From: Junio C Hamano <gitster@pobox.com>
Date: Mon, 30 Jun 2008 22:44:55 GMT
Subject: Re: [PATCH] bisect: error out when given any good rev that is not an ancestor of the bad rev
Message-ID: <7v3amuv8yg.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <20080701004211.ba9b89c9.chriscool@tuxfamily.org>

Christian Couder <chriscool@tuxfamily.org> writes:

> Before this patch "git bisect" doesn't really work when it is given
> some good revs that are siblings of the bad rev.
>
> For example if there is the following history:
>
> A-B-C-D
>    \E-F
>
> and we launch "git bisect start D F" then only C and D will be
> considered as possible first bad commit. This is wrong because A, B and
> E may be bad too if the bug exists everywhere except in F that fixes it.

Please don't.

bisect is about finding a single regression by partitioning the graph into
older good section and newer bad section with a *single* "first bad
commit".

For your "this could also be possible" scenario is already outside the
realm.  You are assuming A, B and F is good, and D is bad.  But if E is
bad, then that breakage cannot possibly affect the transition between B
and D from good to bad (E cannot break D), so C must *also* be bad.