GNU bug report logs - #44581
28.0.50; undo comment-region error

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: bug-gnu-emacs <at> gnu.org
Subject: 28.0.50; undo comment-region error
Date: Wed, 11 Nov 2020 17:19:21 +0100

In *scratch*, write

abc def

Mark 'abc', run 'comment-region', then 'undo'.
This results in the error 

primitive-undo: Changes to be undone by function different from announced

with a backtrace if debug-on-error is set.

Message #8 received at 44581 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: 44581 <at> debbugs.gnu.org
Subject: bug#44581: 28.0.50; undo comment-region error
Date: Wed, 11 Nov 2020 17:33:22 +0100

This is a regression from Emacs 26; the bug is present on emacs-27 and master.

Message #11 received at 44581 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: 44581 <at> debbugs.gnu.org
Cc: Alan Mackenzie <acm <at> muc.de>
Subject: Re: bug#44581: 28.0.50; undo comment-region error
Date: Wed, 11 Nov 2020 19:43:28 +0100

This bug appears to be a consequence of eb0d10d567a. Alan, can you take a look?
The error does not appear if comment-combine-change-calls is set to nil.

Message #14 received at 44581 <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: 44581 <at> debbugs.gnu.org
Subject: Re: bug#44581: 28.0.50; undo comment-region error
Date: Sun, 15 Nov 2020 12:20:18 +0000

Hello, Mattias.

On Wed, Nov 11, 2020 at 19:43:28 +0100, Mattias Engdegård wrote:
> This bug appears to be a consequence of eb0d10d567a. Alan, can you take a look?
> The error does not appear if comment-combine-change-calls is set to nil.

Yes.  The region supplied to comment-region-default was (BEG END).  But
changes were made outside of this region (namely, deletion of
whitespace), so the invocation of macro combine-change-calls was
invalid.

Changing the END argument to combine-change-calls to
beginning-of-next-line solves this problem.

Maybe I need the same change in uncomment-region-default too, but I'm
not sure.

Here is a provisional patch, based on the master branch (although the
fix should probably go into emacs-27).  Could you test it, please.



diff --git a/lisp/newcomment.el b/lisp/newcomment.el
index e111ae8e22..3eb158dc2c 100644
--- a/lisp/newcomment.el
+++ b/lisp/newcomment.el
@@ -1292,7 +1292,15 @@ comment-region-default-1
 
 (defun comment-region-default (beg end &optional arg)
   (if comment-combine-change-calls
-      (combine-change-calls beg end (comment-region-default-1 beg end arg))
+      (combine-change-calls beg
+          ;; A new line might get inserted and whitespace deleted
+          ;; after END for line comments.  Ensure the next argument is
+          ;; after any and all changes.
+          (save-excursion
+            (goto-char end)
+            (forward-line)
+            (point))
+        (comment-region-default-1 beg end arg))
     (comment-region-default-1 beg end arg)))
 
 ;;;###autoload


-- 
Alan Mackenzie (Nuremberg, Germany).

Message #17 received at 44581 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: Alan Mackenzie <acm <at> muc.de>
Cc: 44581 <at> debbugs.gnu.org
Subject: Re: bug#44581: 28.0.50; undo comment-region error
Date: Sun, 15 Nov 2020 13:30:28 +0100

15 nov. 2020 kl. 13.20 skrev Alan Mackenzie <acm <at> muc.de>:

> Maybe I need the same change in uncomment-region-default too, but I'm
> not sure.

It seems more difficult to provoke uncomment-region to change text outside the region. Until we have a concrete example, better leave that code unchanged.

> Here is a provisional patch, based on the master branch (although the
> fix should probably go into emacs-27).  Could you test it, please.

Seems to work nicely. Thank you!

Message #22 received at 44581-done <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: 44581-done <at> debbugs.gnu.org
Subject: Re: bug#44581: 28.0.50; undo comment-region error
Date: Sun, 15 Nov 2020 13:31:59 +0000

Hello again, Mattias.

On Sun, Nov 15, 2020 at 13:30:28 +0100, Mattias Engdegård wrote:
> 15 nov. 2020 kl. 13.20 skrev Alan Mackenzie <acm <at> muc.de>:

> > Maybe I need the same change in uncomment-region-default too, but
> > I'm not sure.

> It seems more difficult to provoke uncomment-region to change text
> outside the region. Until we have a concrete example, better leave
> that code unchanged.

Yes, I agree.

> > Here is a provisional patch, based on the master branch (although the
> > fix should probably go into emacs-27).  Could you test it, please.

> Seems to work nicely. Thank you!

Thanks!  I've committed it to the emacs-27 branch, and I'm closing the
bug with this post.

-- 
Alan Mackenzie (Nuremberg, Germany).

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