Re: [PATCH] Create '--merges-only' option for 'git bisect'

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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Hi Tiago,

On Thu, 12 Apr 2018, Tiago Botelho wrote:

> On Thu, Apr 12, 2018 at 9:58 AM, Christian Couder
> <christian.couder@gmail.com> wrote:
> > On Thu, Apr 12, 2018 at 9:49 AM, Harald Nordgren
> > <haraldnordgren@gmail.com> wrote:
> >> I think it looks similar. But if I'm reading that thread correctly
> >> then there was never a patch created, right?
> >
> > (It is customary on this mailing list to reply after the sentences we
> > reply to. We don't "top post".)
> >
> > On the GSoC idea pages (like https://git.github.io/SoC-2018-Ideas/) we
> > have been suggesting "Implement git bisect --first-parent" and there
> > are the following related links:
> >
> > https://public-inbox.org/git/20150304053333.GA9584@peff.net/
> > https://public-inbox.org/git/4D3CDDF9.6080405@intel.com/
> >
> > Tiago in Cc also tried at a recent London hackathon to implement it
> > and came up with the following:
> >
> > https://github.com/tiagonbotelho/git/pull/1/files
> >
> > I tried to help him by reworking his commit in the following branch:
> >
> > https://github.com/chriscool/git/commits/myfirstparent
> 
> Thank you for the cc Christian, I’ve been quite busy and was not able
> to work on the PR for quite some time.
> 
> I intended to pick it back up again next week. If it is ok with Harald
> I would love to finish the PR that I started,
> since it is quite close to being finished (I think it was just specs
> missing if I am not mistaken).

That looks promising. Just like I suggested to Harald in another reply
[*1*] on this thread, you probably want to use `int flags` instead, and
turn `find_all` into BISECT_FIND_ALL in a preparatory commit.

Also, you will definitely want to add a test. Again, my reply to Harald
[*1*] should give you a head start there... You will want to imitate the
test case I outlined there, maybe something like:

# A - B - C - F
#   \   \   /   \
#     D - E - G - H

[... 'setup' as in my mail to Harald ...]

test_expect_success '--first-parent' '
	write_script find-e.sh <<-\EOF &&
	case "$(git show --format=%s -s)" in
	B|C|F) ;; # first parent lineage: okay
	*) git show -s --oneline HEAD >unexpected;;
	esac
	# detect whether we are "before" or "after" E
	test ! -f E.t
	EOF

	git bisect start --first-parent HEAD A &&
	git bisect run ./find-e.sh >actual &&
	test_path_is_missing unexpected &&
	grep "$(git rev-parse F) is the first bad commit" actual
'

Also, Tiago, reading through your patch (as on chriscool/git; do you have
your own fork? That would make it much easier to collaborate with you by
offering PRs), it looks more straight-forward than editing the commit_list
after the fact and adding magic weights ;-)

Except for one thing. I wonder why `bisect_next_all()` does not set
revs.first_parent_only after calling `bisect_rev_setup()`? You would still
need the changes in `count_distance()`, as it performs its own commit
graph traversal, but there is no need to enumerate too many commits in the
first place, right?

Harald, maybe --merges-only can be implemented on top of --first-parent,
with the `int flags` change I suggested?

Ciao,
Johannes

Footnote *1*:
https://public-inbox.org/git/nycvar.QRO.7.76.6.1804121143120.65@ZVAVAG-6OXH6DA.rhebcr.pbec.zvpebfbsg.pbz/