Dear Sam,

thanks for getting contacting the asdf-devel mailing-list.

On Tue, Oct 15, 2013 at 2:19 PM, Sam Steingold <sds@gnu.org> wrote:
> I wonder why this function has a special case for clisp:
>
>   (defun rename-file-overwriting-target (source target)
>     #+clisp ;; But for a bug in CLISP 2.48, we should use :if-exists
> :overwrite and be atomic
>     (posix:copy-file source target :method :rename)
>     #-clisp
>     (rename-file source target
>                  #+clozure :if-exists #+clozure :rename-and-delete))
>
> it would seem that a more portable solution would be
>
> (defun rename-file-overwriting-target (source target)
>   #-clozure (when (probe-file target) (delete-file target))
>   (rename-file source target
>                  #+clozure :if-exists #+clozure :rename-and-delete))
>
One of the goals of that function is to be atomic if possible,
i.e. use the system call rename(2) on unix, or the equivalent on Windows
(MoveFileTransacted is the suggestion found by a quick Google search,
which is available starting with Windows Server 2008).

Most (all?) Unix implementations of CL already use that system call,
and it's just Clozure CL being pedantic about it.
That leaves Windows implementations. This code should probably be tested
and made to work on every implementation. I admit I don't have Windows,
and don't have the energy to fight to make it work there at this point, and I'm falling back to best effort. So, ahem, patches accepted.