bug#77942: 31.0.50; replace-region-contents gets stuck

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: monnier@iro.umontreal.ca,  eggert@cs.ucla.edu,  77942@debbugs.gnu.org
> Date: Tue, 22 Apr 2025 13:42:15 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Cc: Paul Eggert <eggert@cs.ucla.edu>, 77942@debbugs.gnu.org
> >> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> >> Date: Tue, 22 Apr 2025 05:48:14 +0200
> >> 
> >> But honestly, what the heck? Does someone know what this diffing is
> >> about in the first place?
> >
> > It's about leaving the unchanged portions of text intact, including
> > their properties, overlays, markers, etc.  I believe the doc string
> > says that much.
> 
> What I meant is why perform an O(ND) diff for that purpose. That's not
> at all obvious.

AFAIU, it's because the Diff algorithm makes the minimum number of
changes.

> (And it would be nice if the doc string talked about
> that O(ND) a bit to warn users.)

It does:

  Because this function can be very slow if there is a large number of
  differences between the two buffers, there are two optional arguments
  mitigating this issue.