4 files changed, 124 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 47275db47e3..2654d9d7995 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -309,9 +309,25 @@ It specifies how 'set-window-configuration' and 'window-state-put'
 should proceed with windows whose buffer was killed after the
 corresponding configuration or state was recorded.
 
+*** New variable 'window-point-context-set-function'.
+It can be used to set a context for window point in all windows by
+'window-point-context-set' before calling 'current-window-configuration'
+and 'window-state-get'.  Then later another new variable
+'window-point-context-use-function' can be used by
+'window-point-context-use' after 'set-window-configuration' and
+'window-state-put' to restore positions of window points
+according to the context stored in a window parameter.
+
 ** Tab Bars and Tab Lines
 
 ---
+*** New user option 'tab-bar-select-restore-context'.
+It uses 'window-point-context-set' to save contexts where
+window points were located before switching away from the tab,
+and 'window-point-context-use' to restore positions of window
+points after switching back to that tab.
+
+---
 *** New user option 'tab-bar-select-restore-windows'.
 It defines what to do with windows whose buffer was killed
 since the tab was last selected.  By default it displays
diff --git a/lisp/dired.el b/lisp/dired.el
index 9e3b888df14..f0113c002a4 100644
--- a/lisp/dired.el
+++ b/lisp/dired.el
@@ -2743,6 +2743,26 @@ Keybindings:
               '(dired-font-lock-keywords t nil nil beginning-of-line))
   (setq-local desktop-save-buffer 'dired-desktop-buffer-misc-data)
   (setq-local grep-read-files-function #'dired-grep-read-files)
+  (setq-local window-point-context-set-function
+              (lambda (w)
+                (with-current-buffer (window-buffer w)
+                  (let ((point (window-point w)))
+                    (save-excursion
+                      (goto-char point)
+                      (if-let ((f (dired-get-filename nil t)))
+                          `((dired-filename . ,f))
+                        `((position . ,(point)))))))))
+  (setq-local window-point-context-use-function
+              (lambda (w context)
+                (with-current-buffer (window-buffer w)
+                  (let ((point (window-point w)))
+                    (save-excursion
+                      (if-let ((f (alist-get 'dired-filename context)))
+                          (dired-goto-file f)
+                        (when-let ((p (alist-get 'position context)))
+                          (goto-char p)))
+                      (setq point (point)))
+                    (set-window-point w point)))))
   (setq dired-switches-alist nil)
   (hack-dir-local-variables-non-file-buffer) ; before sorting
   (dired-sort-other dired-actual-switches t)
diff --git a/lisp/tab-bar.el b/lisp/tab-bar.el
index fa22500a04e..05631c3c8f3 100644
--- a/lisp/tab-bar.el
+++ b/lisp/tab-bar.el
@@ -1292,6 +1292,9 @@ tab bar might wrap to the second line when it shouldn't.")
                                            frame 'buffer-list)))
          (bbl (seq-filter #'buffer-live-p (frame-parameter
                                            frame 'buried-buffer-list))))
+    (when tab-bar-select-restore-context
+      (window-point-context-set))
+
     `(tab
       (name . ,(if tab-explicit-name
                    (alist-get 'name tab)
@@ -1442,6 +1445,16 @@ if it was visiting a file."
           (setq buffer-read-only t)
           (set-window-buffer window new-buffer))))))
 
+(defcustom tab-bar-select-restore-context t
+  "If this is non-nil, try to restore window points from their contexts.
+This will try to find the same position in every window where point was
+before switching away from this tab.  After selecting this tab,
+point in every window will be moved to its previous position
+in the buffer even when the buffer was modified."
+  :type 'boolean
+  :group 'tab-bar
+  :version "30.1")
+
 (defvar tab-bar-minibuffer-restore-tab nil
   "Tab number for `tab-bar-minibuffer-restore-tab'.")
 
@@ -1539,6 +1552,9 @@ Negative TAB-NUMBER counts tabs from the end of the tab bar."
             (select-window (get-mru-window)))
           (window-state-put ws nil 'safe)))
 
+        (when tab-bar-select-restore-context
+          (window-point-context-use))
+
         ;; Select the minibuffer when it was active before switching tabs
         (when (and minibuffer-was-active (active-minibuffer-window))
           (select-window (active-minibuffer-window)))
diff --git a/lisp/window.el b/lisp/window.el
index 46de1819c69..3867f6fa6ef 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -10838,6 +10838,78 @@ displaying that processes's buffer."
                 (set-process-window-size process (cdr size) (car size))))))))))
 
 (add-hook 'window-configuration-change-hook 'window--adjust-process-windows)
+
+
+;;; Window point context
+
+(defun window-point-context-set ()
+  "Set context near the window point.
+Call function specified by `window-point-context-set-function' for every
+live window on the selected frame with that window as sole argument.
+The function called is supposed to return a context of the window's point
+that can be later used as argument for `window-point-context-use-function'.
+Remember the returned context in the window parameter `context'."
+  (walk-windows
+   (lambda (w)
+     (when-let ((fn (buffer-local-value 'window-point-context-set-function
+                                        (window-buffer w)))
+                ((functionp fn))
+                (context (funcall fn w)))
+       (set-window-parameter w 'context (cons (buffer-name) context))))
+   'nomini))
+
+(defun window-point-context-use ()
+  "Use context to relocate the window point.
+Call function specified by `window-point-context-use-function' to move the
+window point according to the previously saved context.  For every live
+window on the selected frame this function is called with two arguments:
+the window and the context data structure saved by
+`window-point-context-set-function' in the window parameter `context'.
+The function called is supposed to set the window point to the location
+found by the provided context."
+  (walk-windows
+   (lambda (w)
+     (when-let ((fn (buffer-local-value 'window-point-context-use-function
+                                        (window-buffer w)))
+                ((functionp fn))
+                (context (window-parameter w 'context))
+                ((equal (buffer-name) (car context))))
+       (funcall fn w (cdr context))
+       (set-window-parameter w 'context nil)))
+   'nomini))
+
+(add-to-list 'window-persistent-parameters '(context . writable))
+
+(defun window-point-context-set-default-function (w)
+  "Set context of file buffers to the front and rear strings."
+  (with-current-buffer (window-buffer w)
+    (when buffer-file-name
+      (let ((point (window-point w)))
+        `((front-context-string
+           . ,(buffer-substring-no-properties
+               point (min (+ point 16) (point-max))))
+          (rear-context-string
+           . ,(buffer-substring-no-properties
+               point (max (- point 16) (point-min)))))))))
+
+(defun window-point-context-use-default-function (w context)
+  "Restore context of file buffers by the front and rear strings."
+  (with-current-buffer (window-buffer w)
+    (let ((point (window-point w)))
+      (save-excursion
+        (goto-char point)
+        (when-let ((f (alist-get 'front-context-string context))
+                   ((search-forward f (point-max) t)))
+          (goto-char (match-beginning 0))
+          (when-let ((r (alist-get 'rear-context-string context))
+                     ((search-backward r (point-min) t)))
+            (goto-char (match-end 0))
+            (setq point (point)))))
+      (set-window-point w point))))
+
+(defvar window-point-context-set-function 'window-point-context-set-default-function)
+(defvar window-point-context-use-function 'window-point-context-use-default-function)
+
 
 ;; Some of these are in tutorial--default-keys, so update that if you
 ;; change these.