Subject: bug#23785: Emacs 25: "Undo" overdoes things.

From: [email-masked] (Phillip Lord)
Date: Fri, 17 Jun 2016 22:47:20 +0100

Eli Zaretskii <[email-masked]> writes:

>> I think there's a case to be made for fixing this bug for Emacs 25.1.
>
> It depends on what the fix will look like.  If it's simple and safe
> enough, I'll agree.

The following patch addresses the issue in my hands. I'd welcome
confirmation.

Stefan what do you think? You suggested something like this for
Bug#22295 also. I think that the problem is the same; if I read
insert-file-contents correctly, it disables collection of undo
information. I may well be reading it wrong though.

Given that this has turned up in two places now, it may be a wider
problem, and the more general solution might be the better one. It might
also invalidate the necessity for 12e009e52, but I haven't tested that
yet.

Alternatively, revert-buffer could just force undo-boundary.

Phil

>From 2ab1f314ad6fe0e68420cc510445495467d82b8f Mon Sep 17 00:00:00 2001
From: Phillip Lord <[email-masked]>
Date: Fri, 17 Jun 2016 22:34:50 +0100
Subject: [PATCH] Fix missing undo-boundary after revert-buffer

* lisp/simple.el (undo-auto--boundaries): Ensure an undo-boundary after
  every command whether it (apparently) changes the buffer or not.

Addresses Bug#23785
---
 lisp/simple.el | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lisp/simple.el b/lisp/simple.el
index b66827d..3110430 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -2875,6 +2875,10 @@ undo-auto--boundaries
   "Check recently changed buffers and add a boundary if necessary.
 REASON describes the reason that the boundary is being added; see
 `undo-last-boundary' for more information."
+  ;; (Bug #23785) All commands should ensure that there is an undo
+  ;; boundary whether they have changed the current buffer or not.
+  (when (eq cause 'command)
+    (add-to-list 'undo-auto--undoably-changed-buffers (current-buffer)))
   (dolist (b undo-auto--undoably-changed-buffers)
           (when (buffer-live-p b)
             (with-current-buffer b
-- 
2.8.4