Re: Git bisect does not find commit introducing the bug

["Jakub Narębski" <jnareb@gmail.com>]

W dniu 20.02.2017 o 08:38, Oleg Taranenko pisze:

>>>> Then you must adjust your definition of "good": All commits that do not have
>>>> the feature, yet, are "good": since they do not have the feature in the
>>>> first place, they cannot have the breakage that you found in the feature.
>>>>
>>>> That is exactly the situation in your original example! But you constructed
>>>> the condition of goodness in such a simplistic way (depending on the
>>>> presence of a string), that it was impossible to distinguish between "does
>>>> not have the feature at all" and "has the feature, but it is broken".
>>>
>>> Johannes, thank you for correctly identifying the error in my logic.
>>> Indeed I was using the term 'bad' also for the commit without the
>>> feature. In order to find the commit introducing the bug in my example
>>> a new state is needed, which would make 'git bisect' a bit more
>>> complicated than the user 'most of the time' probably needs. Or do you
>>> think, it would make sense to ask the user for this state (if e.g 'git
>>> bisect' would be started with a new parameter)?
> 
>> If a commit doesn't have the feature, then it is by definition, not
>> containing a broken feature, and you can simply use the "good" state.
>> There is no need for a different state. If you can't test the commit
>> because it's broken in some other way, you can use "git bisect skip"
>> but that isn't what you want in this case.
> 
> Commits missing feature == 'good' commit is a very confusing one.

Nowadays you can change the names for 'old' and 'new' with
`git bisect terms`.  HTH.
 
> Looks like in real life it happens much often, then git developers can
> imagine. For multi-branch/multi-feature workflow it's pretty easy not
> to recognize whether it is missing or not developed yet, especially on
> retrospective view where cherry-picking/squashing/merging is being
> used. My experience shows most annoying bugs are generating after a
> heavy merge (evil merge) with conflicts resolutions, where developer
> is not involved in the knowing what happens on counterpart changes.
> Then feature can be disappeared after it was worked & tested in its
> own branches.

Good to know about this problem.

> @Alex, I'm pretty interesting in fixing this weird bisect behaviour as
> well, as far as I struggled on it last summer and continue struggling
> so far :) If you want we can join to your efforts on fixing.

Anyway, I don't think it is feasible to weaken the assumption that there
is only one transition from 'old' ('good') to 'new' ('bad'); this is
what allows O(log(N)) operations.  See bisection method of root finding,
that is finding zeros of a continuous function.

Best,
-- 
Jakub Narębski