Re: [RFC PATCH 3/5] pack-objects: add delta-islands support

[Christian Couder <christian.couder@gmail.com>]

On Tue, Jul 24, 2018 at 7:11 PM, Junio C Hamano <gitster@pobox.com> wrote:
>
> Another thing I noticed from 2/5 is that you can have up to 7 such
> capture groups.  I do not have any opinion if 7 is too few or too
> many, but we would want the number to be documented, and end-user
> input diagnosed when it requires more captures than we support (if
> we are not already checking, that is).

This is the new documentation:

-> Refs are grouped into islands based on their "names", and two regexes
-> that produce the same name are considered to be in the same
-> island. The names are computed from the regexes by concatenating any
-> capture groups from the regex, with a '-' dash in between. (And if
-> there are no capture groups, then the name is the empty string, as in
-> the above example.) This allows you to create arbitrary numbers of
-> islands. Only up to 7 such capture groups are supported though.

I added the last sentence above, but I wonder if it is 7 or 8. The
code is the following:

-> static int find_island_for_ref(const char *refname, const struct
object_id *oid,
->                    int flags, void *data)
-> {
->     int i, m;
->     regmatch_t matches[8];
->     struct strbuf island_name = STRBUF_INIT;
->
->     /* walk backwards to get last-one-wins ordering */
->     for (i = island_regexes_nr - 1; i >= 0; i--) {
->         if (!regexec(&island_regexes[i], refname,
->                  ARRAY_SIZE(matches), matches, 0))
->             break;
->     }

I also wonder if the above is enough to diagnose end-user input when
it requires more captures than we support. A quick look at the man
page of the regex functions wasn't enough to enlighten me. Any input
on these issues is very welcome!