Re: [git-for-windows] Re: Continuous Testing of Git on Windows

["Philip Oakley" <philipoakley@iee.org>]

From: "Johannes Schindelin" <Johannes.Schindelin@gmx.de>
> Hi Philip,
>
> On Tue, 14 Feb 2017, Philip Oakley wrote:
>
>> From: "Christian Couder" <christian.couder@gmail.com>
>> > On Tue, Feb 14, 2017 at 10:08 PM, Junio C Hamano <gitster@pobox.com>
>> > wrote:
>> > > Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
>> > >
>> > > > On Mon, 13 Feb 2017, Junio C Hamano wrote:
>> > > >
>> > > > > Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
>> > > > >
>> > > > > > That is why I taught the Git for Windows CI job that tests the
>> > > > > > four upstream Git integration branches to *also* bisect test
>> > > > > > breakages and then upload comments to the identified commit on
>> > > > > > GitHub
>> > > > >
>> > > > > Good.  I do not think it is useful to try 'pu' as an aggregate
>> > > > > and expect it to always build and work [*1*], but your "bisect
>> > > > > and pinpoint" approach makes it useful to identify individual
>> > > > > topic that brings in a breakage.
>> > > >
>> > > > Sadly the many different merge bases[*1*] between `next` and `pu`
>> > > > (which are the obvious good/bad points for bisecting
>> > > > automatically) bring my build agents to its knees. I may have to
>> > > > disable the bisecting feature as a consequence.
>> >
>> > Yeah, this is a bug in the bisect algorithm. Fixing it is in the GSoC
>> > 2017 Ideas.
>>
>> There are also a few ideas at the SO answers:
>> http://stackoverflow.com/a/5652323/717355
>
> Thanks for that link!
>
> However, my main aim was not to get distracted into yet another corner of
> Git that needs to be fixed (I am on enough of those projects already).
>
> I was merely surprised (and not in a good way) that a plenty ordinary
> bisect between `next` and `pu` all of a sudden tested a *one year old*
> commit whether it was good or not.
>
> And I doubt that the strategy to mark all second parents of all merge
> commits in pu..next as "good" would work well, as the merge bases *still*
> would have to be tested.

I was expecting that if all the second parents were marked as good, then 
there would be no merge bases, as there shouldn't be a forked graph, just 
the linear string of pearls - if bisect doesn't do that then there's an 
failed optimisation to be had.

I don't see anything in the `git bisect --help` page that would indicate 
that the merges themselves are omitted from the bisection.

>
> I guess what I have to resort to is this: if I know that `next` tests
> fine, and that `pu` fails, I shall mark all merge bases as "good". I am
> sure this has its own set of pitfalls, undoubtedly costing me more time on
> that front...
>
> But at least my cursory analysis of this idea seems to make sense: I use
> `next` essentially as a catch-all to verify that the breakage has entered
> `pu`, but not yet `next`. This reasoning makes sense, given that we know
> the waterfall topology of pu/next/master/maint: patches enter from left to
> right, i.e. anything that entered `pu` may later enter `next`, but not
> vice versa.

It may even be worth 'splitting' the pu branch sequence into the existing pu 
(with merges from series that are selected as reasonable), and then a pr 
branch (public review?) on top of that holding the rest of the series that 
have been submitted, so that the CI can do a full test on the tips of them 
to support those devs with limited test capability.


>
> Ciao,
> Dscho
>