bug#38641: 27.0.50; Misbehavior when drawing a rectangular selection with the mouse

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

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Thanks for the report. Would you try this patch?


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From f82164d1ca70fe7eb2208889cdf0ad2bdd1a06ec Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Mon, 16 Dec 2019 22:42:16 +0100
Subject: [PATCH] Adjust cursor column when auto-scrolling during rectangle
 selection

* lisp/mouse.el (mouse-drag-region-rectangle):
Move cursor to the correct column during auto-scrolling both when
crutches are used and not (bug#38641).
---
 lisp/mouse.el | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/lisp/mouse.el b/lisp/mouse.el
index 32996b2ede..e9156ffe35 100644
--- a/lisp/mouse.el
+++ b/lisp/mouse.el
@@ -2037,7 +2037,11 @@ mouse-drag-region-rectangle
                                (funcall adjusted-col mouse-col) 'point)
                             (unless mouse--rectangle-track-cursor
                               (forward-char))
-                            (rectangle--reset-point-crutches)))))
+                            (rectangle--reset-point-crutches))))
+               (scroll-adjust (lambda ()
+                                (move-to-column
+                                 (funcall adjusted-col mouse-col))
+                                (funcall set-col))))
           (if (and (eq window start-window)
                    mouse-row
                    (<= top mouse-row (1- bottom)))
@@ -2051,11 +2055,11 @@ mouse-drag-region-rectangle
              ((< mouse-row top)
               (mouse-scroll-subr
                start-window (- mouse-row top) nil start-point
-               set-col))
+               scroll-adjust))
              ((>= mouse-row bottom)
               (mouse-scroll-subr
                start-window (1+ (- mouse-row bottom)) nil start-point
-               set-col)))))))
+               scroll-adjust)))))))
     (condition-case err
         (progn
           (setq track-mouse t)
-- 
2.21.0 (Apple Git-122.2)