[asdf-devel] Question about use of :unspecific

[Faré]

>> Should we use :unspecific based on a whitelist of known-working
>> implementations, or should we just avoid it altogether?
>
> Either of those seems OK to me.  I think a blacklist is probably wrong,
> just because it's too hard to update.
>
Agreed.

> OTOH, I don't really understand the motivation in two places here:
>
> 1.  I don't understand the rationale for the prohibition in the CLHS
> (probably someone from one of the implementation groups can say
> something about this) and
>
For backwards-compatibility probably, the CLHS allowed implementations
to NOT implement :unspecific. Some indeed don't (CLISP and ABCL at least).

> 2. I don't know the rationale for returning it from SPLIT-NAME-TYPE.  I
> understand that :unspecific has different behavior under merging (which
> is why I don't understand why it's forbidden), so it seems like one of
> two things should be the case:
>
>   a.  if you can return NIL for clisp and ABCL, it should be possible
> to return NIL for all the other implementations or
>
>   b.  if returning :unspecific is necessary for some implementations,
> shouldn't returning NIL on CLISP And ABCL fail?
>
I think that in practice, the parent pathname always has NIL in its type,
so that there is no difference between the merged pathname having type
NIL or :UNSPECIFIC.

> It seems like either these pathnames are never subjected to
> MERGE-PATHNAMES, in which case we can just always return NIL, or they
> /are/ sometimes subjected to MERGE-PATHNAMES, in which case sometimes
> the use of NIL instead of :unspecific will cause oddities (unless the
> default type is always empty).
>
Using :UNSPECIFIC seemed like it might produce more robust code.
But now that I realize the unportability, I don't care as much.

SBCL, CCL and LispWorks all pass janderson's tests just as well with
either NIL or :UNSPECIFIC. Haven't counted failures in other implementations.

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