bug#47300: delete-window to select window with same position

[Juri Linkov]

>> I don't know why, but sometimes `window-at' returns 'nil'.
>
> `window-at' is pretty useless anyway.  Try the below instead.
>
> (defun window-at-pos (x y &optional frame)

Thanks.  Now after tweaking I finally found what changes would make
the workable version:

diff --git a/lisp/window.el b/lisp/window.el
index fd1c617d6b..81a770ff32 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -4140,6 +4140,23 @@ window--in-subtree-p
                (throw 'done t)
              (setq parent (window-parent parent))))))))
 
+(defun window-at-pos (x y &optional frame)
+  "Return live window at position X, Y on specified FRAME.
+X and Y are counted in pixels from the origin at 0, 0 of FRAME's
+native frame.  FRAME must specify a live frame and defaults to
+the selected one.  Return nil if no such window can be found."
+  (setq frame (window-normalize-frame frame))
+  (catch 'window
+    (walk-window-tree
+     (lambda (window)
+       (let ((edges (window-edges window nil nil t)))
+        (when (and (>= x (nth 0 edges)) (< x (nth 2 edges))
+                   (>= y (nth 1 edges)) (< y (nth 3 edges)))
+          (throw 'window window))))
+     frame nil nil)))
+
+(defvar delete-window-use-posn-at-point t)
+
 (defun delete-window (&optional window)
   "Delete WINDOW.
 WINDOW must be a valid window and defaults to the selected one.
@@ -4162,7 +4179,7 @@ delete-window
   (let* ((frame (window-frame window))
         (function (window-parameter window 'delete-window))
         (parent (window-parent window))
-        atom-root)
+        atom-root posn-at-point-x posn-at-point-y window-at-posn-at-point)
     (window--check frame)
     (catch 'done
       ;; Handle window parameters.
@@ -4211,10 +4228,22 @@ delete-window
         (t
          ;; Can't do without resizing fixed-size windows.
          (window--resize-siblings window (- size) horizontal t)))
+        (when delete-window-use-posn-at-point
+          ;; Remember WINDOW's position at point.
+          (let ((edges (window-edges window nil nil t))
+                (posn-at-point (nth 2 (posn-at-point nil window))))
+            (when posn-at-point
+              (setq posn-at-point-x (+ (nth 0 edges) (car posn-at-point))
+                    posn-at-point-y (+ (nth 1 edges) (cdr posn-at-point))))))
        ;; Actually delete WINDOW.
        (delete-window-internal window)
        (window--pixel-to-total frame horizontal)
-       (when (and frame-selected
+        (when (and posn-at-point-x posn-at-point-y
+                  (setq window-at-posn-at-point
+                        (window-at-pos posn-at-point-x posn-at-point-y frame)))
+         ;; Select window at WINDOW's position at point.
+         (select-window window-at-posn-at-point))
+        (when (and frame-selected
                   (window-parameter
                    (frame-selected-window frame) 'no-other-window))
          ;; `delete-window-internal' has selected a window that should