bug#43469: 28.0.50; window-text-pixel-size returns incorrect value when line-prefix is set

[Yuan Fu]

> On Sep 18, 2020, at 3:22 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> From: Yuan Fu <casouri@gmail.com>
>> Date: Fri, 18 Sep 2020 13:05:15 -0400
>> Cc: 43469@debbugs.gnu.org
>> 
>>>> (progn (insert "xxxxxxxxxxxxxx")
>>>>      (print (car (window-text-pixel-size
>>>>                   nil (line-beginning-position) (line-end-position))))
>>>>      (put-text-property (line-beginning-position) (line-end-position)
>>>>                         'line-prefix "   ")
>>>>      (print (car (window-text-pixel-size
>>>>                   nil (line-beginning-position) (line-end-position)))))
>>>> 
>>>> Prints first 98, then 119
>>> 
>>> Why do you think this is a bug?
>> 
>> I thought the pixel width shouldn’t include the line-prefix?
> 
> It should.  From the function's doc string:
> 
>  This function exists to allow Lisp programs to adjust the dimensions
>  of WINDOW to the buffer text it needs to display.
> 
> When you want to know how wide a window you need for displaying some
> text, you do want the line-prefix part accounted for.

I see. I managed to use (window-text-pixel-size nil (point) (point)) to 
calculate the prefix width and subtract it out. Thanks.

Yuan