GNU bug report logs - #55847
29.0.50; line-number-at-pos ignores absolute parameter when checking position range

Previous Next

Full log

Message #13 received at control <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Antoine Kalmbach <ane <at> iki.fi>
Cc: 55847 <at> debbugs.gnu.org
Subject: Re: bug#55847: 29.0.50;
 line-number-at-pos ignores absolute parameter when checking position
 range
Date: Wed, 08 Jun 2022 17:02:32 +0300

tags 55847 notabug
thanks

> From: Antoine Kalmbach <ane <at> iki.fi>
> Date: Wed, 08 Jun 2022 14:44:10 +0300
> 
> 
> When working with a narrowed buffer, line-number-at-pos complains
> that the passed position parameter is out of range.
> 
> I believe this occurs because in fns.c there is check as follows:
> 
>    if (pos < BEGV || pos > ZV)

Yes, and that's by design.  With very rare exceptions, Emacs always
behaves as if text outside of the narrowed region doesn't exist.

This is not a bug.

> This works just fine when the buffer isn't narrowed, but narrowing
> affects BEGV. Suppose the buffer is narrowed, and you want to get the
> line number for position x where x is before where the current narrowing
> begins, passing (line-number-at-pos x t) now reports an error, because
> the correct thing to check is BEGV_BYTE, not BEGV.

You mean BEG, not BEGV_BYTE, I believe.  BEGV_BYTE is the _byte_
position corresponding to BEGV (which is a character position).

Anyway, if you want to get line-number-at-pos outside of the
restriction, you can simply do

  (save-restriction
    (widen)
    (line-number-at-pos POS))

This is what we do in Emacs if we want to access position outside of
the narrowed region.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.