Re: [PATCH v2 09/11] bisect: libify `check_good_are_ancestors_of_bad` and its dependents

From: Miriam R. <mirucam@gmail.com>
Date: Jan 30, 2020, 14:40 UTC
Message-ID: <CAN7CjDCiP_KVC5Ey6cMuPN17vRNp_s4vy94qsaAKRPG=k3Rj3g@mail.gmail.com>
In-Reply-To: <nycvar.QRO.7.76.6.2001301341100.46@tvgsbejvaqbjf.bet>

Hi,

El jue., 30 ene. 2020 a las 14:46, Johannes Schindelin (<Johannes.Schindelin@gmx.de>) escribió:

Show 23 quoted lines

>
> Hi Miriam,
>
> On Tue, 28 Jan 2020, Miriam Rubio wrote:
>
> > @@ -893,18 +901,20 @@ static void check_good_are_ancestors_of_bad(struct repository *r,
> >       if (check_ancestors(r, rev_nr, rev, prefix))
> >               res = check_merge_bases(rev_nr, rev, no_checkout);
> >       free(rev);
> > -     if (res)
> > -             exit(res == -11 ? 0 : -res);
> >
> > -     /* Create file BISECT_ANCESTORS_OK. */
> > -     fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
> > -     if (fd < 0)
> > -             warning_errno(_("could not create file '%s'"),
> > -                           filename);
> > -     else
> > -             close(fd);
> > +     if (!res)
> > +     {
>
> Please move the opening `{` to the same line as the `if (!res)`.

Noted.

Show 21 quoted lines

>
> > +             /* Create file BISECT_ANCESTORS_OK. */
> > +             fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
> > +             if (fd < 0)
> > +                     warning_errno(_("could not create file '%s'"),
> > +                                   filename);
> > +             else
> > +                     close(fd);
> > +     }
>
> I wonder whether this would be easier to read:
>
>         if (res == -11)
>                 res = 0;
>         else if (res)
>                 ; /* error out */
>         else if ((fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600)) < 0)
>                 res = warning_errno(_("could not create file '%s'"), filename);
>         else
>                 close(fd);
>

Yes, I think it is a good improvement.

> Note: my code explicitly assigns `res = -1` if the file could not be
> created, which is technically a change in behavior, but I think it is
> actually a bug fix.

Aha.

If my mentor is ok with this change, I will apply the improvement you suggested :).

Show 27 quoted lines

>
> >   done:
> >       free(filename);
> > +     return res;
> >  }
> >
> >  /*
> > @@ -975,7 +985,9 @@ int bisect_next_all(struct repository *r, const char *prefix, int no_checkout)
> >       if (read_bisect_refs())
> >               die(_("reading bisect refs failed"));
>
> I see that there is still a `die()` here, and you left it alone in this
> patch because at this point, only the callers of
> `check_good_are_ancestors_of_bad()` need to be addressed. Good.
>
> At a later point, this will have to be dealt with, of course.
>
> Another thing will need to be handled, too: while I was looking at the
> code whether any resources need to be released (returning a negative
> integer does not release memory or close file handles, unlike `die()`), I
> stumbled across the fact that `term_bad` and `term_good` are file-local
> variables. They will need to be made attributes of a `struct` and will
> need to be released properly, i.e. the ownership will have to be clarified
> (is a failed `bisect_next_all()` responsible for releasing the memory it
> allocated via `read_bisect_terms()`, or its caller?).
>
> Just something to keep in mind. Or better: to jot down in a TODO list.

Ok. I will write this down for future improvements. Thank you!

Show 40 quoted lines

>
> >
> > -     check_good_are_ancestors_of_bad(r, prefix, no_checkout);
> > +     res = check_good_are_ancestors_of_bad(r, prefix, no_checkout);
> > +     if (res)
> > +             return res;
> >
> >       bisect_rev_setup(r, &revs, prefix, "%s", "^%s", 1);
> >       revs.limited = 1;
> > diff --git a/builtin/bisect--helper.c b/builtin/bisect--helper.c
> > index 826fcba2ed..3442bfe2cb 100644
> > --- a/builtin/bisect--helper.c
> > +++ b/builtin/bisect--helper.c
> > @@ -666,7 +666,8 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
> >
> >       switch (cmdmode) {
> >       case NEXT_ALL:
> > -             return bisect_next_all(the_repository, prefix, no_checkout);
> > +             res = bisect_next_all(the_repository, prefix, no_checkout);
> > +             break;
> >       case WRITE_TERMS:
> >               if (argc != 2)
> >                       return error(_("--write-terms requires two arguments"));
> > @@ -713,5 +714,12 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
> >               return error("BUG: unknown subcommand '%d'", cmdmode);
> >       }
> >       free_terms(&terms);
> > -     return !!res;
> > +     /*
> > +      * Handle early success
> > +      * From check_merge_bases > check_good_are_ancestors_of_bad > bisect_next_all
> > +      */
> > +     if (res == -11)
> > +             res = 0;
>
> Hmm. Is this the correct place, though? Should `bisect_next_all()` not be
> the function that already turns `-11` into `0`? In other words, _which_
> code are we supposed to skip over when `check_good_are_ancestors_of_bad()`
> returns `-11`? In other words, where would the `catch` of the
> `try`/`catch` be, if we had portable exceptions in C?

I think there must be a reason to do it there (but I don't know exactly), because there are some comments in code that say explicitly that this -11 to 0 is done in cmd_bisect_helper(), when the bisecting command exits.

Show 7 quoted lines

>
> > +
> > +     return res < 0 ? -res : res;
>
> This is a change in behavior, though: previously we guaranteed that the
> exit code is either 0 on success or 1 upon failure. I am not quite sure
> that we want to change that behavior.

I think this is because different error codes might enable a bisecting script calling the bisect command that uses this function to do different things depending on the exit status of the bisect command.

Thank you for reviewing. Best, Miriam.

Show 9 quoted lines

>
> Ciao,
> Dscho
>
> >  }
> > --
> > 2.21.1 (Apple Git-122.3)
> >
> >