Subject: Re: bug#71466: 30.0.50; Buffer-menu-group-by non-nil resets point when Buffer List is reverted

From: Juri Linkov <[email-masked]>
Date: Mon, 17 Jun 2024 09:35:11 +0300

> When point is on an entry, then 'tabulated-list-print'
> moves point to the entry with the same ID.
>
> However, what ID to prefer for outline heading lines
> is not quite clear.  Possible variants:
>
> 1. The simplest way would be to remember the position of point
>    or the line number.  But this is not quite reliable
>    when new entries are inserted before.
>
> 2. Remembering the outline heading line as a string and searching for it
>    afterwards would be ambiguous when there are more headings with the
>    same string.  For example, when at the top level there are project names,
>    and at the second level mode names repeated for every project.
>
> 3. To remember a complete path like outline-hidden-headings-paths does,
>    e.g. '("Project1 name" "Mode2 name").

The third variant is implemented now.

> But this will not handle modes that don't use tabulated-list.
> For example, reverting an xref buffer with outlines now restores
> visibility of outlines, but doesn't restore point.  OTOH, maybe it's
> not responsibility of outline-minor-mode to restore point when it's
> not on a heading line.

For xref I propose a separate patch that keeps point on the same line
after reverting the xref buffer:

diff --git a/lisp/progmodes/xref.el b/lisp/progmodes/xref.el
index fb6c9dad73b..1ff02d3712a 100644
--- a/lisp/progmodes/xref.el
+++ b/lisp/progmodes/xref.el
@@ -1017,7 +1017,9 @@ xref--xref-buffer-mode
               (lambda (&optional bound move backward looking-at)
                 (outline-search-text-property
                  'xref-group nil bound move backward looking-at)))
-  (setq-local outline-level (lambda () 1)))
+  (setq-local outline-level (lambda () 1))
+  (add-hook 'revert-buffer-restore-functions
+            #'xref-revert-buffer-restore-point nil t))
 
 (defvar xref--transient-buffer-mode-map
   (let ((map (make-sparse-keymap)))
@@ -1282,19 +1284,19 @@ xref-revert-buffer
     (when (boundp 'revert-buffer-restore-functions)
       (run-hook-wrapped 'revert-buffer-restore-functions
                         (lambda (f) (push (funcall f) restore-functions) nil)))
-    (save-excursion
-      (condition-case err
-          (let ((alist (xref--analyze (funcall xref--fetcher)))
-                (inhibit-modification-hooks t))
-            (erase-buffer)
-            (prog1 (xref--insert-xrefs alist)
-              (mapc #'funcall (delq nil restore-functions))))
-        (user-error
-         (erase-buffer)
-         (insert
-          (propertize
-           (error-message-string err)
-           'face 'error)))))))
+    (condition-case err
+        (let ((alist (xref--analyze (funcall xref--fetcher)))
+              (inhibit-modification-hooks t))
+          (erase-buffer)
+          (prog1 (xref--insert-xrefs alist)
+            (goto-char (point-min))
+            (mapc #'funcall (delq nil restore-functions))))
+      (user-error
+       (erase-buffer)
+       (insert
+        (propertize
+         (error-message-string err)
+         'face 'error))))))
 
 (defun xref--auto-jump-first (buf value)
   (when value
@@ -1309,6 +1311,13 @@ xref--auto-jump-first
    ((eq value 'move)
     (forward-line 1))))
 
+(defun xref-revert-buffer-restore-point ()
+  (let ((current-line (buffer-substring-no-properties (pos-bol) (pos-eol))))
+    (lambda ()
+      (goto-char (point-min))
+      (when (search-forward current-line)
+        (goto-char (pos-bol))))))
+
 (defun xref-show-definitions-buffer (fetcher alist)
   "Show the definitions list in a regular window.