Re: Preserving branches after merging on ancestor

["Björn Steinbrink" <B.Steinbrink@gmx.de>]

On 2009.11.05 16:30:04 -0600, Jonathan Nieder wrote:
> But doing this misses some of the main benefits of feature branches
> imho.
> 
> If you base each feature branch on the stable release or features it
> depends on instead, this gives you the freedom to merge one feature without
> the others to another branch.

I guess Richard took the "branch topic1, merge topic1, branch topic2,
merge topic2" thing just as an example because that ends up with two
fast-forwards. And your example _still_ has such a fast-forward.

> For example:
> 
> # wouldn’t feature1 be neat? let me try it.
> git checkout -b feature1 v1.0
> hack hack hack
> # looks good.
> git commit -a
> 
> # how about an unrelated feature2?
> git checkout -b feature2 v1.0
> hack hack hack
> # looks good.
> git commit -a
> 
> # but do they work?
> git checkout v1.0; # detach head for testing [1]
> git merge feature1 feature2
> make check
> # hmm, these don’t seem to work well together
> ... (investigating some more)
> 
> # looks like feature1 is not ready for prime time
> # so let’s just use feature2 for now.
> git checkout master
> git merge feature2
> git branch -d feature2
> make check
> # looks good; better publish it.
> git push origin master
> 
> v1.0 --- feature1
>     \
>      \-- feature2 [master]

And here you got a fast-forward of master to feature2, i.e. linear
history, which is what Richard was trying to avoid.

Instead of:

A---B---C---D---E (topic2) (master)
     \
      F---G---H (topic1)

He wants:

      F---G---H (topic1)
     /
A---B-----------M (master)
     \         /
      C---D---E (topic2)

So he can see at which point topic2 got merged. This allows to ask "which
commits got merged here" (and for a merge-once topic branch this means:
Which commits are related to that topic), by using for example:

git log M^1..M^2 # Will show C, D and E

In the fast-forward case, there's no way to get that without manually
figuring out where the topic branch started.

Björn