Re: [RFC v2 1/1] refspec: add support for negative refspecs

[Jacob Keller <jacob.keller@gmail.com>]

On Thu, Sep 17, 2020 at 5:02 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Jacob Keller <jacob.e.keller@intel.com> writes:
>
> > @@ -66,6 +74,28 @@ static int parse_refspec(struct refspec_item *item, const char *refspec, int fet
> >       item->src = xstrndup(lhs, llen);
> >       flags = REFNAME_ALLOW_ONELEVEL | (is_glob ? REFNAME_REFSPEC_PATTERN : 0);
> >
> > +     if (item->negative) {
> > +             struct object_id unused;
> > +
> > +             /*
> > +              * Negative refspecs only have a LHS, which indicates a ref
> > +              * (or pattern of refs) to exclude from other matches. This
> > +              * can either be a simple ref, a glob pattern, or even an
> > +              * exact sha1 match.
> > +              */
> > +             if (!*item->src)
> > +                     return 0; /* negative refspecs must not be empty */
> > +             else if (llen == the_hash_algo->hexsz && !get_oid_hex(item->src, &unused))
> > +                     item->exact_sha1 = 1; /* ok */
> > +             else if (!check_refname_format(item->src, flags))
> > +                     ; /* valid looking ref is ok */
> > +             else
> > +                     return 0;
> > +
> > +             /* other rules for negative refspecs don't apply */
>
> This comment confused me a bit; did you mean "other rules don't
> apply to negative refspecs"?
>

Yea, this should be reworded.

> > +             return 1;
> > +     }
> > +
> >       if (fetch) {
> >               struct object_id unused;
>
>
> > diff --git a/remote.c b/remote.c
> > index c5ed74f91c63..2f583d72c3f0 100644
> > --- a/remote.c
> > +++ b/remote.c
> > @@ -1058,7 +1172,7 @@ static int match_explicit(struct ref *src, struct ref *dst,
> >       const char *dst_value = rs->dst;
> >       char *dst_guess;
> >
> > -     if (rs->pattern || rs->matching)
> > +     if (rs->pattern || rs->matching || rs->negative)
> >               return 0;
>
> OK.  These "special" ones do not participate in explicit matching.
>
> > @@ -1134,6 +1248,10 @@ static char *get_ref_match(const struct refspec *rs, const struct ref *ref,
> >       int matching_refs = -1;
> >       for (i = 0; i < rs->nr; i++) {
> >               const struct refspec_item *item = &rs->items[i];
> > +
> > +             if (item->negative)
> > +                     continue;
> > +
>
> And a negative one does not decide if a ref being pushed will be
> pushed out for real at this point.  This helper is only to enumerate
> the candidate refs to be pushed out; the caller makes a separate
> call to apply_negative_refspecs() to cull the candidate list later.
>
> OK.
>
> > @@ -1339,7 +1457,7 @@ int check_push_refs(struct ref *src, struct refspec *rs)
> >       for (i = 0; i < rs->nr; i++) {
> >               struct refspec_item *item = &rs->items[i];
> >
> > -             if (item->pattern || item->matching)
> > +             if (item->pattern || item->matching || item->negative)
> >                       continue;
> >
> >               ret |= match_explicit_lhs(src, item, NULL, NULL);
>
> match_explicit_lhs(), like match_explicit(), are for explicit
> matching and should not be called for the "special" ones.  OK.
>
> > @@ -1441,6 +1559,8 @@ int match_push_refs(struct ref *src, struct ref **dst,
> >               string_list_clear(&src_ref_index, 0);
> >       }
> >
> > +     *dst = apply_negative_refspecs(*dst, rs);
> > +
> >       if (errs)
> >               return -1;
> >       return 0;
>
> And after grabbing all the candidate refs to be updated via this
> push, we filter out the ones that match negative pattern.  Can it
> also produce an error, or it can never fail (to udpate errs)?
>
> > @@ -1810,6 +1930,9 @@ int get_fetch_map(const struct ref *remote_refs,
> >  {
> >       struct ref *ref_map, **rmp;
> >
> > +     if (refspec->negative)
> > +             return 0;
> > +
>
> Again, the idea is to let the existing codepath to only deal with
> the positive refspec elements to keep the same behaviour, and let
> the caller filter the ones that match negative ones out of the
> result.  So we return without anything here for negative one.
>

Yep, that's what I went for. The only real downside here is if we
forget a code path that should honor negative refspecs and doesn't,
because it will "accept" the refspec list with such a negative
refspec, but not do anything with it.

> Nothing jumped out at me as being suspicious so far, other than that
> the GNU "?<empty>:" thing needs to be fixed as pointed out by Dscho.
>
> Thanks.