bug#48493: 28.0.50; quit-window doesn't work

[pillule <pillule@riseup.net>]

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martin rudalics <rudalics@gmx.at> writes:

> This is quite a weakness of the present mechanism and I think 
> you got
> it right.  To summarize your approach:
>
> - When we have to replace a buffer in a side window, that 
> window's
>   dedicated status is 'side', and some other buffer is found 
>   that was
>   shown there before (it's on the list of that window's 
>   _previous_
>   buffers) we show that other buffer in the window and make sure 
>   to
>   restore the window's dedicated status to 'side'.
>
> - Otherwise delete the window.  Deleting the window is always 
> possible
>   and we have to make sure one thing - never show in a side 
>   window a
>   buffer that has not been shown before in that window.  This 
>   rule
>   should take care of the DOOM workaround.
>
> And users who override the behavior sketched here by setting the 
> side
> window's dedicated status to t should have the window deleted 
> (since
> that is always possible).
>
> Have I got it right?

Yes.
Maybe it is a step toward implementing the `soft' dedication that 
is mentioned in the comments.
Thanks you for the explanations.

> We have to document it in the Elisp manual.

Here another draft with the info manual changes:

From what I have tested so far, there were more functions that 
needed to preserve the side dedication. I put in my modeline a 
token for the window dedication and it was quite useful to spot 
them (maybe not the clever way but worked). I also grepped into 
window.el to see if I was missing something without more success.

There is a change in the indentation of `quit-restore-window' and 
I don't know if there is convention in such cases.


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From 4327b124afd2169e218509143175d1a20f9f65ce Mon Sep 17 00:00:00 2001
From: Trust me I am a doctor <pillule@riseup.net>
Date: Tue, 8 Jun 2021 01:12:03 +0200
Subject: [PATCH] Improve handling of dedicated side flag when quitting window

Following the discussion on (Bug#48493), restore the dedicated side
flag of windows when a buffer change in the window, update the
documentation.

* doc/lispref/windows.texi
  (Buffers and Windows): mention the exception of side windows and
add a reference.
  (Buffer Display Action Alists): explicit that
`display-buffer-in-side-window' is dedicating to side by default.
  (Dedicated Windows): add the case (4) and explicit its meaning,
add a reference.
  (Displaying Buffers in Side Windows): move the
switch-to-(prev|next)-buffer paragraph into a new item to emphasize
the special meaning of dedication for side windows.

* lisp/window.el
  (set-window-buffer-start-and-point): restore side dedication.
  (switch-to-prev-buffer): corrige the return value that should be
nil instead of the same buffer in case of no changement.
  (switch-to-next-buffer): corrige the return value that should be
nil instead of the same buffer in case of no changement.
  (delete-windows-on): restore side dedication.
  (replace-buffer-in-windows): update the docstring, restore side
dedication.
  (quit-restore-window): rearrange the logic so hard dedicated windows
are eventually deleted first, restore the side dedication, try to
`switch-to-prev-buffer' before deleting a side window, fix (Bug#48367)
---
 doc/lispref/windows.texi |  58 +++++++----
 lisp/window.el           | 216 ++++++++++++++++++++++-----------------
 2 files changed, 159 insertions(+), 115 deletions(-)

diff --git a/doc/lispref/windows.texi b/doc/lispref/windows.texi
index 44656c057a..601f59e650 100644
--- a/doc/lispref/windows.texi
+++ b/doc/lispref/windows.texi
@@ -2172,12 +2172,13 @@ Buffers and Windows
 the current buffer.
 
 The replacement buffer in each window is chosen via
-@code{switch-to-prev-buffer} (@pxref{Window History}).  Any dedicated
-window displaying @var{buffer-or-name} is deleted if possible
-(@pxref{Dedicated Windows}).  If such a window is the only window on its
-frame and there are other frames on the same terminal, the frame is
-deleted as well.  If the dedicated window is the only window on the only
-frame on its terminal, the buffer is replaced anyway.
+@code{switch-to-prev-buffer} (@pxref{Window History}).  With the
+exception of side windows, any dedicated window displaying
+@var{buffer-or-name} is deleted if possible (@pxref{Dedicated
+Windows}).  If such a window is the only window on its frame and there
+are other frames on the same terminal, the frame is deleted as well.
+If the dedicated window is the only window on the only frame on its
+terminal, the buffer is replaced anyway.
 @end deffn
 
 
@@ -2994,6 +2995,8 @@ Buffer Display Action Alists
 any window it creates as dedicated to its buffer (@pxref{Dedicated
 Windows}).  It does that by calling @code{set-window-dedicated-p} with
 the chosen window as first argument and the entry's value as second.
+Side windows are by default dedicated with the value @code{side}
+((@pxref{Side Window Options and Functions}).
 
