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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> buffer-modified-p is not the only parameter affected by juggling around
> the local variables. There will be undo history,
> buffer-chars-modified-tick, before/after-change-hooks triggered by
> `org-preserve-local-variables', etc.
>
> However, I do not see any obvious way how your proposed change can
> negatively affect all the above. Feel free to propose a patch.

I've written a patch proposal. It deals with buffer-modified-p and undo
history, but not the other two points you mention. I have tested it and
it works, but I had never dealt before with `buffer-undo-list' so maybe
there are some cases that I have not considered and for which this patch
could be problematic. Let me know what you think:


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From 14506bea13bf6278d95825257d90bbc3390ae8f1 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 | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/lisp/org-macs.el b/lisp/org-macs.el
index 19e5f42e9..64beeff53 100644
--- a/lisp/org-macs.el
+++ b/lisp/org-macs.el
@@ -163,16 +163,24 @@
 	  (org-with-wide-buffer
 	   (goto-char (point-max))
 	   (let ((case-fold-search t))
-	     (and (re-search-backward "^[ \t]*# +Local Variables:"
+	     (when (re-search-backward "^[ \t]*# +Local Variables:"
 				      (max (- (point) 3000) 1)
 				      t)
-		  (delete-and-extract-region (point) (point-max)))))))
+               (undo-boundary)
+	       (delete-and-extract-region (point) (point-max))))))
+         (tick-counter (buffer-modified-tick))
+         modified)
      (unwind-protect (progn ,@body)
        (when local-variables
+         (setq modified (< tick-counter (buffer-modified-tick)))
 	 (org-with-wide-buffer
 	  (goto-char (point-max))
 	  (unless (bolp) (insert "\n"))
-	  (insert local-variables))))))
+	  (insert local-variables))
+         (unless modified
+           (set-buffer-modified-p nil)
+           (setq buffer-undo-list
+                 (seq-drop-while 'identity buffer-undo-list)))))))
 
 (defmacro org-no-popups (&rest body)
   "Suppress popup windows and evaluate BODY."
-- 
2.25.1