bug#18310: 24.3.93; relative links don't work in eww and Windows 7

[Eli Zaretskii <eliz@gnu.org>]

> From: joaotavora@gmail.com (João Távora)
> Cc: 18310@debbugs.gnu.org
> Date: Thu, 21 Aug 2014 16:43:48 +0100
> 
> Something other than `default-directory' seems to be influencing it. I
> did some tests:

Like I said: Emacs uses the current drive to complete the missing
drive letter.  That is what you see.

> Finally
> 
>    (let ((default-directory "\\\\"))
>      (expand-file-name "../" "/something/bla"))
> 
> Crashed the Emacs process on my machine.

It's not a crash, it's a deliberate abort.  "\\\\" (i.e., 2
backslashes in a row without anything after that) is an invalid file
name on Windows.  Just don't do that.

> The docstring should explain its relationship with the
> `default-directory' variable, which in the current version sounds like
> it's shadowed completely by the DEFAULT-DIRECTORY parameter. Perhaps a
> sentence could be added.
> 
>    If DEFAULT-DIRECTORY is nil or missing, the current buffer's value of
>    `default-directory' is used. Even if DEFAULT-DIRECTORY is non-nil,
>    `default-directory' may still be used to help canonicalize the
>    resulting name for the current platform.

How does that obscure hint help?  It doesn't tell anything that mere
mortals could understand.

Once again, you are talking about semi-invalid use cases.  IMO,
complicating the doc string (which is not at all simple as it is) on
behalf of those use cases is not TRT.

> PS: Had a look at `url-expand-file-name': isn't it doing to much for
> `shr-expand-url''s purposes?

I have no idea, but as long as you need to resolve relative URLs, it
is your friend.