GNU bug report logs - #76911
dedicated side windows lose their dedication upon reuse

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From: martin rudalics <rudalics <at> gmx.at>
To: Daniel Colascione <dancol <at> dancol.org>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 76911 <at> debbugs.gnu.org
Subject: bug#76911: dedicated side windows lose their dedication upon reuse
Date: Tue, 18 Mar 2025 10:02:34 +0100

>> So a dedicated flag that does not equal 'side' might cause the problem
>> here.  If it persists, I can write some code for 'display-buffer' so we
>> can find the offender.
>
> But I want the strong dedication semantics. Specifically, I'm looking
> for something like an omnipresent always available panel I can summon
> and dismiss any time with a simple keybinding. I also have facilities
> for cycling its size and extracting the omnipresent thing into a
> conventional window temporarily. I want not only strong dedication,
> but also no-other-window and no-delete-other-windows, which I
> set. Modulo bugs, it all seems to work.

You might be asking a bit too much here: The side windows mechanism does
its own handling of dedicatedness which means that if you specify
'display-buffer-in-side-window' for a buffer-2 and the window at that
slot is strongly dedicated to buffer-1, buffer-2 will be still displayed
in that window.  There's no other way because I cannot display buffer-2
reasonably anywhere else.

BTW why do you set 'no-delete-other-windows' for a side window?  You
cannot avoid an error when incidentally doing C-x 5 1 in it I suppose.

> For finding those bugs, maybe we need a history of recent window
> changes we can examine after something has gone wrong. Just today I
> got into a weird state in which I had two side windows with the same
> slot and have no idea how I got into that state or how I'd repro.

As a matter of fact, this should never happen.  You could try running
Emacs with the patch below - it might help to detect such a situation.

martin

diff --git a/lisp/window.el b/lisp/window.el
index 1e8f4e323bc..dd7a463aa3b 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -7824,6 +7824,12 @@ window--display-buffer
         (dolist (parameter parameters)
           (set-window-parameter
            window (car parameter) (cdr parameter)))))
+    (with-current-buffer (get-buffer-create "*display-buffer-history*")
+      (goto-char (point-max))
+      (insert (format " window: %s" window)
+	      (format " [%s]" type)
+	      (format " alist: %s" alist)
+	      (format " parameters: %s\n" (window-parameters window))))
     window))

 (defun window--maybe-raise-frame (frame)
@@ -8220,6 +8226,9 @@ display-buffer
 	(split-window-keep-point t)
 	;; Handle the old form of the first argument.
 	(inhibit-same-window (and action (not (listp action)))))
+    (with-current-buffer (get-buffer-create "*display-buffer-history*")
+      (goto-char (point-max))
+      (insert (format "buffer: %s" buffer) (format " action: %s\n" action)))
     (unless (listp action) (setq action nil))
     (let* ((user-action
             (display-buffer-assq-regexp

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