Re: Improve reporting of I/O, access errors for Emacs

[Eli Zaretskii <eliz@gnu.org>]

> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Thu, 12 Sep 2019 01:22:09 -0700
> 
> The basic idea is that Emacs should signal an error for serious and
> unexpected I/O errors (e.g., EIO, ENAMETOOLONG)

Why is that a good idea in general?  Emacs should do that when it
needs to operate on a file (like copy or rename or delete it), but
cannot due to some I/O error, that's a given.  But if Emacs just needs
to return some information about a file, and the file turns out to be
inaccessible, why do we need to signal an error instead of just
returning a failure indication?

IOW, I think your changes cause error signaling on too low a level,
where we cannot know whether signaling an error is or isn't a Good
Thing.  We should instead have such logic on higher levels, where the
semantics and the meaning of errors are clear.  Otherwise, we risk
breaking a lot of code which will suddenly need to deal with errors it
never saw before.