Re: git merge and cherry-pick and duplicated commits?

[Johannes Sixt <j.sixt@viscovery.net>]

[Please reply-to-all on this list, to keep Cc: list]

skillzero@gmail.com schrieb:
> On Tue, Jan 13, 2009 at 11:34 PM, Johannes Sixt <j.sixt@viscovery.net> wrote:
> 
>> Well, the way to do it is "careful planning".
>>
>> If you have a *slight* suspicion that some change *might* be needed on a
>> different branch, then:
>>
>> 1. you commit the change on a branch of its own that forks off of the
>> merge-base of *all* the branches that *might* need it;
>>
>> 2. next, you merge this fix-up branch into the branch where you need it
>> first, which is very likely your current topic-under-development.
>>
>> 3. Later you can merge the branch into the other branches if you find that
>> it is really needed.
> 
> If I create a separate bug-fix-only branch X that forks from the
> latest common commit of all the branches that might need it and some
> of those branches already have commits after that merge base (e.g.
> branch Z is 5 commits after the common merge base by the time I fix
> the bug), will git be able to merge the new branch X into Z in a way
> that will allow me to also merge branch X into my original feature
> branch A and then later merge A into Z without duplicating the commit
> that is now in both branch X and Z?
> 
> It seems like I'd run into my original duplicate commit problem
> because even though branch X was originally based off the same parent
> commit, it will have a different parent when it is merged into Z
> because Z is no longer at that common merge commit (it's 5 commits
> beyond it).

After you created the fixup, you have this situation:

    o--o--o   <- A (feature branch)
   /
--o--x        <- X (the fix-up branch)
   \
    o--o--o   <- Z (probably your master)

You merge the fix-up into the feature branch and continue developing the
feature:

    o--o--o--M--o--o   <- A
   /        /
--o--x-----'           <- X
   \
    o--o--o            <- Z

Other people need the fix in Z right now, so you merge it into Z as well:

    o--o--o--M--o--o   <- A
   /        /
--o--x-----<           <- X
   \        \
    o--o--o--N         <- Z

You complete your feature and merge it into Z:

    o--o--o--M--o--o     <- A
   /        /       \
--o--x-----<         \   <- X
   \        \         \
    o--o--o--N---------O <- Z

The fix-up commit is only once in your history.

-- Hannes