bug#20472: 24.4; Cannot switch buffers in a dedicated window - report this error earlier

bug#20472: 24.4; Cannot switch buffers in a dedicated window - report this error earlier

[Ed Avis]

Sometimes Emacs creates a small window such as *log-edit-files*.
If you go to that window and do C-x b, you enter the name of the buffer
to switch to as usual, but then see the error

    Cannot switch buffers in a dedicated window

This error message should appear earlier, as soon as C-x b is given.
Emacs should not ask you to type in the new buffer name before it tells
you that switching buffers is not allowed.



In GNU Emacs 24.4.1 (x86_64-redhat-linux-gnu, GTK+ Version 3.10.9)
 of 2014-11-03 on wcl-linux04.wcl.local
Configured using:
 `configure --build=x86_64-redhat-linux-gnu
 --host=x86_64-redhat-linux-gnu --program-prefix=
 --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr
 --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
 --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
 --libexecdir=/usr/libexec --localstatedir=/var
 --sharedstatedir=/var/lib --mandir=/usr/share/man
 --infodir=/usr/share/info --with-dbus --with-gif --with-jpeg --with-png
 --with-rsvg --with-tiff --with-xft --with-xpm --with-x-toolkit=gtk3
 --with-gpm=no build_alias=x86_64-redhat-linux-gnu
 host_alias=x86_64-redhat-linux-gnu 'CFLAGS=-DMAIL_USE_LOCKF -O2 -g
 -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions
 -fstack-protector-strong --param=ssp-buffer-size=4
 -grecord-gcc-switches -m64 -mtune=generic' 'LDFLAGS=-Wl,-z,relro ''

Important settings:
  value of $LC_COLLATE: C
  value of $LC_CTYPE: en_GB.UTF-8
  value of $LC_MESSAGES: en_GB.UTF-8
  value of $LC_MONETARY: en_GB.UTF-8
  value of $LC_NUMERIC: en_GB.UTF-8
  value of $LC_TIME: en_GB.UTF-8
  value of $LANG: en_GB.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  diff-auto-refine-mode: t
  shell-dirtrack-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
SPC c g TAB C-a C-k C-x b G u TAB RET . TAB RET C-x 
v = ESC [ 6 ~ ESC [ 5 ~ C-x o C-x o C-x v = C-x v v 
R e d u c e SPC DEL d SPC f i l l i n g SPC f r o m 
SPC 1 0 0 SPC t o SPC 3 0 SPC d a t DEL y s SPC f o 
r SPC s o m e SPC m o n t h l y SPC s t r a t e g i 
e s . RET T h i s SPC c a n SPC b e SPC d o n e SPC 
n o w SPC t h e SPC h DEL g a p s SPC i n SPC C o n 
s e n e s u s DEL DEL DEL DEL DEL DEL DEL DEL DEL DEL 
C-x o C-x b b u TAB RET C-g C-g C-g C-x b b u TAB RET 
C-g C-g C-g C-x o C-x b b u TAB C-g C-x o C-x o C-x 
b * l o TAB g - e TAB C-g C-x b C-g C-x o C-x o C-x 
o ESC x C-g C-x b f a RET C-x b g g RET C-g C-g C-x 
o C-x b g g RET C a n n o t SPC s w i t c h SPC b u 
f f e r s SPC i n SPC a SPC d e d i c a t e d SPC w 
i n d o w C-x o C-x o C-x o C-@ C-a ESC w ESC x r e 
p o r SPC e SPC b SPC RET

Recent messages:
Press C-c C-c when you are done editing.
Enter a change comment.  Type C-c C-c when done
user-error: Cannot switch buffers in a dedicated window
Quit [3 times]
user-error: Cannot switch buffers in a dedicated window
Quit [4 times]
Making completion list...
Quit [3 times]
user-error: Cannot switch buffers in a dedicated window [2 times]
Quit [2 times]

