Re: [PATCH v10.1 7/7] bisect: allow any terms set by user

From: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Date: Jun 29, 2015, 09:32 UTC
Message-ID: <vpqsi9alv1l.fsf@anie.imag.fr>
In-Reply-To: <CAP8UFD1gWXOZHfiELZYgvGP1dA-aeaxbyaokKCut9pfWghy9uQ@mail.gmail.com>

Christian Couder <christian.couder@gmail.com> writes:

Show 9 quoted lines

> On Mon, Jun 29, 2015 at 9:34 AM, Matthieu Moy
>
>> As a user, when I
>> discovered "git bisect", I was actually surprised that it expected one
>> particular order between good and bad. I would have expected to be able
>> to say "this is good, this is bad, tell me where it changed" without
>> having an idea of who's good and who's bad.
>
> Maybe, but it's not how it has been developed.

... but it's how it would behave if we had this guessing feature. The user does not have to care whether we internally need "good is an ancestor of bad" if we can provide a user-interface which does not need that.

I find it particularly frustrating that we issue the message:

  "The merge base %s is bad.\n"
  "This means the bug has been fixed "
  "between %s and [%s].\n"

bisect is all about finding the commit where a property has changed, and here it stops, saying "I know it's between A and B, but I won't go further".

Show 11 quoted lines

>> In particular when bisecting from two branches, the user knows that
>> branch A is good, and branch B is bad, but does not necessarily know
>> whether it's a regression in B or a
>> fix in A. The fact that bisect can find out should be just "normal" from
>> the user point of view. There's no mistake involved, nothing to fix, and
>> nothing that went wrong.
>
> Well in this case, it's possible that the merge base is bad and what
> the user is interested in is the first bad commit that was commited
> before the merge base. We just don't know, in the case the merge base
> is bad, what is more interesting for the user.

The question asked by the user is "X is good, Y is bad, tell me where exactly it changed". We can't know for sure what is "interesting" for the user, but we can answer his question anyway.

Similarly, there can be several commits that introduce the same regression (this may happen if you cherry picked the guilty commit from branch A to branch B, and then merged A and B, or if you broke, fixed, and then broke again). bisect finds one transition from good to bad, but not all. It may or may not be the one the user wanted, but we can't know.

>> I think I prefer "term" to "name".
>
> Ok with that. I agree that it would be more consistent to have a "git
> bisect terms" and "--term-{old,new,bad,good}".

OK, I've applied it.

-- 
Matthieu Moy
http://www-verimag.imag.fr/~moy/