bug#8035: Processing of .. in a file path after going thru symlink

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Thu, 26 Aug 2021 18:29:54 +0200
> Cc: 8035@debbugs.gnu.org
> 
> (file-exists-p "/tmp/comp/src/subdir/../foo.c")
> => nil
> (file-truename "/tmp/comp/src/subdir/../foo.c")
> => "/tmp/comp/dest/foo.c"
> (file-exists-p (file-truename "/tmp/comp/src/subdir/../foo.c"))
> => t
> 
> And this is because:
> 
> static Lisp_Object
> check_file_access (Lisp_Object file, Lisp_Object operation, int amode)
> {
>   file = Fexpand_file_name (file, Qnil);
> 
> I'm guessing it's calling expand-file-name here to resolve "~"?

No, because we always must call expand-file-name before invoking a
libc function that accesses files -- to support file names relative to
their buffer's default-directory.

> I think that `expand-file-name' call in check_file_access should be
> changed to something that just does the "~" expansion.

I don't think we can do that, for the reason explained above.