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug sendmail warnings dired-aux vc-bzr
vc-sccs vc-svn vc-cvs vc-rcs mule-util macros smerge-mode rect novice
edmacro kmacro etags log-view nxml-uchnm rng-xsd xsd-regexp rng-cmpct
rng-nxml rng-valid rng-loc rng-uri rng-parse nxml-parse rng-match rng-dt
rng-util rng-pttrn nxml-ns nxml-mode nxml-outln nxml-rap nxml-util
nxml-glyph nxml-enc xmltok sql view diff-mode vc vc-dispatcher tabify
imenu man sh-script smie executable pcmpl-rpm dabbrev ffap thingatpt
url-parse auth-source eieio eieio-core gnus-util password-cache url-vars
nroff-mode help-mode dired misearch multi-isearch vc-git cus-edit
wid-edit cus-start cus-load perl-mode pcmpl-unix xterm time-date
log-edit easy-mmode message format-spec rfc822 mml mml-sec mm-decode
mm-bodies mm-encode mail-parse rfc2231 rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mailabbrev mail-utils gmm-utils mailheader pcvs-util
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cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs zoom-frm frame-cmds
frame-fns cl-macs avoid cl gv cl-loaddefs cl-lib compile shell pcomplete
comint ring ansi-color tooltip electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote make-network-process dbusbind
gfilenotify dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 1254638 183358)
 (symbols 48 29960 0)
 (miscs 40 760 4364)
 (strings 32 63447 13092)
 (string-bytes 1 3117305)
 (vectors 16 32306)
 (vector-slots 8 1444102 177426)
 (floats 8 560 1031)
 (intervals 56 189950 392)
 (buffers 960 151)
 (heap 1024 93365 1704))

-- 
Ed Avis <eda@waniasset.com>
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bug#20472: 24.4; Cannot switch buffers in a dedicated window - report this error earlier

[martin rudalics]

 > Sometimes Emacs creates a small window such as *log-edit-files*.
 > If you go to that window and do C-x b, you enter the name of the buffer
 > to switch to as usual, but then see the error
 >
 >      Cannot switch buffers in a dedicated window
 >
 > This error message should appear earlier, as soon as C-x b is given.
 > Emacs should not ask you to type in the new buffer name before it tells
 > you that switching buffers is not allowed.

Indeed.  Unless someone has a better idea I'll install something like the below.

martin


--- a/lisp/window.el
+++ b/lisp/window.el
@@ -6916,7 +6916,13 @@ window.

  Return the buffer switched to."
    (interactive
-   (list (read-buffer-to-switch "Switch to buffer: ") nil 'force-same-window))
+   (cond
+    ((eq (window-dedicated-p) t)
+     (user-error "Cannot switch buffers in a dedicated window"))
+    ((window-minibuffer-p)
+     (user-error "Cannot switch buffers in minibuffer window"))
+    (t
+     (list (read-buffer-to-switch "Switch to buffer: ") nil 'force-same-window))))
    (let ((buffer (window-normalize-buffer-to-switch-to buffer-or-name)))
      (cond
       ;; Don't call set-window-buffer if it's not needed since it

bug#20472: 24.4; Cannot switch buffers in a dedicated window - report this error earlier

[Stefan Monnier]

>> Cannot switch buffers in a dedicated window
>> 
>> This error message should appear earlier, as soon as C-x b is given.
>> Emacs should not ask you to type in the new buffer name before it tells
>> you that switching buffers is not allowed.

> Indeed.  Unless someone has a better idea I'll install something like
> the below.

An alternative would be to make C-x b use another window in such a case.
I.e. remove the `force-same-window' argument (I think that would make
sense at least for the window-minibuffer-p case).  An other alternative
would be to un-dedicate the window (only after prompting the user, tho).


        Stefan

bug#20472: 24.4; Cannot switch buffers in a dedicated window - report this error earlier

[martin rudalics]

[-- Attachment #1: Type: text/plain, Size: 467 bytes --]

 > An alternative would be to make C-x b use another window in such a case.
 > I.e. remove the `force-same-window' argument (I think that would make
 > sense at least for the window-minibuffer-p case).

