Re: cherry picking and merge

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From: "Mike Stump" <mikestump@xxxxxxxxxxx>
Sent: Friday, August 01, 2014 11:10 PM
(part 2)
On Aug 1, 2014, at 11:57 AM, Philip Oakley <philipoakley@xxxxxxx> wrote:
For some central control use styles, the ideas behind _distributed_ version control are anathema and (Git) just grinds away at the policies that are expected.
...
of the 'relativity' that comes with being distributed - truth has to give way to a web of trust). Also the artefacts that Git validates are at a different level of abstraction i.e. the whole project as a commit, rather than just a few/one file at a time.

Ah, so that gives me an idea. [ pause ] If we try the cherry-pick as retroactively creating a feature branch, cherrying into that, then merge unconditionally so that no change happens that into trunk (thus killing those conflicts), and then git merge that feature branch into branch then it all works perfectly. See, another existence proof that you are wrong, this time with git itself.

It was 13 lines of code, so, apparently, it is possible and easy to do, in git. Now, we just want the cherry-pick to create a temporary cherry branch, cherry the pick into it, merge and drop into trunk and merge into branch…

I tested with the below and it worked just fine. Things to clean up, we want the meta data on the cherry on the merge commit, but, you get the idea.


I've annotated some of the bits to make sure we are on the same wavelength as to what this does...

branch=b
master=master
base=$(git merge-base $branch $master)

cherry="$1" # not quite sure where this commit is located relative to either $branch or $master


# create a new branch, starting at base, for our cherry picked commit
git checkout -b cherry-$branch $base
git cherry-pick "$cherry" # which also commits onto our cherry pick barnch

git checkout $master
git merge -s ours cherry-$branch # "mark/remember" the cherry branch, its fix and it's base point, but don't actualy use it here on $master

git checkout $branch
git merge cherry-$branch # bring the 'fix' into $branch

git branch -d cherry-$branch # remove the fix branch that started at $base - branches are ephemeral anyway.

# still on $branch, which already has the change merged in (Git style) ?
git cherry-pick --strategy=ours --allow-empty "$cherry" # check its all already included?
git commit --allow-empty


Does my annotation match your understanding? It wasn't clear to me where $1 had been hiding previously, nor why the common fix didn't use a "merge -s ours cherry-$branch" in both cases - that maybe my misunderstanding about how your workflow goes.

I tested that with two cherries with further changes on master to ensure that it works for more than a single one, no problem. Wow, even tried a merge of master back into b, and it worked just fine, no conflicts, yet, all the code was jammed up together nicely.

So, if you wish to continue your position, please explain why it can’t get this better, given the existence proof above of it working better in git.

...
I have two possible conflict fixups in the above. In my case (I have a specific patch in gcc-land i wanted to cherry), those fixups were trivial (no conflicts). When they are trivial, I don’t care much that there were two of them. When non-trivial, well, I’m resigned to the idea that I have to explain what is going on.

Selecting a compatible workflow is a problem of usage,

Not when the workflow is mandated on you to work around trivial little bugs that can be fixed but for which the author’s don't even comprehend the bug.

rather than a problem in Git.
--


Philip.
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