Re: [PATCH v4] user-manual: Add section "Why bisecting merge commits can be harder ..."

> Linus Torvalds <torvalds@linux-foundation.org> writes:
>
>> On Sat, 10 Nov 2007, Steffen Prohaska wrote:
>>> +
>>> +But if you already made a merge C instead of rebasing, all
>>> +is not lost.  In the illustrated case, you can easily rebase
>>> +one parent branch on top of the other after the fact, just
>>> +to understand the history and to make the history more
>>> +easily to bisect.
>>
>> I simply don't think this is true.
>>
>> You can *not* easily rebase after the fact. Both the parents may  
>> have lots
>> of merges independently of each other, and rebase won't be able to do
>> *anything* with such a case. In fact, the only reason you think  
>> you can
>> easily rebase after-the-fact is that you made the example history be
>> trivial. In real life, if the example history is that trivial (just a
>> single merge of two otherwise linear histories), you'd probably  
>> generally
>> not have this problem in the first place.
>>
>> The facts are:
>>
>>  - git bisect can handle merges quite well, and points to the right
>>    commit (which is *usually* not a merge).
>>
>>  - but merges by definition introduce changes from two independent  
>> lines
>>    of development, and while both lines may work well on their  
>> own, it is
>>    possible that (a) the merge itself was done incorrectly or (b)  
>> the two
>>    (or more) features that were introduced simply clash.
>>
>>  - "git rebase" won't do a thing for this after the fact, except in
>>    trivial cases, and even then it will generate a new history  
>> that simply
>>    isn't compatible with the original history, so while it could  
>> in theory
>>    help bisect things further in some limited and simple cases, in  
>> general
>>    it's simply not that useful an approach.
>>
>> ..and I think it's simply wrong to even *try* to imply that "git  
>> rebase"
>> can somehow change any of this.
>
> Very true.  It is a suggestion useful _only_ when you can easily
> rebase.  Like the one illustrated in the description, which is
> artificial and of very limited scope.  If you cannot rebase
> easily, then (by definition) rebase would not help you.