Agreed.

 > An other alternative
 > would be to un-dedicate the window (only after prompting the user, tho).

Patch attached.  In the *log-edit-files* case we could additionally make
the window weakly dedicated in order to avoid this problem all together.

martin

[-- Attachment #2: switch-to-buffer.patch --]
[-- Type: text/plain, Size: 2479 bytes --]

--- a/lisp/window.el
+++ b/lisp/window.el
@@ -6887,10 +6887,13 @@ WARNING: This is NOT the way to work on another buffer temporarily
 within a Lisp program!  Use `set-buffer' instead.  That avoids
 messing with the window-buffer correspondences.

-If the selected window cannot display the specified
-buffer (e.g. if it is a minibuffer window or strongly dedicated
-to another buffer), call `pop-to-buffer' to select the buffer in
-another window.
+If the selected window cannot display the specified buffer
+because it is a minibuffer window or strongly dedicated to
+another buffer, call `pop-to-buffer' to select the buffer in
+another window.  But if the optional argument FORCE-SAME-WINDOW
+is non-nil and the selected window is strongly dedicated to its
+buffer, prompt the user whether to undedicate the selected window
+first.

 If called interactively, read the buffer name using the
 minibuffer.  The variable `confirm-nonexistent-file-or-buffer'
@@ -6906,10 +6909,6 @@ If optional argument NORECORD is non-nil, do not put the buffer
 at the front of the buffer list, and do not make the window
 displaying it the most recently selected one.

-If optional argument FORCE-SAME-WINDOW is non-nil, the buffer
-must be displayed in the selected window; if that is impossible,
-signal an error rather than calling `pop-to-buffer'.
-
 The option `switch-to-buffer-preserve-window-point' can be used
 to make the buffer appear at its last position in the selected
 window.
@@ -6923,13 +6922,14 @@ Return the buffer switched to."
      ;; might signal an error (e.g. if the window is dedicated).
      ((eq buffer (window-buffer)))
      ((window-minibuffer-p)
-      (if force-same-window
-          (user-error "Cannot switch buffers in minibuffer window")
-        (pop-to-buffer buffer norecord)))
-     ((eq (window-dedicated-p) t)
-      (if force-same-window
-          (user-error "Cannot switch buffers in a dedicated window")
-        (pop-to-buffer buffer norecord)))
+      (pop-to-buffer buffer norecord))
+     ((and (eq (window-dedicated-p) t)
+           (or (not force-same-window)
+               (not (y-or-n-p
+                     (format "Window is dedicated to %s; undedicate it"
+                             (window-buffer))))
+               (set-window-dedicated-p nil nil)))
+      (pop-to-buffer buffer norecord))
      (t
       (let* ((entry (assq buffer (window-prev-buffers)))
 	     (displayed (and (eq switch-to-buffer-preserve-window-point

bug#20472: 24.4; Cannot switch buffers in a dedicated window - report this error earlier

[Stefan Monnier]

> Patch attached.

AFAICT, the patch affects the switch-to-buffer function's behavior,
whereas I only want to affect the command bound to C-x b.

IOW, I don't want to affect non-interactive calls.


        Stefan

bug#20472: 24.4; Cannot switch buffers in a dedicated window - report this error earlier

[martin rudalics]

[-- Attachment #1: Type: text/plain, Size: 215 bytes --]

 > AFAICT, the patch affects the switch-to-buffer function's behavior,
 > whereas I only want to affect the command bound to C-x b.
 >
 > IOW, I don't want to affect non-interactive calls.

At your service.

martin

[-- Attachment #2: switch-to-buffer.diff --]
[-- Type: text/plain, Size: 1628 bytes --]

--- a/lisp/window.el
+++ b/lisp/window.el
@@ -6887,10 +6887,11 @@ WARNING: This is NOT the way to work on another buffer temporarily
 within a Lisp program!  Use `set-buffer' instead.  That avoids
 messing with the window-buffer correspondences.

