Subject: bug#67993: Selecting buffer automatically

From: Juri Linkov <[email-masked]>
Date: Sun, 14 Jan 2024 20:48:07 +0200

>> But actually the customization for "1" doesn't affect popping to "2"
>> because pop-to-buffer still selects windows and creates such layout:
>>
>>    *scratch*
>>    Buffer "1"
>>    Buffer "2"
>>
>> Only post-command-hook selects the original window afterwards
>> instead of leaving the buffer "2" selected.
>
> And if the customization for "2" meant to select the window, the final
> outcome will depend on whichever (de-)selection comes last in the
> 'post-command-hook'.  You should at least document that in the manual.
> It looks pretty fragile to me.

A practical use of this feature is for commands that display a single buffer
that is an overwhelming majority of the commands.

However, the name 'select-window' would be too confusing for users
because based on such name they will expect that it will select
the window immediately after it's displayed.

Therefore I propose to rename it to the less ambiguous name
'post-command-select-window'.  Of course it should be documented in
any case, but this will help the users who never read the documentation.

Ok, here is a complete patch with the documentation:

diff --git a/doc/lispref/windows.texi b/doc/lispref/windows.texi
index 93b25cbe67f..ecb1df82eba 100644
--- a/doc/lispref/windows.texi
+++ b/doc/lispref/windows.texi
@@ -3344,6 +3344,15 @@ Buffer Display Action Alists
 the entries @code{window-height}, @code{window-width} and
 @code{preserve-size} are applied that could resize the window to fit
 it to the inserted contents.
+
+@vindex post-command-select-window@r{, a buffer display action alist entry}
+@item post-command-select-window
+If the value is non-@code{nil}, the buffer displayed by @code{display-buffer}
+is selected after the current command is executed that runs the hook
+@code{post-command-hook} (@pxref{Command Overview}).
+If the value is @code{nil}, the buffer selected by such functions as
+@code{pop-to-buffer} is deselected, and the window that was previously
+selected before calling @code{display-buffer} remains selected.
 @end table
 
 By convention, the entries @code{window-height}, @code{window-width}
diff --git a/lisp/window.el b/lisp/window.el
index 23977691f50..b37502203b1 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -7798,6 +7803,13 @@ display-buffer
     and `preserve-size' are applied.  The function is supposed
     to fill the window body with some contents that might depend
     on dimensions of the displayed window.
+ `post-command-select-window' -- A non-nil value means that after the
+    current command is executed and the hook `post-command-hook' is called,
+    the window displayed by this function will be selected.  A nil value
+    means that if functions like `pop-to-buffer' selected another window,
+    at the end of this command that window will be deselected, and the
+    window that was selected before calling this function will remain
+    selected.
 
 The entries `window-height', `window-width', `window-size' and
 `preserve-size' are applied only when the window used for
@@ -7853,6 +7865,17 @@ display-buffer
       (while (and functions (not window))
         (setq window (funcall (car functions) buffer alist)
               functions (cdr functions)))
+      (when-let ((select (assq 'post-command-select-window alist)))
+        (letrec ((old-selected-window (selected-window))
+                 (postfun
+                  (lambda ()
+                    (if (cdr select)
+                        (when (window-live-p window)
+                          (select-window window))
+                      (when (window-live-p old-selected-window)
+                        (select-window old-selected-window)))
+                    (remove-hook 'post-command-hook postfun))))
+          (add-hook 'post-command-hook postfun)))
       (and (windowp window) window))))
 
 (defun display-buffer-other-frame (buffer)