 @vindex preserve-size@r{, a buffer display action alist entry}
 @item preserve-size
@@ -4042,18 +4045,19 @@ Dedicated Windows
 
    Functions supposed to remove a buffer from a window or a window from
 a frame can behave specially when a window they operate on is dedicated.
-We will distinguish three basic cases, namely where (1) the window is
+We will distinguish four basic cases, namely where (1) the window is
 not the only window on its frame, (2) the window is the only window on
-its frame but there are other frames on the same terminal left, and (3)
-the window is the only window on the only frame on the same terminal.
+its frame but there are other frames on the same terminal left, (3)
+the window is the only window on the only frame on the same terminal,
+and (4) the dedication's value is @code{side}
+(@pxref{Displaying Buffers in Side Windows}).
 
    In particular, @code{delete-windows-on} (@pxref{Deleting Windows})
-handles case (2) by deleting the associated frame and case (3) by
-showing another buffer in that frame's only window.  The function
+handles case (2) by deleting the associated frame and case (3) and (4)
+by showing another buffer in that frame's only window.  The function
 @code{replace-buffer-in-windows} (@pxref{Buffers and Windows}) which is
 called when a buffer gets killed, deletes the window in case (1) and
 behaves like @code{delete-windows-on} otherwise.
-@c FIXME: Does replace-buffer-in-windows _delete_ a window in case (1)?
 
    When @code{bury-buffer} (@pxref{Buffer List}) operates on the
 selected window (which shows the buffer that shall be buried), it
@@ -4316,6 +4320,26 @@ Displaying Buffers in Side Windows
 middle slot.  Hence, all windows on a specific side are ordered by their
 @code{slot} value.  If unspecified, the window is located in the middle
 of the specified side.
+
+
+@item dedicated
+The dedicated flag is not reserved to this function but have a
+slightly different meaning for side windows.  They receive it upon
+creation with the value @code{side}; it serves to prevent
+@code{display-buffer} to uses these windows with others action
+functions, and it persists across invocations of @code{quit-window},
+@code{kill-buffer}, @code{previous-buffer} and @code{next-buffer}
+(@pxref{note Window History}).  In particular, these commands will
+refrain from showing, in a side window, buffers that have not been
+displayed in that window before.  They will also refrain from having a
+normal, non-side window show a buffer that has been already displayed
+in a side window.  A notable exception to the latter rule occurs when
+an application, after displaying a buffer, resets that buffer’s local
+variables.  To override these rules and always delete a side window
+with @code{quit-window} or @code{kill-buffer}, and eventually prevent
+the use of @code{previous-buffer} and @code{next-buffer}, set this
+value to @code{t} or specify a value for
+@code{display-buffer-mark-dedicated}.
 @end table
 
 If you specify the same slot on the same side for two or more different
@@ -4336,16 +4360,6 @@ Displaying Buffers in Side Windows
 action.  Note also that @code{delete-other-windows} cannot make a side
 window the only window on its frame (@pxref{Deleting Windows}).
 
-   Once set up, side windows also change the behavior of the commands
-@code{switch-to-prev-buffer} and @code{switch-to-next-buffer}
-(@pxref{Window History}).  In particular, these commands will refrain
-from showing, in a side window, buffers that have not been displayed in
-that window before.  They will also refrain from having a normal,
-non-side window show a buffer that has been already displayed in a side
-window.  A notable exception to the latter rule occurs when an
-application, after displaying a buffer, resets that buffer's local
-variables.
-
 
