Re: What is the best way to backport a feature?

On 2009.11.29 18:41:35 +0100, Peter Weseloh wrote:

quoted

 What's unusual there is that you merged from Mainline to Feature_A.
Usually, the history would look like this:

  o--o--o                    Release_1.0
 /    \  \
 o-o-o--o--o-o-o-o-o-o---o--o Mainline
     \                 /
      F1-----F2------F3      Feature_A

And then you could easily use rebase to get the job done.

But on the other hand the intermediate merges from the Mainline make for
much simpler merges, right?.
If merging is done only when Feature_A is ready it might become a real pain.

That's usually more often true with CVS or SVN than with git, but ...

It might take several month to complete it and the mainline might have
changed a lot.

... over such a long timeframe, yes, things might become ugly. OTOH such
a long timeframe might also mean that the topic branch actually does too
much. Splitting such a large thing into more manageable pieces would
help there, as you could merge completed topic branch to your mainline
branch earlier and more often.

quoted

Had you known beforehand that Feature_A is a candidate for backporting,
you would have even branch from an older commit like this:

  o--o--o                    Release_1.0
 /    \  \
 o-o-o--o--o-o-o-o-o-o---o--o Mainline
 \                     /
  F1--------F2-------F3      Feature_A

Then you could easily merge Feature_A to Release_1.0 as well, without
merging anything unrelated.

But that's just for the future...

Yes, sure. If I would know the future already today I would not need to do
any coding anymore :-)

I meant something like "I just said that, so you can avoid problems in
the future" ;-) But yeah, knowing beforehand that things should go into
a maintenance branch isn't common, unless it's about a bugfix.

quoted

Given you current history, you could use format-patch + am like this:

git format-patch --stdout --first-parent Mainline..Feature_A > fa.mbox
git checkout Release_1.0
git am -3 fa.mbox

The --first-parent options make it follow the first parent of the merge
commits only, so the whole stuff on the Mainline branch is ignored. And
you just get F1, F2 and F3 in fa.mbox, which you then apply using am.

Ah, great! I played with format-patch + am but missed the '--first-parent'
option. I will give it a try. Thanks a lot!

Well, it's a rev-list option, which might work by accident. Junio
recently said that the fact that format-patch accepts path limiting is
by accident, might be true for --first-parent as well... No clue. Junio?

Björn