bug#35899: 26.1; move-beginning-of-line sometimes does not move to beginning of line

[Eli Zaretskii <eliz@gnu.org>]

> From: Markus Triska <triska@metalevel.at>
> Date: Sat, 25 May 2019 15:31:57 +0200
> 
>     $ wget https://www.metalevel.at/ei/hello.png
> 
> and then, starting Emacs with "emacs -Q", evaluate the following form:
> 
>     (progn
>       (goto-char (point-min))
>       (save-excursion (insert "\n"))
>       (goto-char (+ (point) (cadr (insert-image-file "hello.png"))))
>       (move-beginning-of-line nil))
> 
> This yields: 592, and does not move point to the beginning of the line.
> 
> However, the documentation of move-beginning-of-line includes:
> 
>    (If there’s an image in the line, this disregards newlines
>    which are part of the text that the image rests on.)
> 
> Hence, I expect this to move to position 1. For comparison, when I press
> C-a, it does move to position 1, as expected.

"the text that the image rests on" refers to the text which is
"covered" by the display property, not the newlines in the binary data
that constitutes the image file's data.

> Would you please consider adjusting the function so that it behaves as
> documented?

This function works on the logical/physical lines, not on visual lines.

> Alternatively, could you please provide this feature in a different
> way?

I suggest to use beginning-of-visual-line instead.