bug#35939: version sort is incorrect with hyphen-minus

[Assaf Gordon]

Hello Paul,

On Wed, Jun 26, 2019 at 12:57:14PM -0700, Paul Eggert wrote:
> GNU sort uses the same algorithm as glibc strverscmp,

I think that both sort and ls use 'filevercmp' - a simplified version
that does not support locales (and doesn't fail).

The change (from 'strvercmp') was made in:

  commit e505736f8211a608b00dfe75fb186a5211e1a183
  Author: Kamil Dudka <address@hidden>
  Date:   Fri Oct 3 11:03:40 2008 +0200
  ls and sort: use filevercmp instead of strverscmp
  
https://git.savannah.gnu.org/cgit/coreutils.git/commit/?id=e505736f8211a608b00dfe75fb186a5211e1a183

> Has the Debian version-comparison algorithm changed since 1997? If so, could
> you give details about the changes to the Debian algorithm?

I don't think the algorithm changed in Debian,
and also in gnulib there are only a handful of relevant commits, all 10
years old:

  9121662f1 2008-10-03 filevercmp: new module
  0443c2f39 2009-03-05 filevercmp: Move hidden files up in ordering.
  1721cf06d 2009-03-24 filevercmp: handle simple~ and numbered.~3~ backup 
suffixes
  4fd008794 2009-04-09 filevercmp: fix regression
  cc96df30d 2009-04-09 filevercmp: correct today's change

I think (also based on Ian's confirmation) that this discrepancy was
from the beginning.

I now notice that there's an additional difference: coreutils/gnulib has
special handling for extension, hidden files and backup files.

As Ian wrote, a documentation improvement is probably the best fix.
I'll try to come up with a suggested change.

-assaf

P.S.

For completion, here are few other threads with details/explanations
about 'version-sort':
https://bugs.gnu.org/18168
https://bugs.gnu.org/22275
https://bugs.gnu.org/22455
https://bugs.gnu.org/33786