-window-configuration))))
(add-hook 'ediff-quit-hook
          (lambda ()
            (set-window-configuration my-saved-window-configuration)
            (setq my-saved-window-configuration nil)))

This works fine for most Ediff commands but does not work correctly
with ediff-regions-linewise and ediff-regions-wordwise.  You can
reproduce the behavior from emacs -Q:

1. emacs -Q
2. Evaluate the above snippet
3. M-x ediff-regions-linewise (select an arbitrary pair of buffers and
   regions like selecting *scratch* twice)
4. Press q

After quitting, the original window configuration is not restored.  In
particular, the window is split vertically with a short window below
the selected taller one.

I believe this is because those commands use
ediff-clone-buffer-for-region-comparison to prompt for regions as diff
input, and that involves adjusting the window configuration a few
times.  The following patch seems to fix the behavior (edited to
remove the indentation diff for brevity):

diff --git a/lisp/vc/ediff-util.el b/lisp/vc/ediff-util.el
index a2c9b6f50ec..16878cf779f 100644
--- a/lisp/vc/ediff-util.el
+++ b/lisp/vc/ediff-util.el
@@ -3247,6 +3247,7 @@ ediff-save-buffer
 
 ;; idea suggested by Hannu Koivisto <azure <at> iki.fi>
 (defun ediff-clone-buffer-for-region-comparison (buff region-name)
+  (save-window-excursion
     (let ((cloned-buff (ediff-make-cloned-buffer buff region-name))
 	  (pop-up-windows t)
 	  wind
@@ -3285,7 +3286,7 @@ ediff-clone-buffer-for-region-comparison
 	  (quit
 	   (ediff-kill-buffer-carefully cloned-buff)))
         )
-    cloned-buff))
+      cloned-buff)))
 
 
 (defun ediff-clone-buffer-for-window-comparison (buff wind region-name)

The generated output below reflects my site's actual default config,
but the reproduction steps above work with Emacs's defaults.

Emacs  : GNU Emacs 30.1.90 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 1.15.12, Xaw scroll bars)
 of 2025-06-25
Package: Ediff 2.81.6

current state:
==============
(setq
 ediff-diff-program "diff"
 ediff-diff-options ""
 ediff-diff3-program "diff3"
 ediff-diff3-options ""
 ediff-patch-program "patch"
 ediff-patch-options "-f"
 ediff-shell "sh"
 ediff-use-faces t
 ediff-auto-refine 'on
 ediff-highlighting-style 'face
 ediff-buffer-A nil
 ediff-buffer-B nil
 ediff-control-buffer nil
 ediff-forward-word-function 'ediff-forward-word
 ediff-control-frame nil
 ediff-control-frame-parameters '((name . "Ediff") (minibuffer) (user-position . t) (vertical-scroll-bars) (menu-bar-lines . 0)
                                  (tool-bar-lines . 0) (left-fringe . 0) (right-fringe . 0) (auto-lower) (auto-raise . t) (visibility)
                                  (width . 1) (height . 1) (fullscreen) (top . 4321) (left . 3841))
 ediff-control-frame-position-function 'ediff-make-frame-position
 ediff-prefer-iconified-control-frame nil
 ediff-window-setup-function 'ediff-setup-windows-plain
 ediff-split-window-function 'split-window-horizontally
 ediff-job-name nil
 ediff-word-mode nil
 ediff-buffer-name " *ediff-message*"
 window-system 'x
 )

Message #10 received at 78897-done <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Aaron Zeng <azeng <at> janestreet.com>
Cc: kifer <at> cs.stonybrook.edu, app-emacs-dev <at> janestreet.com,
 78897-done <at> debbugs.gnu.org
Subject: Re: bug#78897: Ediff 2.81.6;
 Window restoration with ediff-before-setup-hook doesn't work for
 ediff-regions-linewise
Date: Sat, 05 Jul 2025 11:09:03 +0300

> Cc: app-emacs-dev <at> janestreet.com
> Date: Wed, 25 Jun 2025 16:40:51 -0400
> From:  Aaron Zeng via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs <at> gnu.org>
> 
> ediff-before-setup-hook's docstring suggests using it to save and
> restore the window configuration prior to invoking an Ediff command.
> Users at my site have an equivalent to the following hooks:
> 
> (defvar my-saved-window-configuration nil)
> (add-hook 'ediff-before-setup-hook
>           (lambda ()
>             (setq my-saved-window-configuration (current-window-configuration))))
> (add-hook 'ediff-quit-hook
>           (lambda ()
>             (set-window-configuration my-saved-window-configuration)
>             (setq my-saved-window-configuration nil)))
> 
> This works fine for most Ediff commands but does not work correctly
> with ediff-regions-linewise and ediff-regions-wordwise.  You can
> reproduce the behavior from emacs -Q:
> 
> 1. emacs -Q
> 2. Evaluate the above snippet
> 3. M-x ediff-regions-linewise (select an arbitrary pair of buffers and
>    regions like selecting *scratch* twice)
> 4. Press q
> 
> After quitting, the original window configuration is not restored.  In
> particular, the window is split vertically with a short window below
> the selected taller one.
> 
> I believe this is because those commands use
> ediff-clone-buffer-for-region-comparison to prompt for regions as diff
> input, and that involves adjusting the window configuration a few
> times.  The following patch seems to fix the behavior (edited to
> remove the indentation diff for brevity):

Thanks, I've now installed this on the master branch, and I'm
therefore closing this bug.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.