Re: [BUG] org-copy-subtree in a file with local variables marks buffer as modified [9.5.3 (release_9.5.3-6-gef41f3 @ /home/ignacio/repos/emacs/lisp/org/)]

[Ignacio Casso <ignaciocasso@hotmail.com>]

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>> -		  (delete-and-extract-region (point) (point-max)))))))
>> +               (undo-boundary)
>
>> +           (setq buffer-undo-list
>> +                 (seq-drop-while 'identity buffer-undo-list)))))))
>
> This looks fragile and can be disasterous when buffer-undo-list is
> large.

I agree that it is very fragile, but could you explain why is it also
problematic with a large `buffer-undo-list'? I guess you mean
efficiency-wise, but it would only iterate through the few items added
since the call to (undo-boundary). Is there something else I'm not seeing?

> Maybe just use with-silent-modifications or some ideas from there (for
> example, wrapping modifications inside let-bound (buffer-undo-list t))?
> We should not inhibit modification hooks though. Otherwise, it will mess
> up with caching code.

Done. I attach the new patch:


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From 54e05dc54fe7091f2d1c7e0c44e01cf5abeb4907 Mon Sep 17 00:00:00 2001
From: Ignacio Casso <ignaciocasso@hotmail.com>
Date: Sun, 12 Jun 2022 10:38:53 +0200
Subject: [PATCH] Do not mark buffer as modified with
 org-preserve-local-variables

* lisp/org-macs.el (org-preserve-local-variables): Do not mark buffer
as modified or alter `buffer-undo-list' when body does not actually
modify the buffer.

This commit fixes a bug with `org-copy-subtree', which marked the
buffer as modified and added an entry to the undo list when the visited
file had local variables.
---
 lisp/org-macs.el | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lisp/org-macs.el b/lisp/org-macs.el
index 19e5f42e9..c34ff3ab7 100644
--- a/lisp/org-macs.el
+++ b/lisp/org-macs.el
@@ -166,13 +166,19 @@
 	     (and (re-search-backward "^[ \t]*# +Local Variables:"
 				      (max (- (point) 3000) 1)
 				      t)
-		  (delete-and-extract-region (point) (point-max)))))))
+               (let ((buffer-undo-list t))
+	         (delete-and-extract-region (point) (point-max)))))))
+         (tick-counter-before (buffer-modified-tick)))
      (unwind-protect (progn ,@body)
        (when local-variables
 	 (org-with-wide-buffer
 	  (goto-char (point-max))
 	  (unless (bolp) (insert "\n"))
-	  (insert local-variables))))))
+          (let ((modified (< tick-counter-before (buffer-modified-tick)))
+                (buffer-undo-list t))
+	    (insert local-variables)
+            (unless modified
+              (restore-buffer-modified-p nil))))))))
 
 (defmacro org-no-popups (&rest body)
   "Suppress popup windows and evaluate BODY."
-- 
2.25.1