bug#74208: 31.0.50; minibuffer read-file-name-default mutates global value of default-directory incorrectly

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 10 Nov 2024 16:47:17 +0530 (IST)
> Cc: monnier@iro.umontreal.ca, 74208@debbugs.gnu.org
> From: Madhu <enometh@meer.net>
> 
> *  Eli Zaretskii <eliz@gnu.org> <86ed3jl63j.fsf@gnu.org>
> Wrote on Sun, 10 Nov 2024 12:45:52 +0200
> >> I was evaluating it under edebug after calling edebug-defun on
> >> read-file-name-default, and ivoking (ffap) on the url.
> >>
> >> It returns the argument with or without the second parameter to
> >> expand-file-name, and I was hoping I could count on this behaviour to
> >> separate the urls from the files.
> >>
> >> The behaviour of expand-file-name is apparenlty modified when it comes
> >> to read-file-name-default, but I can't spot what's going on. ?????
> >
> > Perhaps because TRAMP was loaded?
> It's because of the call to
>  (ffap-read-file-or-url "foo" "https://example.com/")
> 
> which roughly does the equivalent of
> 
> (let ((file-name-handler-alist
>        (cl-adjoin (cons ffap-url-regexp #'ffap--url-file-handler)
> 		  file-name-handler-alist)))
>   (expand-file-name "https://example.com" "~"))
> 
> Maybe the idea will still work?

The idea being not to bind default-directory to the URL?  Doesn't ffap
need that?  If not, why does it override the file handlers?