Re: expand-file-name, DOS/Windows, and directory separator

[Eli Zaretskii]

> From: Eric Abrahamsen <eric@ericabrahamsen.net>
> Date: Tue, 15 Feb 2022 11:39:47 -0800
> 
> >> Can I rely on that behavior?
> >
> > I'd rather you didn't.  Why do you need such an assumption?  Emacs on
> > Windows can cope with file names that use any style of slashes.
> 
> This is code dealing with search results in Gnus, and the absolute file
> names need to be broken up so we can work on their segments. Right now
> that's done with regexps, which is ugly and fragile, and I'm just
> looking for the confidence that:
> 
> (file-name-split (expand-file-name <file> "/"))

file-name-split is one of the functions that support both styles of
slashes, so you don't need to call expand-file-name at all.  (And "/"
is not really an absolute file name on Windows anyway).

> Is going to return exactly the segments, no more no less, regardless of
> the system or separator type or whether there are multiple separators in
> a row, etc etc. No leftover slashes, no empty strings, all that.
> 
> (Okay empty strings are fine, I guess `file-name-split' always returns
> one for absolute file names.)

It would be a bug for file-name-split (or any other file-name-*
function, really) to fail to recognize the parts of a file name
depending on the style of slashes.  So if you find a case where the
results depend on the slashes, even without running the file name
through expand-file-name, please report that as a bug.