Re: [PATCH 12/29] bisect--helper: reimplement `bisect_next` and `bisect_auto_next` shell functions in C

From: Christian Couder <christian.couder@gmail.com>
Date: Feb 17, 2020, 07:20 UTC
Message-ID: <CAP8UFD1UBPwYLUEdUJj3k1Yj0Y9dD6RyGh1dFL=wsSNihErqZQ@mail.gmail.com>
In-Reply-To: <nycvar.QRO.7.76.6.2001301619340.46@tvgsbejvaqbjf.bet>

Hi Dscho,

Thanks for your review! I agree with everything you said except a few things below.

On Thu, Jan 30, 2020 at 11:47 PM Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:

>
> On Mon, 20 Jan 2020, Miriam Rubio wrote:

Show 20 quoted lines

> > +static void prepare_rev_argv(struct bisect_terms *terms, struct argv_array *rev_argv)> > +{
> > +     struct string_list good_revs = STRING_LIST_INIT_DUP;
> > +     char *term_good = xstrfmt("%s-*", terms->term_good);
> > +
> > +     for_each_glob_ref_in(register_good_ref, term_good,
> > +                          "refs/bisect/", &good_revs);
> > +
> > +     argv_array_pushl(rev_argv, "skipped_commits", "refs/bisect/bad", "--not", NULL);
> > +     for (int i = 0; i < good_revs.nr; i++)
> > +             argv_array_push(rev_argv, good_revs.items[i].string);
> > +
> > +     string_list_clear(&good_revs, 0);
> > +     free(term_good);
> > +}
>
> Maybe we should fold that into `prepare_revs()`? We could then render the
> arguments directly into `revs` (via `add_pending_object()`, after setting
> obj->flags |= UNINTERESTING`) rather than formatting them into a string
> list, then deep-copy them into an `argv_array` only to parse them back
> into OIDs that we already had in the first place.

The current code is a straightforward port from shell. If we do what you suggest, yeah, it will be less wasteful, but on the other hand it will be less easy to see that we are doing a good job of properly porting code from shell. I suggest we try to focus on the later rather than the former right now, especially as performance is not very important here. Further improvements on top could be left for another patch series or perhaps as microprojects for GSoC or Outreachy applicants.

Using small functions also makes it easy to see that we are properly releasing memory. A previous version of this code had everything into a big function that used goto statements and it was less clear that we released everything.

Show 23 quoted lines

> > +static int bisect_skipped_commits(struct bisect_terms *terms)
> > +{
> > +     int res = 0;
> > +     FILE *fp = NULL;
> > +     struct rev_info revs;
> > +
> > +     fp = fopen(git_path_bisect_log(), "a");
> > +     if (!fp)
> > +             return error_errno(_("could not open '%s' for appending"),
> > +                               git_path_bisect_log());
> > +
> > +     res = prepare_revs(terms, &revs);
> > +
> > +     if (!res)
> > +             res = process_skipped_commits(fp, terms, &revs);
> > +
> > +     fclose(fp);
> > +     return res;
> > +}
>
> This is again a very short wrapper around another function, so it will
> probably make sense to merge the two, otherwise the boilerplate might very
> well outweigh the actual code doing actual work.

Yeah, there is perhaps a significant amount of boiler plate, but the code is much easier to check for leaks than when everything was in the same big function and there were goto statements, so I think it's a reasonable trade-off

Show 10 quoted lines

> > +             fclose(fp);
> > +     } else {
> > +             res = error_errno(_("could not open '%s' for "
> > +                                 "appending"),
> > +                               git_path_bisect_log());
> > +     }
>
> This pattern of opening a file, writing something into it, and then return
> success, otherwise failure, seems like a repeated pattern. In other words,
> it would be a good candidate for factoring out into its own function.

Yeah, but it seems that in this patch series we use the pattern only once. So I think it's fair to leave that for another patch series with cleanups and performance improvements or perhaps for microprojects.

Thanks, Christian.