bug#25181: 25.1.90; move-beginning-of-line doesn't move point

[Eli Zaretskii <eliz@gnu.org>]

> From: Andreas Röhler <andreas.roehler@easy-emacs.de>
> Date: Mon, 12 Dec 2016 12:49:05 +0100
> 
> Bug does not appear with Emacs -Q, as some fontification in buffer seems 
> to trigger it.
> 
> Text in buffer:
> 
> git reset HEAD test/2.sh
> 
> Cursor at pos 16. i.e. beginning of word "test".
> 
> C-a doesn't move point.

Please show a complete recipe, starting from "emacs -Q" (and loading
any optional packages/customizations as needed).  It's hard to discuss
an issue without being able to test-drive it.

> Watching move-beginning-of-line edebug, at line 6415
> 
>      (skip-chars-backward "^\n")
> 
> jumps correctly to BOL.
> 
> Error results from following later on:
> 
>      (setq first-vis-field-value
>        (constrain-to-field first-vis orig (/= arg 1) t nil))
> 
> Here first-vis-field-value is set to orig, i.e. pos 16, where it jumps 
> back-to, not leaving point at BOL.

I'm not sure I understood, but if I did, this is a feature: functions
such as beginning-of-line stop moving at field boundaries.

Once again, if you show an actual example, it will be much easier to
decide whether there's a bug here, and if so, what is it.

Thanks.