Re: dired-do-find-regexp failure with latin-1 encoding

[Eli Zaretskii <eliz@gnu.org>]

> Cc: stephen.berman@gmx.net, emacs-devel@gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Sun, 29 Nov 2020 19:32:17 +0200
> 
> If the calls to the conversion program are done in parallel to the 
> subsequent searches, reading the file twice might not be a problem (with 
> the benefit of a disk cache).

How do you mean "in parallel"?  You cannot start searching until you
decide on the encoding, so it must not be in parallel.

> >> How does Emacs do it? Does it read until the end of the file?
> > 
> > No, just a small initial part of it.  That's one reason why the
> > results are not guaranteed to be correct.
> 
> But if we consider that approach good enough for Emacs, it should 
> probably be good enough for doing a search from inside Emacs.

It's good enough when the encoding is the locale's codeset, and in a
few other (not very important) cases.  For an arbitrary combination of
file's encoding and locale's codeset, the result can be wrong every
single time.

And searching in non-ASCII files whose encoding is not the locale's
native one is precisely the case where this will fail.  Granted, it's
a relatively rare use case, but when it does happen, all bets are off.

So reading just a small part, as Emacs does, will yield similar
percentage of wrong guesses.