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From Marco de Abreu <marco.g.ab...@googlemail.com>
Subject Re: Switch PR validation to PR-merge
Date Wed, 10 Jan 2018 20:40:53 GMT
Thanks for your opinions. Could a committer please contact a mentor in
order to create an Apache Infra ticket to change the protected master
branch from PR-head to PR-merge?

-Marco

On Wed, Jan 10, 2018 at 9:26 PM, kellen sunderland <
kellen.sunderland@gmail.com> wrote:

> +1
>
> On Wed, Jan 10, 2018 at 6:51 PM, Gautam <gautamnitc@gmail.com> wrote:
>
> > +1
> >
> > On Jan 10, 2018 1:25 AM, "Marco de Abreu" <marco.g.abreu@googlemail.com>
> > wrote:
> >
> > > Hello,
> > >
> > > TLDR: We wish to change how PRs are validated, turning off PR-head
> which
> > > tests PRs in their current branch, and turning on PR-merge, which tests
> > PRs
> > > rebased on the current master branch.  We believe this will catch more
> > > potential errors that would otherwise get merged into master, and it
> > should
> > > not cause any extra work for commiters or reviewers.
> > >
> > > as announced in
> > > https://lists.apache.org/thread.html/92ca1942d67a87ee6a2b4d448c621e
> > > 433f2f8aca81e4d913d8b2537e@%3Cdev.mxnet.apache.org%3E
> > > and as probably most have noticed, we have been running an experiment
> > with
> > > the PR-validation-jobs. During the past month, every PR was checked by
> > the
> > > jobs called PR-head and PR-merge. In the past, only PR-head has been
> > > executed and was the required job to pass in order to merge a PR into
> the
> > > protected master branch. Before I continue any further, I’d like to
> > explain
> > > the detailed meaning of both jobs:
> > >
> > > PR-head: The PR and its commit history is taken as-is and tested in
> > exactly
> > > the same state as in your local fork.
> > >
> > > PR-merge: The PR and its commit history are rebased on top of latest
> > master
> > > commit and thus tested as if the PR would be merged at this point in
> > time.
> > >
> > > I have noticed that many PRs are rarely rebased before a merge.
> > Considering
> > > the fast development of MXNet, this could cause serious issues:
> Imagine a
> > > PR is based on a 4 weeks old commit and accesses an API which has been
> > > modified in the meantime. PR-head would report this PR as ready to
> merge
> > as
> > > the changes, based on the 4 weeks old commit. But as soon as a
> committer
> > > merges this PR into the master branch, the master branch will suddenly
> > > report errors because this PR tries to access an API which does not
> exist
> > > anymore.
> > >
> > > Using PR-merge will reduce the chance of this happening as the PR is
> > always
> > > getting rebased on top of the master branch before it is getting
> > validated.
> > > But there is one pitfall: CI only runs if a new commit is getting
> pushed.
> > > If a PR stays untouched for a certain amount of time it still could be
> > > possible that it missed a breaking change due to the fact that CI
> hasn’t
> > > been triggered for a while, but this happens quite rarely. In order to
> > > solve this problem, we could think about introducing a job which
> > validates
> > > PRs that haven’t been run for a week, but that’s a different
> discussion.
> > > Also, if multiple PRs get merged at the same time, conflicting changes
> > (in
> > > terms of changes in one part which cause another part to fail) could be
> > > introduced – but the committers who merge the PRs usually notice two
> > > conflicting PRs. Additionally, merge conflicts in terms of changing the
> > > same lines of code on the other hand will fail fast and tell the
> > > contributor in the GitHub-webinterface that they will have to resolve
> the
> > > merge-conflicts before the PR can be validated – it couldn’t be merged
> > with
> > > merge-conflicts anyways.
> > >
> > > PR-merge is a safer choice in terms of health for the master-branch.
> > Thus,
> > > I’d like to put it up for discussion to turn off PR-head and switch the
> > > required check to PR-merge.
> > >
> > > Does anybody object?
> > >
> > > Best regards,
> > > Marco
> > >
> >
>

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