 @node Side Window Options and Functions
 @subsection Side Window Options and Functions
diff --git a/lisp/window.el b/lisp/window.el
index fd1c617d6b..f619372af8 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -4424,8 +4424,12 @@ set-window-buffer-start-and-point
 before was current this also makes BUFFER the current buffer."
   (setq window (window-normalize-window window t))
   (let ((selected (eq window (selected-window)))
-	(current (eq (window-buffer window) (current-buffer))))
+	(current (eq (window-buffer window) (current-buffer)))
+        (dedicated (window-dedicated-p window)))
     (set-window-buffer window buffer)
+    ;; restore the dedicated side flag
+    (when (eq dedicated 'side)
+      (set-window-dedicated-p window 'side))
     (when (and selected current)
       (set-buffer buffer))
     (when start
@@ -4559,11 +4563,11 @@ switch-to-prev-buffer
       ;; Scan WINDOW's previous buffers first, skipping entries of next
       ;; buffers.
       (dolist (entry (window-prev-buffers window))
-	(when (and (setq new-buffer (car entry))
+	(when (and (not (eq (car entry) old-buffer))
+                   (setq new-buffer (car entry))
 		   (or (buffer-live-p new-buffer)
 		       (not (setq killed-buffers
 				  (cons new-buffer killed-buffers))))
-		   (not (eq new-buffer old-buffer))
                    (or (null pred) (funcall pred new-buffer))
 		   ;; When BURY-OR-KILL is nil, avoid switching to a
 		   ;; buffer in WINDOW's next buffers list.
@@ -4726,11 +4730,11 @@ switch-to-next-buffer
       ;; Scan WINDOW's reverted previous buffers last (must not use
       ;; nreverse here!)
       (dolist (entry (reverse (window-prev-buffers window)))
-	(when (and (setq new-buffer (car entry))
+	(when (and (not (eq new-buffer (car entry)))
+                   (setq new-buffer (car entry))
 		   (or (buffer-live-p new-buffer)
 		       (not (setq killed-buffers
 				  (cons new-buffer killed-buffers))))
-		   (not (eq new-buffer old-buffer))
                    (or (null pred) (funcall pred new-buffer)))
           (if (switch-to-prev-buffer-skip-p skip window new-buffer)
 	      (setq skipped (or skipped new-buffer))
@@ -4957,9 +4961,10 @@ delete-windows-on
 	(all-frames (cond ((not frame) t) ((eq frame t) nil) (t frame))))
     (dolist (window (window-list-1 nil nil all-frames))
       (if (eq (window-buffer window) buffer)
-	  (let ((deletable (window-deletable-p window)))
+	  (let ((deletable (window-deletable-p window))
+                (dedicated (window-dedicated-p window)))
 	    (cond
-	     ((and (eq deletable 'frame) (window-dedicated-p window))
+	     ((and (eq deletable 'frame) dedicated)
 	      ;; Delete frame if and only if window is dedicated.
 	      (delete-frame (window-frame window)))
 	     ((eq deletable t)
@@ -4968,7 +4973,10 @@ delete-windows-on
 	     (t
 	      ;; In window switch to previous buffer.
 	      (set-window-dedicated-p window nil)
-	      (switch-to-prev-buffer window 'bury))))
+	      (switch-to-prev-buffer window 'bury)
+              ;; restore the dedicated side flag
+              (when (eq dedicated 'side)
+                (set-window-dedicated-p window 'side)))))
 	;; If a window doesn't show BUFFER, unrecord BUFFER in it.
 	(unrecord-window-buffer window buffer)))))
 
@@ -4977,10 +4985,10 @@ replace-buffer-in-windows
 BUFFER-OR-NAME may be a buffer or the name of an existing buffer
 and defaults to the current buffer.
 
-When a window showing BUFFER-OR-NAME is dedicated, that window is
-deleted.  If that window is the only window on its frame, the
-frame is deleted too when there are other frames left.  If there
-are no other frames left, some other buffer is displayed in that
+With the exception of side windows, when a window showing BUFFER-OR-NAME
+is dedicated, that window is deleted.  If that window is the only window
+on its frame, the frame is deleted too when there are other frames left.
+If there are no other frames left, some other buffer is displayed in that
 window.
 
 This function removes the buffer denoted by BUFFER-OR-NAME from
@@ -4989,10 +4997,14 @@ replace-buffer-in-windows
   (let ((buffer (window-normalize-buffer buffer-or-name)))
     (dolist (window (window-list-1 nil nil t))
       (if (eq (window-buffer window) buffer)
-	  (unless (window--delete window t t)
-	    ;; Switch to another buffer in window.
-	    (set-window-dedicated-p window nil)
-	    (switch-to-prev-buffer window 'kill))
+          ;; delete dedicated window that are not side windows
+          (let ((dedicated-side (eq (window-dedicated-p window) 'side)))
+            (when (or dedicated-side (not (window--delete window t t)))
+              ;; Switch to another buffer in window.
+              (set-window-dedicated-p window nil)
+              (if (switch-to-prev-buffer window 'kill)
+                  (and dedicated-side (set-window-dedicated-p window 'side))
+                (window--delete window nil 'kill))))
 	;; Unrecord BUFFER in WINDOW.
 	(unrecord-window-buffer window buffer)))))
 
@@ -5014,6 +5026,10 @@ quit-restore-window
 parameter to nil.  See Info node `(elisp) Quitting Windows' for
 more details.
 
