Cherry-pick proposal

[Nicola Tuveri]

I can agree it is a good idea to always require backport as a separate PR,
with the following conditions:
- unless it's a 1.1.1 only issue, we MUST always wait to open the
backport-to-111 PR until after the master PR has been approved and merged
(to avoid splitting the discussions among different PRs, which make review
and revisiting our history very hard)
- trivial documentation changes, such as fixing typos, can be exempted

It must be clear that although things have changed a lot in the inner
plumbings, we have so far managed to keep crypto implementations very much
in sync between 1.1.1 and master, by applying the policy of "first merge to
master, then possibly backport".

What I am afraid of in Bernd's proposal, and recent discussions, is that
committers might be tempted to open PRs changing implementations against
1.1.1 first (to avoid frequent rebases due to unrelated changes) and let
the `master` PR stagnate indefinitely because it feels like too much hassle
to keep up with the development pace of master if your PR collaterally
changes certain files.

An example of what can go wrong if we open a 1.1.1 PR concurrently with a
PR for master can be seen here:
- `master` PR: https://github.com/openssl/openssl/pull/10828
- `1.1.1` PR: https://github.com/openssl/openssl/pull/11411

I highlight the following problems related to the above example:
- as you can see the `1.1.1` has been merged, even though the `master` one
has stalled while discussing which implementation we should pick. (this was
my fault, I should have applied the `hold` label after stating that my
approval for 1.1.1 was conditional to approving the `master` counterpart)
- discussion that is integral part of the decision process was split among
the 2 PRs, with over 40 comments each
- there is no clear link between the `master` PR and the `1.1.1` PR for the
same feature (this makes it very difficult to review what is the state of
the "main" PR, and if we or someone else in some months or years needs to
go check why we did things the way we did, will have a hard time connecting
the dots)

I also think that the proposal as written is a bit misleading: I would very
like to keep seeing in 1.1.1 a majority of commits cherry-picked from
commits merged to master, with explicit tags in the 1.1.1 commit messages
(this helps keeping the git history self-contained without a too strong
dependency on GitHub).
I would rephrase the proposal as follows:

    Merge to 1.1.1 should only happen after approval of a dedicated PR
targeting the OpenSSL_1_1_1-stable branch.

Potential amendments that I'd like the OTC to consider are:
a) before the end of the sentence add ", with the optional exclusion of
trivial documentation-only changes"
b) after the end of the sentence add "In composing backport pull requests,
explicit cherry-picking (`git cherry-pick -x`) of relevant commits merged
to `master` or another stable branch is recommended and encouraged whenever
possible."
c) adopt a more general statement:

    Merge to any stable branch should only happen after approval of a
dedicated PR targeting specifically that branch.




So, in summary, I would agree with the proposal, as I definitely think
Bernd has a good point about running the 1.1.1 CI for things we think
should be backported, but requires careful consideration of additional
requirements to avoid duplicating review efforts, splitting discussions
that should be kept together, or disrupting our processes making 1.1.1 and
master diverge more than necessary.


Cheers,


Nicola

On Wed, 29 Apr 2020 at 14:08, Matt Caswell <matt at openssl.org> wrote:

>
> The OTC have received this proposal and a request that we vote on it:
>
> I would like to request that we do not allow cherry-picks between master
> and 1.1.1-stable because these two versions are now very different, if a
> cherry-pick succeeds, there is no guarantee that the result will work.
> Because we have no CI for the cherry-pick. If a cherry-pick is needed, a
> new PR for 1.1.1 should be done and approved independently.
>
> Before starting a vote I'd like to provide opportunity for comments, and
> also what the vote text should be.
>
> Thanks
>
> Matt
>
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