bug#37700: 27.0.50; undo mouse-drag-and-drop-region ineffective

["Mattias Engdegård" <mattiase@acm.org>]

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30 okt. 2019 kl. 20.56 skrev Stefan Monnier <monnier@iro.umontreal.ca>:
> 
>> Unfortunately, even with the patch, undoing a drag-and-drop does not leave
>> the region active the way it was before the undo, so the user has to
>> reselect the text in order to try again.
> 
> If the undo-list is built right, reselecting the text should be just
> `C-x C-x`, which isn't that bad.

Right, second nature to the Emacs user, but it would still be nice not having to go through that step. kill-region and delete-selection-mode are similarly affected.

> But now that I think about it, maybe a better option would be to check
> 
>    (when (symbolp last-command)
>      (get last-command 'undo-inhibit-region))
> 
> and then put the `undo-inhibit-region` property on
> `mouse-drag-and-drop-region`.

Thank you, this looks like the best idea so far. A very simple change, yet effective in practice. Not perfect --- last-command is not buffer-local, and even switching to a different frame and back will change it --- but good enough.

Patch attached.


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From 7cf5f680ab1d933fe1cecb862afa3b0976045f1d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Thu, 31 Oct 2019 10:31:27 +0100
Subject: [PATCH] Inhibit undo-in-region for mouse-drag-region (bug#37700)

'mouse-drag-region' leaves the region active around the dragged text,
so a straight undo did not revert the entire operation.  To remedy
this, inhibit undo-in-region when the last command was
mouse-drag-region.  (Method suggested by Stefan Monnier.)

* lisp/mouse.el (undo-drag-region): Set the undo-inhibit-region property.
* lisp/simple.el (undo): Inhibit undo-in-region if the last command
had the undo-inhibit-region property set.
---
 lisp/mouse.el  | 6 ++++++
 lisp/simple.el | 7 ++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/lisp/mouse.el b/lisp/mouse.el
index 76fec507e7..4a351f7be2 100644
--- a/lisp/mouse.el
+++ b/lisp/mouse.el
@@ -1104,6 +1104,12 @@ mouse-drag-region
     (run-hooks 'mouse-leave-buffer-hook)
     (mouse-drag-track start-event)))
 
+;; Inhibit the region-confinement when undoing mouse-drag-region
+;; immediately after the command.  Otherwise, the selection left
+;; active around the dragged text would prevent an undo of the whole
+;; operation.
+(put 'mouse-drag-region 'undo-inhibit-region t)
+
 (defun mouse-posn-property (pos property)
   "Look for a property at click position.
 POS may be either a buffer position or a click position like
diff --git a/lisp/simple.el b/lisp/simple.el
index 29e195bca6..10aecd651f 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -2508,6 +2508,10 @@ undo
 	 (base-buffer (or (buffer-base-buffer) (current-buffer)))
 	 (recent-save (with-current-buffer base-buffer
 			(recent-auto-save-p)))
+         ;; Allow certain commands to inhibit an immediately following
+         ;; undo-in-region.
+         (inhibit-region (and (symbolp last-command)
+                              (get last-command 'undo-inhibit-region)))
 	 message)
     ;; If we get an error in undo-start,
     ;; the next command should not be a "consecutive undo".
@@ -2525,7 +2529,8 @@ undo
 		       ;; it shows nothing else happened in between.
 		       (gethash list undo-equiv-table))))
       (setq undo-in-region
-	    (or (region-active-p) (and arg (not (numberp arg)))))
+	    (and (or (region-active-p) (and arg (not (numberp arg))))
+                 (not inhibit-region)))
       (if undo-in-region
 	  (undo-start (region-beginning) (region-end))
 	(undo-start))
-- 
2.21.0 (Apple Git-122)