Re: [PATCH 02/10] bisect--helper: reimplement `bisect_next` and `bisect_auto_next` shell functions in C

["Miriam R." <mirucam@gmail.com>]

Hi Junio,

El jue., 27 feb. 2020 a las 17:41, Junio C Hamano
(<gitster@pobox.com>) escribió:
>
> "Miriam R." <mirucam@gmail.com> writes:
>
> >> It would be surprising if this code were correct.  It may be that it
> >> happens to (appear to) work because parents of the commit hasn't
> >> been painted and calling the helper only clears the mark from the
> >> commit (so we won't see repeated "painting down to the root commit")
> >> in which case this might be an extremely expensive looking variant
> >> of
> >>
> >>         commit->object.flags &= ~ALL_REV_FLAGS;
> >>
> >> that only confuses the readers.
> >>
> >> Even then, I think by clearing bits like SEEN from commit, it breaks
> >> the revision traversal machinery---for example, doesn't this mean
> >> that the commit we just processed can be re-visited by
> >> get_revision() without deduping in a history with forks and merges?
> >>
> >> Has this been shown to any of your mentors before sending it to the
> >> list?
> >
> > Adding clear_commit_marks() was a suggestion of a previous review of this patch:
> > https://public-inbox.org/git/nycvar.QRO.7.76.6.2001301619340.46@tvgsbejvaqbjf.bet/
> >
> > And of course, my mentor always reviews my patch series before sending.
>
> OK, I just didn't know how you and your mentors work.  Some leave
> their door open for mentees and help them when asked but otherwise
> act as an ordinary reviewer who somehow prioritises reviewing the
> work by their mentees.  So your mentors may be a better source of
> information why this piece of code, which I still do not know how it
> could be correct, is supposed to work.  Good.
>
> After reading the above URL, I think you may have misread the
> suggestion you were given.  Resetting using clear_commit_marks() may
> be necessary, but you do so when you finished walking so that you
> can do unrelated revision walk later.  For that, you clear the flag
> bits after the while() loop that asks get_revision() to yield
> commits are done, using the initial set of commits that you used to
> start iteration.
>
> That is how bisect.c::check_ancestors() work, that is
>
>  - it initializes a rev_info 'revs' from an array of commit rev[]
>
>  - it lets bisect_common() use the 'revs', which is allowed to
>    smudge the flag bits of commit objects.
>
>  - it uses clear_commit_marks_many() to clear the flags of the
>    commits whose flag bits may have been smudged and their
>    ancestors, recursively.  In order to use as the starting points,
>    the original array of commit rev[] that started the revision
>    traversal is used.

Thank you for your explanation.

To my understanding, it looks like calling reset_revision_walk() after
the while() loop should be enough. Am I right or am I missing
something?