-If the selected window cannot display the specified
-buffer (e.g. if it is a minibuffer window or strongly dedicated
-to another buffer), call `pop-to-buffer' to select the buffer in
-another window.
+If the selected window cannot display the specified buffer
+because it is a minibuffer window or strongly dedicated to
+another buffer, call `pop-to-buffer' to select the buffer in
+another window.  In interactive use offer to undedicate the
+selected window before.

 If called interactively, read the buffer name using the
 minibuffer.  The variable `confirm-nonexistent-file-or-buffer'
@@ -6916,7 +6917,15 @@ window.

 Return the buffer switched to."
   (interactive
-   (list (read-buffer-to-switch "Switch to buffer: ") nil 'force-same-window))
+   (let ((force-same-window
+          (and (not (window-minibuffer-p))
+               (or (not (eq (window-dedicated-p) t))
+                   (and (y-or-n-p
+                         (format "Window is dedicated to %s; undedicate it"
+                                 (window-buffer)))
+                        (or (set-window-dedicated-p nil nil) t)))
+               'force-same-window)))
+     (list (read-buffer-to-switch "Switch to buffer: ") nil force-same-window)))
   (let ((buffer (window-normalize-buffer-to-switch-to buffer-or-name)))
     (cond
      ;; Don't call set-window-buffer if it's not needed since it

bug#20472: 24.4; Cannot switch buffers in a dedicated window - report this error earlier

[Stefan Monnier]

> At your service.

Looks OK, thanks (I'm not 100% sure prompting will turn out to be a good
idea, but we can give it a try)


        Stefan


> --- a/lisp/window.el
> +++ b/lisp/window.el
> @@ -6887,10 +6887,11 @@ WARNING: This is NOT the way to work on another buffer temporarily
>  within a Lisp program!  Use `set-buffer' instead.  That avoids
>  messing with the window-buffer correspondences.

> -If the selected window cannot display the specified
> -buffer (e.g. if it is a minibuffer window or strongly dedicated
> -to another buffer), call `pop-to-buffer' to select the buffer in
> -another window.
> +If the selected window cannot display the specified buffer
> +because it is a minibuffer window or strongly dedicated to
> +another buffer, call `pop-to-buffer' to select the buffer in
> +another window.  In interactive use offer to undedicate the
> +selected window before.

>  If called interactively, read the buffer name using the
>  minibuffer.  The variable `confirm-nonexistent-file-or-buffer'
> @@ -6916,7 +6917,15 @@ window.

>  Return the buffer switched to."
>    (interactive
> -   (list (read-buffer-to-switch "Switch to buffer: ") nil 'force-same-window))
> +   (let ((force-same-window
> +          (and (not (window-minibuffer-p))
> +               (or (not (eq (window-dedicated-p) t))
> +                   (and (y-or-n-p
> +                         (format "Window is dedicated to %s; undedicate it"
> +                                 (window-buffer)))
> +                        (or (set-window-dedicated-p nil nil) t)))
> +               'force-same-window)))
> +     (list (read-buffer-to-switch "Switch to buffer: ") nil force-same-window)))
>    (let ((buffer (window-normalize-buffer-to-switch-to buffer-or-name)))
>      (cond
>       ;; Don't call set-window-buffer if it's not needed since it

bug#20472: 24.4; Cannot switch buffers in a dedicated window - report this error earlier

[martin rudalics]

[-- Attachment #1: Type: text/plain, Size: 147 bytes --]

 > (I'm not 100% sure prompting will turn out to be a good
 > idea, but we can give it a try)

Then let's make it customizable right away.

martin

[-- Attachment #2: switch-to-buffer-in-dedicated-window.diff --]
[-- Type: text/plain, Size: 3773 bytes --]

