Re: Why can't I use git-bisect to find the first *good* commit?

[demerphq <demerphq@gmail.com>]

On 28 March 2011 20:23, Matthieu Moy <Matthieu.Moy@grenoble-inp.fr> wrote:
> Andrew Garber <andrew@andrewgarber.com> writes:
>
>> On Mon, Mar 28, 2011 at 1:55 PM, Matthieu Moy
>> <Matthieu.Moy@grenoble-inp.fr> wrote:
>>
>>> Then which commit do you specify as "good"?
>>
>> Any ancestral commit *on the same branch* which is know to be working.
>
> What is the point is finding manually a commit *on the same branch* when
> the tool can do that for you? You don't know how old the breakage is, so
> finding the first good commit will take some time. Knowing that the
> other branch is good gives you a hint that the common ancestor between
> branches should be good, so a good start would be to find the common
> ancestor.

This doesn't make a lot of sense to me. It is just as likely NOT to be useful.

It could just as easily have been fixed in the other branch. So
knowing its good wont tell you where it was broken.

This started off with:

      o--o--o--B
     /
  --o--o--o--o--G

So lets say that the reality of each node looks like this:

      B--B--B--B*
     /
  --B--B--B--G--G*

How does knowing that G* is good help us find what broke B* again?

Your description matches the case of something like this:

      B--B--B--B*
     /
  --G--G--G--G--G*

But what about something like this:

      Bx--B--B--B*
     /
  --Gz--By--B--Gx--G*

How does knowing that G* is good help you to find that Bx broke the
code in the B* branch again?

Presumably 'By' broke the G* branch which was then fixed by Gx and
none of this information helps you at all identify that Bx broke the
B* branch.

Whereas a plain binary search on the B* branch would eventually find
that Bx was responsible.

>> Perhaps you could give a concrete example of where you could use it
>> for multiple branches simultaneously?
>
> Well, see my previous email.

Where you said "It's not uncommon in real life to face the "it works
in branch foo but
not in branch bar, where did it break?" problem. And one expects a great
tool such as Git to be able to answer it."

Seems to me that this is trying to cram two questions into one:

A) where did branch foo diverge from branch bar and
B) which commit between that ancestor and bar did things break.

Of course im probably missing something important here. Id like to
know what it is tho. :-)

cheers,
Yves

-- 
perl -Mre=debug -e "/just|another|perl|hacker/"