+If WINDOW have the flag dedicated with the value t, always try to
+delete WINDOW, with the value side, restore that value when
+WINDOW is not deleted.
+
 Optional second argument BURY-OR-KILL tells how to proceed with
 the buffer of WINDOW.  The following values are handled:
 
@@ -5040,87 +5056,101 @@ quit-restore-window
                         (dolist (buf (window-prev-buffers window))
                           (unless (eq (car buf) buffer)
                             (throw 'prev-buffer (car buf))))))
+         (dedicated (window-dedicated-p window))
 	 quad entry)
-    (cond
-     ((and (not prev-buffer)
-	   (eq (nth 1 quit-restore) 'tab)
-	   (eq (nth 3 quit-restore) buffer))
-      (tab-bar-close-tab)
-      ;; If the previously selected window is still alive, select it.
-      (when (window-live-p (nth 2 quit-restore))
-	(select-window (nth 2 quit-restore))))
-     ((and (not prev-buffer)
-	   (or (eq (nth 1 quit-restore) 'frame)
-	       (and (eq (nth 1 quit-restore) 'window)
-		    ;; If the window has been created on an existing
-		    ;; frame and ended up as the sole window on that
-		    ;; frame, do not delete it (Bug#12764).
-		    (not (eq window (frame-root-window window)))))
-	   (eq (nth 3 quit-restore) buffer)
-	   ;; Delete WINDOW if possible.
-	   (window--delete window nil (eq bury-or-kill 'kill)))
-      ;; If the previously selected window is still alive, select it.
-      (when (window-live-p (nth 2 quit-restore))
-	(select-window (nth 2 quit-restore))))
-     ((and (listp (setq quad (nth 1 quit-restore)))
-	   (buffer-live-p (car quad))
-	   (eq (nth 3 quit-restore) buffer))
-      ;; Show another buffer stored in quit-restore parameter.
-      (when (and (integerp (nth 3 quad))
-		 (if (window-combined-p window)
-                     (/= (nth 3 quad) (window-total-height window))
-                   (/= (nth 3 quad) (window-total-width window))))
-	;; Try to resize WINDOW to its old height but don't signal an
-	;; error.
-	(condition-case nil
-	    (window-resize
-             window
-             (- (nth 3 quad) (if (window-combined-p window)
-                                 (window-total-height window)
-                               (window-total-width window)))
-             (window-combined-p window t))
-	  (error nil)))
-      (set-window-dedicated-p window nil)
-      ;; Restore WINDOW's previous buffer, start and point position.
-      (set-window-buffer-start-and-point
-       window (nth 0 quad) (nth 1 quad) (nth 2 quad))
-      ;; Deal with the buffer we just removed from WINDOW.
-      (setq entry (and (eq bury-or-kill 'append)
-		       (assq buffer (window-prev-buffers window))))
-      (when bury-or-kill
-	;; Remove buffer from WINDOW's previous and next buffers.
-	(set-window-prev-buffers
-	 window (assq-delete-all buffer (window-prev-buffers window)))
-	(set-window-next-buffers
-	 window (delq buffer (window-next-buffers window))))
-      (when entry
-	;; Append old buffer's entry to list of WINDOW's previous
-	;; buffers so it's less likely to get switched to soon but
-	;; `display-buffer-in-previous-window' can nevertheless find it.
-	(set-window-prev-buffers
-	 window (append (window-prev-buffers window) (list entry))))
-      ;; Reset the quit-restore parameter.
-      (set-window-parameter window 'quit-restore nil)
-      ;; Select old window.
-      (when (window-live-p (nth 2 quit-restore))
-	(select-window (nth 2 quit-restore))))
-     (t
-      ;; Show some other buffer in WINDOW and reset the quit-restore
-      ;; parameter.
-      (set-window-parameter window 'quit-restore nil)
-      ;; Make sure that WINDOW is no more dedicated.
-      (set-window-dedicated-p window nil)
-      (unless (switch-to-prev-buffer window bury-or-kill)
-        ;; Delete WINDOW if there is no previous buffer (Bug#48367).
-        (window--delete window nil (eq bury-or-kill 'kill)))))
+    (or ;; first try to delete dedicated windows that are not side windows
+     (and dedicated (not (eq dedicated 'side))
+          (window--delete window 'dedicated (eq bury-or-kill 'kill)))
+     (cond
+       ((and (not prev-buffer)
+             (eq (nth 1 quit-restore) 'tab)
+             (eq (nth 3 quit-restore) buffer))
+        (tab-bar-close-tab)
+        ;; If the previously selected window is still alive, select it.
+        (when (window-live-p (nth 2 quit-restore))
+          (select-window (nth 2 quit-restore))))
+       ((and (not prev-buffer)
