bug#38740: 28.0.50; cursor-sensor-mode error in post-command-hook

[Federico Tedin <federicotedin@gmail.com>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: Federico Tedin <federicotedin@gmail.com>
>> Date: Wed, 05 Feb 2020 21:24:35 +0100
>> Cc: 38740@debbugs.gnu.org
>> 
>> > Evaluating next form in scratch buffer:
>> >
>> >     (with-help-window "TEST"
>> >       (set-buffer standard-output)
>> >       (cursor-sensor-mode 1)
>> >       (insert "here"))
>> >
>> > Results in error:
>> >
>> >     Error in post-command-hook (cursor-sensor--detect): (args-out-of-range 354582)
>> >
>> > Looks like cursor-sensor uses scratch's window instead of "TEST" buffer window.
>> >
>> > I do not remember getting such error in Emacs 26, 27
>> 
>> I found that `cursor-sensor--detect' reads the point position from the
>> buffer displayed in the selected window, and then tries to read text
>> properties in that position in the current buffer. In your example,
>> those two buffers are not the same, the buffer at `standard-output'
>> isn't being displayed yet. I'm attaching a short patch that checks for
>> this case.
>
> LGTM, thanks.

I'm attaching the patch again but with the correct commit message
formatting.

- Fede


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From 5c9edf2f69ff531229f06c3dbedb468aef01e69a Mon Sep 17 00:00:00 2001
From: Federico Tedin <federicotedin@gmail.com>
Date: Mon, 17 Feb 2020 21:58:43 +0100
Subject: [PATCH] Fix cursor-sensor--detect when current buf != selected
 window's buf

* lisp/emacs-lisp/cursor-sensor.el (cursor-sensor--detect): Avoid
trying to read text properties from position taken from another
buffer.  (Bug#38740)
---
 lisp/emacs-lisp/cursor-sensor.el | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lisp/emacs-lisp/cursor-sensor.el b/lisp/emacs-lisp/cursor-sensor.el
index d8e8eeb16e..7728e78c47 100644
--- a/lisp/emacs-lisp/cursor-sensor.el
+++ b/lisp/emacs-lisp/cursor-sensor.el
@@ -146,9 +146,10 @@ cursor-sensor--detect
            ;; It's often desirable to make the cursor-sensor-functions property
            ;; non-sticky on both ends, but that means get-pos-property might
            ;; never see it.
-           (new (or (get-char-property point 'cursor-sensor-functions)
-                    (unless (<= (point-min) point)
-                      (get-char-property (1- point) 'cursor-sensor-functions))))
+           (new (and (eq (current-buffer) (window-buffer))
+                     (or (get-char-property point 'cursor-sensor-functions)
+                         (unless (<= (point-min) point)
+                           (get-char-property (1- point) 'cursor-sensor-functions)))))
            (old (window-parameter window 'cursor-sensor--last-state))
            (oldposmark (car old))
            (oldpos (or (if oldposmark (marker-position oldposmark))
-- 
2.21.1 (Apple Git-122.3)