bug#21730: 25.0.50; Random errors in redisplay--pre-redisplay-functions

[Eli Zaretskii]

> From: Philipp Stephani <p.stephani2@gmail.com>
> Date: Wed, 14 Sep 2016 18:43:13 +0000
> Cc: 21730@debbugs.gnu.org, mwd@md5i.com
> 
>  Since the problem that caused the patch to be reverted was with
>  narrowing, why not simply use
> 
>  (= point (with-current-buffer (window-buffer window) (point-min)))
> 
>  instead of
> 
>  (= point 1)
> 
>  ?
> 
> This has the same issues as described above. There's more code in 
> cursor-sensor--detect that assumes (eq
> (current-buffer) (window-buffer window)), e.g. the form (get-char-property 
> point 'cursor-sensor-functions).
> Therefore (= point (with-current-buffer (window-buffer window) (point-min))) 
> must be the same as (bobp).
> Another mystery is the stack trace entry 
> "run-hook-with-args(cursor-sensor--detect #<window 224 on
> *Group*>)". How can cursor-sensor--detect be the first argument to 
> run-hook-with-args? Shouldn't it always
> be pre-redisplay-functions?

If we want to dig deeper, I think we should first understand why bop
doesn't work.  Is it indeed because the window's buffer is not the
current buffer when the hook is called?