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Re: [mdt-ocl.dev] Playing with gerrit

Continuing with in-lined comments.

On 18/07/2013 12:26, Adolfo Sanchez-Barbudo Herrera wrote:
On 18/07/2013 10:42, Laurent Goubet wrote:
Adolfo,


To be honest I don't like this. Merging a potential long bunch of
commits, in which everyone has its purpose and comments, in just one,
makes me lose one of the essence of this agile quick changes oriented
methodology which I love.

I am not a fan of that requirement from gerrit myself, but one could
argue that it makes for a much more legible history, since you have your
features properly isolated in their commits.
You do not lose the history
of who did what, theirs comments and why they changed a particular
review : that history is logged on gerrit instead, through the comments
and various patch sets. For example, on
https://git.eclipse.org/r/#/c/13903/, you can see a "big"
feature-introducing commit. Gerrit keeps an history of the four distinct
patch sets that have been created for that particular feature along with
the comments we made during the reviews (on each patch set).

I prefer, features isolated by branching/merging. In one commit, you can't distinguish useful changes from those not so useful (regenarated code, releng changes). Moreover, if several people have been participating on a feature I don't know how authoring will be attributed in a squashed commit. I guess that in this situations, there will be different gerrit code review (dependent?). Anyway, in principle having to squash commits to request code review doesn't sound good to me.

Merging this with the next answer.


One would just need to look at the OCL repository's history to feel that
gerrit is an improvement :p. I really have trouble finding out what
commit introduced what change for which purpose in the (too) many
branches in there. Gerrit's "one commit for a change" tends to make for
a much clearer policy.

I'd have to think how our current workflow (branches policy for example) would change with gerrit. Actually, I'd like to see what happens when a change is successfully reviewed and submitted. My current gerrit experiment is currently based on master's commits. Many concerns:
- Are you, replacing a branch per feature/bug policy with this Gerrit usage ?
- What happens if the are several live pending code reviews?.
- Are they automatically merged when approved in case other approved reviews arrived before?
- What about of integrity/integration of the merged independent reviews (one could break the other)? What about if there are conflicts?

To me it looks like we still need a branches based development. In that case, rather than a clearer history one commit per feature/bug only ensures a shorter one ^^.

For big features, we still develop on branches, but we try never to push them on the eclipse repository. Not only are branches dangerous (you have to remember never to rebase a branch that has been pushed to a remote repository), but reviewing a long stream of commits seems useless : what we wish to review is the end result (tip of the dev branch), and how it changes from the existing state (master at the time of review, not at the branching time). Reviewing such branches is tedious and error-prone. Plus, IMHO, merging makes for a very messy and illegible history.

When we think that the new feature is ready, we prepare it for review by squashing the commits into a single one with a proper commit message, which we push for review. What you see in the review I've linked here (https://git.eclipse.org/r/#/c/13903/) is the result of such a squash.

The workflow described on https://wiki.openstack.org/wiki/Gerrit_Workflow is very similar to our use of git and gerrit, but there might be other, more sensible workflows (maybe something to ask on the EGit mailing list?).


I'll try this squeezed commit, perhaps it's the cause of the push
rejection. I guess that EGit doesn't have a way to this via UI, does it ?

That, I do not know. I rarely squash commits into one. Amending is
usually much easier when you work on a change :).

Some feelings I've got so far. It also requires be more careful when
committing/pushing, which could be error prone. Now we have push and
push to gerrit, I'm used to "commit and push" button (a normal push).
It sounds dangerous.

True enough, even very recently I've pushed to the repository a few
changes for which the review had not been completed. But that can be
avoided through a number of means :

  * disable the force push on your repository (you can no longer bypass
    gerrit)
      o On Compare, we've kept the force-push ability in order to avoid
        gerrit reviews when pushing the stream of very small changes I
        usually need when fixing build errors
Yes, having to pass through gerrit doesn't make sense. It would have to be a useless workflow of "I send a code review request", and "I approve my self".

Which you can actually do, however useless :p.


  * Make it so that your "normal" remote's push configuration is for
    gerrit. If your look at
    http://wiki.eclipse.org/EMF_Compare/Gerrit#Adding_a_new_remote, we
    add a "review" remote to our repositories so that we can push to
    gerrit via "git push review". This configuration can also be made to
    be your default instead of a new remote, so that "git push" pushes
    on gerrit directly.

Currently, my origin points to gerrit (Remote Push URL git.eclipse.org:29418/ocl/org.eclipse.ocl.git)

I don't know how this internally works, but my feelings are that we only have one remote repo. So a normal push will always udpate our unique GIT repo. The "push to gerrit" pushes to a different refs (refs/for rather than refs/heads) which in somehow are not exposed in the remote repo (nobody can fetch those refs, when fetching from the repository).

The URL is the same, what changes is the refspec in the "push" configuration. This is the same as what's behind the "push" and "push to gerrit" buttons of EGit (at least, I think it is the same) :
  • git push = git push origin HEAD:refs/heads/master => push to remote repository, bypassing gerrit
  • git push origin HEAD:regs/for/master => push to gerrit

The "new remote" we name "review" in the wiki page I linked above is no more than a shorthand for the second of these two (with "origin" being a shortcut itself for the URI of your repository). You could use something like this for example :

  • git config remote.origin.push HEAD:refs/for/master
    • This tells your "git push" and the EGit's "push" button to push a review instead of on the remote repository
  • git config remote.origin.push HEAD:refs/heads/master
    • Default configuration
Let's see if I finally complete a Gerrit contribution to see how the repository looks like. Meanwhile I'll login to build.eclipse.org to have a look via command line.

"login to build.eclipse.org to have a look via command line" ? This really scares me as to what you're going to do :p.

Cheers,

Laurent Goubet
Obeo

Cheers,
Adolfo.
--

Laurent Goubet
Obeo



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