bug#22763: 25.1.50; Feature Request -- A faster method to obtain line number at position.

[Eli Zaretskii]

> Date: Thu, 20 May 2021 19:53:24 +0000
> From:  Ben Levy via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> I'm not 100% sure about this, but it looks like when
> line-number-at-pos was written in elisp, it didn't do
> any bounds check, and instead called (widen) before
> counting lines.  Did the elisp version have unintended
> behavior, or are the differences with the C version
> a regression?

I cannot answer that, because I don't understand what regression are
you talking about.

There's no need to widen the buffer in order to scan buffer text in C,
AFAIK.

> I think it's causing this bug:
> https://github.com/io12/good-scroll.el/issues/16

Please explain the connection.  I've read that discussion, but didn't
see any data that would indicate this function is the culprit.  At the
very least, please tell which arguments are passed to
line-number-at-pos in the problematic case, and what is the narrowed
region.