Re: What's cooking in git.git (Apr 2017, #04; Wed, 19)

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Apr 22, 2017, 11:48 UTC
Message-ID: <alpine.DEB.2.20.1704221319580.3480@virtualbox>
In-Reply-To: <CAP8UFD19DVqQLHBta74uLcFPwJaRUKF8Ppmnhct5ub=OkKSqCQ@mail.gmail.com>

Hi Christian,

On Fri, 21 Apr 2017, Christian Couder wrote:

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> On Fri, Apr 21, 2017 at 11:50 AM, Johannes Schindelin
> <Johannes.Schindelin@gmx.de> wrote:
> >
> > (with all associated problems I reported earlier, as you apply some
> > patches on top of really ancient commits and bisect wants to test all
> > merge bases first)
> 
> First bisect should ask you to test merge bases only if there are
> "good" commits that are not ancestors of the "bad" commit.

Please note that this is a stateless job. The only "state" I have is the branch name.

So when something goes wrong, I have *no* indicator what is a known good state.

The strategy I implemented was to use knowledge about the branches and their relations. So when there is a bug in `pu`, the script first tests whether the same test passes in `next`. And if it does, that is my known-good state.

In the meantime, I cheat and mark all merge-bases as known-good, too. But that is by no means a correct assumption: sometimes Junio decides to base a patch on top of a really ancient commit, one that may be broken on Windows. So there you are, I cannot win, I just tried to implement something that works reasonably well, most of the time. It still takes way too long.

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> Second yeah there is probably an old bug in bisect there. In theory in
> most cases bisect should ask you to test only one merge base, as:
> 
> - if the merge base is "bad", it means that the bug has been fixed
> between the merge base and your "good" commit, and bisecting will
> stop,
> - if the merge base is "good", it means that all the merge bases that
> are ancestor of this merge base are also good, so there is no need to
> test them

That is not necessarily correct. If there are two merge bases, one may be broken, and then that one is the first bad commit.

Show 6 quoted lines

> > because the required time *definitely* would let Travis time out all
> > the time. Those bisect results are even less visible than the Travis
> > results, see e.g.
> > https://github.com/git/git/commit/2e3a8b9035a#commitcomment-21836854.
> 
> Nice that they exists though!

Yeah, well, it took enough of my time to implement, too ;-)

Ciao, Dscho