--- a/lisp/window.el
+++ b/lisp/window.el
@@ -6880,6 +6880,33 @@ the selected window or never appeared in it before, or if
   :group 'windows
   :version "24.3")

+(defcustom switch-to-buffer-in-dedicated-window nil
+  "Allow switching to buffer in dedicated window.
+If non-nil, allow `switch-to-buffer' to proceed when called
+interactively and the selected window is strongly dedicated to
+its buffer.
+
+The following values are recognized:
+
+nil - disallow switching; signal an error
+
+prompt - prompt user whether to allow switching
+
+pop - perform `pop-to-buffer' instead
+
+t - undedicate selected window and switch
+
+When called non-interactively, `switch-to-buffer' always signals
+an error when the selected window is dedicated to its buffer and
+FORCE-SAME-WINDOW is non-nil."
+  :type '(choice
+	  (const :tag "Disallow" nil)
+	  (const :tag "Prompt" prompt)
+	  (const :tag "Pop" pop)
+	  (const :tag "Allow" t))
+  :group 'windows
+  :version "25.1")
+
 (defun switch-to-buffer (buffer-or-name &optional norecord force-same-window)
   "Display buffer BUFFER-OR-NAME in the selected window.

@@ -6887,10 +6914,12 @@ WARNING: This is NOT the way to work on another buffer temporarily
 within a Lisp program!  Use `set-buffer' instead.  That avoids
 messing with the window-buffer correspondences.

-If the selected window cannot display the specified
-buffer (e.g. if it is a minibuffer window or strongly dedicated
-to another buffer), call `pop-to-buffer' to select the buffer in
-another window.
+If the selected window cannot display the specified buffer
+because it is a minibuffer window or strongly dedicated to
+another buffer, call `pop-to-buffer' to select the buffer in
+another window.  In interactive use, if the selected window is
+dedicated to its buffer `switch-to-buffer-in-dedicated-window'
+specifies how to proceed.

 If called interactively, read the buffer name using the
 minibuffer.  The variable `confirm-nonexistent-file-or-buffer'
@@ -6907,8 +6936,9 @@ at the front of the buffer list, and do not make the window
 displaying it the most recently selected one.

 If optional argument FORCE-SAME-WINDOW is non-nil, the buffer
-must be displayed in the selected window; if that is impossible,
-signal an error rather than calling `pop-to-buffer'.
+must be displayed in the selected window when called
+non-interactively; if that is impossible, signal an error rather
+than calling `pop-to-buffer'.

 The option `switch-to-buffer-preserve-window-point' can be used
 to make the buffer appear at its last position in the selected
@@ -6916,7 +6946,25 @@ window.

 Return the buffer switched to."
   (interactive
-   (list (read-buffer-to-switch "Switch to buffer: ") nil 'force-same-window))
+   (let ((force-same-window
+          (cond
+           ((window-minibuffer-p) nil)
+           ((not (eq (window-dedicated-p) t)) 'force-same-window)
+           ((pcase switch-to-buffer-in-dedicated-window
+              (`nil (user-error
+                     "Cannot switch buffers in a dedicated window"))
+              (`prompt
+               (if (y-or-n-p
+                    (format "Window is dedicated to %s; undedicate it"
+                            (window-buffer)))
+                   (progn
+                     (set-window-dedicated-p nil nil)
+                     'force-same-window)
+                 (user-error
+                  "Cannot switch buffers in a dedicated window")))
+              (`pop nil)
+              (_ (set-window-dedicated-p nil nil) 'force-same-window))))))
+     (list (read-buffer-to-switch "Switch to buffer: ") nil force-same-window)))
   (let ((buffer (window-normalize-buffer-to-switch-to buffer-or-name)))
     (cond
      ;; Don't call set-window-buffer if it's not needed since it

bug#20472: 24.4; Cannot switch buffers in a dedicated window - report this error earlier

[martin rudalics]

> Then let's make it customizable right away.

Installed with commit f743819..31d58d4 on trunk/master.  Bug closed.

Thanks, martin