[Openmp-dev] [cfe-dev] [RFC] Deprecate email code reviews in favor of Phabricator

Aaron Ballman via Openmp-dev openmp-dev at lists.llvm.org
Tue May 4 04:23:58 PDT 2021

On Mon, May 3, 2021 at 1:24 PM Krzysztof Parzyszek via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
> Statement:
> Our current code review policy states[1]:
> “Code reviews are conducted, in order of preference, on our web-based code-review tool (see Code Reviews with Phabricator), by email on the relevant project’s commit mailing list, on the project’s development list, or on the bug tracker.”
> This proposal is to limit code reviews only to Phabricator.  This would apply to all projects in the LLVM monorepo.  With the change in effect, the amended policy would read:
> “Code reviews are conducted on our web-based code-review tool (see Code Reviews with Phabricator).”

Personally, I am in favor of this policy for initiating code reviews,
but am opposed to it for post-commit feedback. The problem, as I see
it, is that not every change *gets* code review via Phab and the email
lists are the only place on which to provide that post-commit
feedback. This largely comes up in two ways: NFC changes and changes
made by code owners in the area of the compiler which they own. We
still need *some* mechanism by which to provide them post-commit
feedback. Currently, the way we provide that is frequently via an
email reply to the commit message on the *-commits list so that the
issue can be seen by both the patch author and the community at large.

> Current situation:
> In a recent llvm-dev thread[2], Christian Kühnel pointed out that pre-commit code reviews rarely originate via an email (most are started on Phabricator), although, as others pointed out, email responses to an ongoing review are not uncommon.  (That thread also contains examples of mishaps related to the email-Phabricator interactions, or email handling itself.)
> I don’t have specific information about post-commit reviews.  It seems like the most common form is an email reply to the auto-generated commit message, although (in my personal experience), “raising a concern” in the commit on Phabricator or commenting in the pre-commit review is usually sufficient to get author’s attention.
> We have Phabricator patches that automatically apply email comments to the Phabricator reviews, although reportedly this functionality is not fully reliable[3,4].  This can cause review comments to be lost in the email traffic.
> Benefits:
> Single way of doing code reviews: code reviews are a key part of the development process, and having one way of performing them would make the process clearer and unambiguous.
> Review authors and reviewers would only need to monitor one source of comments without the fear that a review comment may end up overlooked.
> Local Phabricator extensions would no longer be needed.
> Concerns:
> For post-commit reviews, the commenter would need to find either the original review, or the Phabricator commit (e.g. https://reviews.llvm.org/rG06234f758e19).  Those are communicated (perhaps ironically) via email, which implies that those automatic emails should remain in place.

The Phab commit message does not have any subscribers though, and so
my understanding is that comments on that Phab interface are not
communicated out to the community as a whole, which means the
community may miss out on important post-commit-review information
like general awareness of the problem, workarounds people can use
until the author corrects something, alternative ideas on how to fix
the issue, etc. Or do I misunderstand the way Phab works in this

Also, "the commenter would need to find the Phabricator commit"
concerns me -- adding extra burden on the people providing feedback
means that *some* amount of those people will struggle enough to
simply not provide that feedback. Responding to an email is about as
low as I think we can set that bar, so the current approach has better
ergonomics for giving feedback. When I look at an existing NFC commit
email (https://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20210503/368413.html),
I don't see any direct link back to the Phabricator commit, so I have
to know to get the hash and try using that with an
https://reviews.llvm.org/rG in front of it. None of the existing links
in the email get me to where I'd need to go to add my review feedback,
but hitting the Reply button in my mail client will work. Adding a
third link and telling people "click on the link in the email" means
they've got a 50/50 shot of getting the right link because one of the
links goes to GitHub where you can also add comments.

> The current policy has been in place for a long time and it’s expected that some people will continue using email for reviews out of habit or due to lack of awareness of the policy change.
> Because of the larger variety, email clients may offer better accessibility options than web browsers.
> Potential future direction:
> This section presents a potential future evolution of the review process.  Christian has conducted experiments suggesting that we can replace the XXX-commits mailing lists with notifications directly from Phabricator:
> For each of the mailing lists, we create a "project" with the same name in Phabricator, e.g. [5]. Every Phabricator user can join/leave these projects on their own.
> Everyone on these projects will receive the same email notifications from Phabricator as we have on the mailing lists. This is configured via "Herald" rules in Phabricator, as today, e.g. [7].

Tangential complaint -- our use of Herald causes some pain for me as a
list moderator because we've reached the point where Herald
automatically adds so many subscribers to a review that it gets marked
as spam for every email that is generated for the review. It's to the
point on cfe-dev where over half of the moderated emails are
consistently not spam some weeks. This delays the community receiving
the information while the patch reviewers/subscribers continue to get
it. In turn, this causes a problem where sometimes the people
subscribed to the patch say something is OK and the patch lands before
the community ever sees the review and has a chance to comment on it.
I'm wary of suggestions that involve heavier use of Herald until we
get that mailing list issue resolved.

> Users can reply to these email notifications and Phabricator will incorporate these responses with their email client, see [6] for some example emails. Quoting and markup is supported as well.
> We do NOT migrate the membership lists. Users need to sign up to the projects manually. We will send an email with instructions to the mailing lists once everything is set up.
> The current XXX-commits mailing lists will be shut down
> The timeline for the migration is to be defined.

Given how often Phabricator goes down (which is not super often, but
often enough that people know it happens), I am deeply uncomfortable
with the idea of shutting down the current *-commits mailing lists
because of the chance for data loss. Personally, I think the *-commits
lists are working well and I would prefer they be left alone.


> For experimenting, feel free to sign up to the prototype project at [5] . This project receives all commit and code review notifications.
> [1] https://llvm.org/docs/CodeReview.html#what-tools-are-used-for-code-review
> [2] https://lists.llvm.org/pipermail/llvm-dev/2021-April/150129.html
> [3] https://lists.llvm.org/pipermail/llvm-dev/2021-April/150136.html
> [4] https://lists.llvm.org/pipermail/llvm-dev/2021-April/150139.html
> [5] https://reviews.llvm.org/project/view/104/
> [6] https://reviews.llvm.org/D101432
> [7] https://reviews.llvm.org/H769
> --
> Krzysztof Parzyszek  kparzysz at quicinc.com   AI tools development
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