+             (or (eq (nth 1 quit-restore) 'frame)
+                 (and (eq (nth 1 quit-restore) 'window)
+                      ;; If the window has been created on an existing
+                      ;; frame and ended up as the sole window on that
+                      ;; frame, do not delete it (Bug#12764).
+                      (not (eq window (frame-root-window window)))))
+             (eq (nth 3 quit-restore) buffer)
+             ;; Delete WINDOW if possible.
+             (window--delete window nil (eq bury-or-kill 'kill)))
+        ;; If the previously selected window is still alive, select it.
+        (when (window-live-p (nth 2 quit-restore))
+          (select-window (nth 2 quit-restore))))
+       ((and (listp (setq quad (nth 1 quit-restore)))
+             (buffer-live-p (car quad))
+             (eq (nth 3 quit-restore) buffer))
+        ;; Show another buffer stored in quit-restore parameter.
+        (when (and (integerp (nth 3 quad))
+                   (if (window-combined-p window)
+                       (/= (nth 3 quad) (window-total-height window))
+                     (/= (nth 3 quad) (window-total-width window))))
+          ;; Try to resize WINDOW to its old height but don't signal an
+          ;; error.
+          (condition-case nil
+              (window-resize
+               window
+               (- (nth 3 quad) (if (window-combined-p window)
+                                   (window-total-height window)
+                                 (window-total-width window)))
+               (window-combined-p window t))
+            (error nil)))
+        (set-window-dedicated-p window nil)
+        ;; Restore WINDOW's previous buffer, start and point position.
+        (set-window-buffer-start-and-point
+         window (nth 0 quad) (nth 1 quad) (nth 2 quad))
+        ;; and restore the dedicated side flag
+        (when (eq dedicated 'side) (set-window-dedicated-p window 'side))
+        ;; Deal with the buffer we just removed from WINDOW.
+        (setq entry (and (eq bury-or-kill 'append)
+                         (assq buffer (window-prev-buffers window))))
+        (when bury-or-kill
+          ;; Remove buffer from WINDOW's previous and next buffers.
+          (set-window-prev-buffers
+           window (assq-delete-all buffer (window-prev-buffers window)))
+          (set-window-next-buffers
+           window (delq buffer (window-next-buffers window))))
+        (when entry
+          ;; Append old buffer's entry to list of WINDOW's previous
+          ;; buffers so it's less likely to get switched to soon but
+          ;; `display-buffer-in-previous-window' can nevertheless find it.
+          (set-window-prev-buffers
+           window (append (window-prev-buffers window) (list entry))))
+        ;; Reset the quit-restore parameter.
+        (set-window-parameter window 'quit-restore nil)
+        ;; Select old window.
+        (when (window-live-p (nth 2 quit-restore))
+          (select-window (nth 2 quit-restore))))
+       (t
+        ;; Show some other buffer in WINDOW and reset the quit-restore
+        ;; parameter.
+        (set-window-parameter window 'quit-restore nil)
+        ;; Make sure that WINDOW is no more dedicated.
+        (set-window-dedicated-p window nil)
+        (if (and prev-buffer (eq dedicated 'side)) ;;  (Bug#48367)
+            ;; If a previous buffer exists, try to switch to it.  If that
+            ;; fails for whatever reason, try to delete the window.
+            (if (switch-to-prev-buffer window bury-or-kill)
+                (set-window-dedicated-p window 'side)
+              (window--delete window nil (eq bury-or-kill 'kill)))
+          ;; If no previous buffer exists, try to delete the window.  If
+          ;; that fails for whatever reason, try to switch to some other
+          ;; buffer.
+          (unless (window--delete window nil (eq bury-or-kill 'kill))
+            (switch-to-prev-buffer window bury-or-kill))))))
 
     ;; Deal with the buffer.
     (cond
-     ((not (buffer-live-p buffer)))
-     ((eq bury-or-kill 'kill)
-      (kill-buffer buffer))
-     (bury-or-kill
-      (bury-buffer-internal buffer)))))
+      ((not (buffer-live-p buffer)))
+      ((eq bury-or-kill 'kill)
+       (kill-buffer buffer))
+      (bury-or-kill
+       (bury-buffer-internal buffer)))))
 
 (defun quit-window (&optional kill window)
   "Quit WINDOW and bury its buffer.
-- 
2.20.1


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