bug#70949: display-buffer-choose-some-window

[Juri Linkov <juri@linkov.net>]

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Addressing the request in help-gnu-emacs quoted below:

>> When cycling through, say, a rgrep result buffer with n
>> (next-error-no-select) and p (previous-error-no-select), file results
>> are displayed in every open window, with the exception of the window
>> containing the rgrep results themselves.
>>
>> I'd rather have file results remain in just one window so that I can use
>> other buffers while still viewing search results. Is this possible?
>>
>> How would I go about this? Are there any better options?
>
> The problem is that the first thing that
> 'display-buffer-use-some-window' tries to do
> is to find the least recently used window
> with 'display-buffer--lru-window'.
>
> I think this behavior should be customizable with a new option,
> so that you could prefer always to use
> the most recently used window.

here is a patch that adds such option that allows to customize
what window display-buffer-use-some-window should prefer:


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diff --git a/lisp/window.el b/lisp/window.el
index 8feeba0d83e..d34e369167e 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -8721,6 +8726,22 @@ display-buffer--lru-window
 	      (setq best-window window))))))
     (or best-window second-best-window)))
 
+(defcustom display-buffer-choose-some-window 'lru
+  "How to choose an existing window.
+This defines a strategy of choosing some window
+by `display-buffer-use-some-window'.
+
+The possible choices are `lru' (the default) to select the least recently
+used window on that frame, and `mru' to select the most recently used
+window on that frame.  When a function, it takes two arguments: a buffer
+and an alist, and should return the window where to display the buffer."
+  :type '(choice (const :tag "Least recently used" lru)
+                 (const :tag "Most recently used" mru)
+                 (function :tag "Custom function"))
+  :group 'windows
+  :group 'frames
+  :version "30.1")
+
 (defun display-buffer-use-some-window (buffer alist)
   "Display BUFFER in an existing window.
 Search for a usable window, set that window to the buffer, and
@@ -8743,11 +8764,17 @@ display-buffer-use-some-window
 		    (window--frame-usable-p (last-nonminibuffer-frame))))
 	 (window
 	  ;; Reuse an existing window.
-	  (or (display-buffer--lru-window
-               ;; If ALIST specifies 'lru-frames' or 'window-min-width'
-               ;; let them prevail.
-               (append alist `((lru-frames . ,frame)
-                               (window-min-width . full-width))))
+	  (or (cond
+               ((eq display-buffer-choose-some-window 'lru)
+                (display-buffer--lru-window
+                 ;; If ALIST specifies 'lru-frames' or 'window-min-width'
+                 ;; let them prevail.
+                 (append alist `((lru-frames . ,frame)
+                                 (window-min-width . full-width)))))
+               ((eq display-buffer-choose-some-window 'mru)
+                (get-mru-window nil nil t))
+               ((functionp display-buffer-choose-some-window)
+                (funcall display-buffer-choose-some-window buffer alist)))
 	      (let ((window (get-buffer-window buffer 'visible)))
 		(unless (and not-this-window
 			     (eq window (selected-window)))