bug#46397: 27.1; Cannot delete buffer pointing to a file in a path that includes a file

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 46397@debbugs.gnu.org, craven@gmx.net
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Thu, 11 Feb 2021 18:20:44 -0800
> 
> On 2/11/21 2:14 PM, Matt Armstrong wrote:
> 
> > The issue isn't confined to exiting Emacs. It appears that once in a
> > "tricky situation where the file can't be unlocked for whatever reason"
> > Emacs will refuse to kill the buffer because unlock_file() signals an
> > error.
> 
> kill-buffer already asks the user something like "Buffer XXX modified; 
> kill anyway? (yes or no)" when killing a buffer that's been changed 
> without being saved. Perhaps it should also ask "File XXX cannot be 
> unlocked; kill buffer anyway? (yes or no)" if the file can't be unlocked.
> 
> > Note that shut_down_emacs() calls Fdo_auto_save() just before
> > unlock_all_files() and that call succeeds. Fdo_auto_save() also calls
> > report_file_errno, throwing an errno 13 (Permission denied), but that
> > recovers and continues.
> 
> Presumably shut_down_emacs should recover and continue if 
> unlock_all_files fails when it directly calls unlock_all_files.

That all is true, but I think we should provide for recovery in a way
that will work with _any_ command that calls unlock_file or
unlock_all_files.  Not just these two instances.  See my other message
about this.