Re: [PATCH] Document 'git bisect fix'.

From: Michael J Gruber <git@drmicha.warpmail.net>
Date: Mar 16, 2011, 11:47 UTC
Message-ID: <4D80A33B.8020006@drmicha.warpmail.net>
In-Reply-To: <AANLkTimAaL-C_oH9X3QFUc+JOaSi7xVe93KYJuL0VEyR@mail.gmail.com>

Christian Couder venit, vidit, dixit 16.03.2011 10:52:

Show 25 quoted lines

> Hi,
> 
> On Mon, Mar 14, 2011 at 10:00 PM, Ralf Wildenhues
> <Ralf.Wildenhues@gmx.de> wrote:
>> git bisect is sometimes less effective than it could be in projects
>> with long-lived but simple bugs (e.g., little-tested configurations).
>> Rather than skipping vast revision ranges, it might be easier to fix
>> them up from known bugfix branches.
> 
> It's already possible to deal with this problem by creating a new
> branch where the bug is fixed, and then using "git replace", so that
> the new branch is used instead of the old one.
> Please search for "git replace" in this doc:
> 
> http://www.kernel.org/pub/software/scm/git/docs/git-bisect-lk2009.html
> 
>> 'git bisect fix' teaches bisect about when some known bug was
>> introduced and when it was fixed, so that bisect can merge in
>> the fix when needed into new test candidates.
> 
> Perhaps some people would find it easier to use what you suggest but
> using git replace may be nicer because you have to create the new
> branch once, so you need to fix merge or rebase problems only once.
> And the new branch may be useful not only for bisecting, for example
> to recreate old versions.

I'd say the replace method is perfect for transporting an existing fix "back in time" when the range of non-bisectable commits is limited. But since you have to replace the right (most recent) commit in that range it is less convenient when you have a fix due to a changed/exotic build environment or such which you do not want in your mainline.

Also, you have to rebase the whole history back to the commit which introduced the problem - and that could be the root commit if the bisect problems arise from a changed toolchain, like here.

Michael P.S.: Did you cull cc on purpose or did gmane mess up? Readding AM, LT, TG