bug#52491: 28.0.90; Regression in window deletion with minibuffer

[Juri Linkov <juri@linkov.net>]

emacs-28 -Q

 M-x	    ;; execute-extended-command
 <tab>	    ;; minibuffer-complete
 <kp-prior> ;; switch-to-completions
 q	    ;; quit-window

Point moves to the *scratch* buffer.  This is a regression.
In emacs-27 it moved to the minibuffer.

The problem is that delete-window now uses get-mru-window
to get the window to select after deleting the completions window.
But get-mru-window ignores the minibuffer window.
This could be fixed by:

diff --git a/lisp/window.el b/lisp/window.el
index 0f17bb28b4..507eaab705 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -2556,7 +2556,7 @@ get-mru-window
 Any other value of ALL-FRAMES means consider all windows on the
 selected frame and no others."
    (let (best-window best-time time)
-    (dolist (window (window-list-1 nil 'nomini all-frames))
+    (dolist (window (window-list-1 nil nil all-frames))
       (setq time (window-use-time window))
       (when (and (or dedicated (not (window-dedicated-p window)))
 		 (or (not not-selected) (not (eq window (selected-window))))

Maybe better to add a new argument to get-mru-window
and pass it down to window-list-1.

This problem exists for the default value 'mru' of
delete-window-choose-selected.  When its value is customized
to 'pos' then the *scratch* buffer is selected too,
but for a different reason.  In this case, the *scratch* buffer
is selected instead of the minibuffer because frame coordinates
of point that was previously in the completions window
now belongs to the window of the *scratch* buffer
that now takes screen space previously used by completions.
To prevent this, maybe completion-setup-function should set
buffer-local delete-window-choose-selected to 'mru'
in the completions buffer:

diff --git a/lisp/simple.el b/lisp/simple.el
index 0a58297bd2..08932c689a 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -9256,6 +9278,7 @@ completion-setup-function
         (setq-local completion-base-position base-position)
         (setq-local completion-list-insert-choice-function insert-fun))
       (setq-local completion-reference-buffer mainbuf)
+      (setq-local delete-window-choose-selected 'mru)
       (if base-dir (setq default-directory base-dir))
       (when completion-tab-width
         (setq tab-width completion-tab-width))
diff --git a/lisp/window.el b/lisp/window.el
index 0f17bb28b4..507eaab705 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -4205,6 +4205,7 @@ delete-window
   (let* ((frame (window-frame window))
 	 (function (window-parameter window 'delete-window))
 	 (parent (window-parent window))
+	 (choose-selected delete-window-choose-selected)
 	 atom-root)
     (window--check frame)
     (catch 'done
@@ -4255,7 +4256,7 @@ delete-window
 	  ;; Can't do without resizing fixed-size windows.
 	  (window--resize-siblings window (- size) horizontal t)))
 
-        (when (eq delete-window-choose-selected 'pos)
+        (when (eq choose-selected 'pos)
           ;; Remember edges and position of point of the selected window
           ;; of WINDOW'S frame.
           (setq frame-selected-window-edges
@@ -4289,7 +4290,7 @@ delete-window
                       ;; Select window at WINDOW's position at point.
 	              (set-frame-selected-window
                        frame new-frame-selected-window)))))
-         ((and (eq delete-window-choose-selected 'mru)
+         ((and (eq choose-selected 'mru)
                ;; Try to use the most recently used window.
                (let ((mru-window (get-mru-window frame nil nil t)))
                  (and mru-window
--