If you can't merge a commit (based on 9.0.x) to master clearly, do you
need to file another PR anyway? Then the lag to get some code to master
increases a lot. I am not sure how useful is git tag --contains <sha1>
if you cannot be sure that you'll find all occurrences due to this kind
of issues.

R.

On 03/27/2017 11:33 AM, Sebastian Laskawiec wrote:
> Hey!
>
> We are about to start working on 9.1.x and 9.2.y branches so I would
> like to propose alternative merging strategy.
>
> Our current workflow looks like this:
>
> X - new commit
> X` - cherry pick to maintenance branch
> --+-------------------+-------X----- master
>   |                    \------X`---- 9.2.x
>   \---------------------------X``--- 9.1.x
>
> Each commit needs to be reviewed in master branch and backported to
> the maintenance branches. From maintenance perspective this is a bit
> painful, since in above example we need to get 3 times through PR
> queue. Also it's worth to mention that X is not X` nor X``.
> Cherry-picking creates a copy of a commit. This makes some useful
> tricks (like git tag --contains <sha1>) a bit harder to use. Finally,
> this approach allows the codebase to diverge from maintenance branches
> very fast (someone might just forget to backport some of the
> refactoring stuff).
>
> The proposal:
>
> X, Y - new commits
> / - merge commits
> --+---------+------/----/--- master
>   |          \----/---Y/---- 9.2.x
>   \-------------X/---------- 9.1.x
>
> With the proposal, a developer should always implement a given feature
> in the lowest possible maintenance branch. Then we will run a set of
> merges from 9.1.x into 9.2.x and finally into master. The biggest
> advantage of this approach is that given functionality (identified by
> a commit) will have the same SHA1 for all branches. This will allow
> all tools like (mentioned before) `git tag --contains <sha1>` to work.
> There are also some further implications of this approach:
>
>   * Merging commits should be performed very often (even automatically
>     in the night (if merged without any problems)).
>   * After releasing each maintenance release, someone will need to do
>     a merge with strategy `ours` (`git merge -s ours upstream/9.2.x`).
>     This way we will not have to solve version conflicts in poms.
>   * Since there is no nice way to rebase a merge commit, they should
>     be pushed directly into the master branch (without review, without
>     CI). After the merge, HEAD will change and CI will
>     automatically pick the build. Remember, merges should be done very
>     often. So I assume there won't be any problems most of the times.
>   * Finally, with this approach the code diverges slight slower (at
>     least from my experience). Mainly because we don't need to
>     remember to cherry-pick individual commits. They are automatically
>     "taken" by a merge.
>
> From my past experience, this strategy works pretty nice and can be
> almost fully automated. It significantly lowers the maintenance pain
> around cherry-picks. However there is nothing for free, and we would
> need to get used to pushing merged directly into master (which is fine
> to me but some of you might not like it).
>
> Thanks,
> Sebastian
>
>
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--
Radim Vansa <rvansa@redhat.com>
JBoss Performance Team

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