Subject: bug#43375: 26.1: file-directory-p returns t for empty string

From: Boruch Baum <[email-masked]>
Date: Sun, 13 Sep 2020 12:29:00 -0400

On 2020-09-13 18:01, Eli Zaretskii wrote:
> > Date: Sun, 13 Sep 2020 10:39:43 -0400
> > From: Boruch Baum <[email-masked]>
> > Cc: [email-masked]
> >
> > > >   (file-directory-p "")
> > >
> > > This is not a bug, as Emacs always works with expanded and canonicalized
> > > file names (the result of applying expand-file-name).
> >
> > Then the docstring could be clearer and say "Return t if the expansion
> > of FILENAME names an existing directory"
>
> That's not a useful doc string, because "expansion of FILENAME" is not
> well defined, and is not easy to describe.
>
> I'm okay with making the doc string more clear, but let's please think
> about a more useful amendment.  A doc string should help the user
> understand what will/did happen, it shouldn't present puzzles.

How about:

  Return t if evaluating `expand-file-name' on FILENAME names an existing
  directory.

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