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

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: enometh@meer.net,  74208@debbugs.gnu.org
> Date: Sat, 23 Nov 2024 22:00:16 -0500
> 
> > Ping! How should we make progress with this issue?
> 
> I think the core of this bug report is that `shell-command` can fail
> when `default-directory` is set to a value that doesn't correspond to
> a local directory.
> 
> At least for things like `(shell-command "date")` this is undesirable.
> 
> Maybe `call-process` should try to "look for" a valid directory if
> `default-directory` isn't good enough?

It already does:

  Lisp_Object
  get_current_directory (bool encode)
  {
    Lisp_Object curdir = BVAR (current_buffer, directory);
    Lisp_Object dir = Funhandled_file_name_directory (curdir);

    /* If the file name handler says that dir is unreachable, use
       a sensible default. */
    if (NILP (dir))
      dir = build_string ("~");

I guess this case somehow evades the test?