[lldb-dev] [llvm-dev] [RFC] Deprecate email code reviews in favor of Phabricator

Krzysztof Parzyszek via lldb-dev lldb-dev at lists.llvm.org
Tue May 4 06:30:57 PDT 2021

I'm opposed to separating the pre- and post-commit reviews.  One of the goals of this proposal is to have the entire review history in one place, and using a combination of email and Phabricator would prevent that.  If I want to find out why a commit has been reverted, I have to search the post-commit emails to see what happened.  I guess one could argue that pre- and post-commit reviews could happen on different pages (Dxxx vs rGxxx), but, in my view, that is still better than emails.  The two concerns I have about post-commit reviews on Phabricator are that

  1.  People will keep doing it via email, because there is no mechanism (short of making the -commits lists read-only) that would actively inform them about the change in policy.
  2.  It takes a bit of manual work to get to the rG page for the commit, and if the commit message doesn't include the link to the pre-commit review, the corresponding D page may be hard to locate.

Regarding point (2), I'm hoping that something can be done in Phabricator to make the post-commit reviews easier: it may be as simple as sending the commit message to a list of subscribers.

Krzysztof Parzyszek  kparzysz at quicinc.com<mailto:kparzysz at quicinc.com>   AI tools development

From: Philip Reames <listmail at philipreames.com>
Sent: Monday, May 3, 2021 5:08 PM
To: Krzysztof Parzyszek <kparzysz at quicinc.com>; llvm-dev <llvm-dev at lists.llvm.org>
Cc: clangd-dev at lists.llvm.org; openmp-dev at lists.llvm.org; lldb-dev at lists.llvm.org; cfe-dev at lists.llvm.org; libcxx-dev at lists.llvm.org; flang-dev at lists.llvm.org; parallel_libs-dev at lists.llvm.org
Subject: [EXT] Re: [llvm-dev] [RFC] Deprecate email code reviews in favor of Phabricator

In my view, this email is really too different topics.  Given that, my response is split into two parts.

First, should we make phabricator our default for code review?  I am not opposed to this.  I don't particular support it either, but I would not spend time arguing against it.  I would suggest that we re-frame the proposal to distinguish precommit and post commit review - with only the former moving to phabricator.  I have not seen post-commit done successfully on phabricator to date in any wide spread manner.

Second, should we consider retiring llvm-commits and the other mailing lists?  My gut response is a flat out NO!!!!  What we have works.  I am highly reluctant to run the risk of breaking our existing processes - which for all their problems mostly work - for the, to me, seemingly very minimal value obtained by moving away from email discussion.  Post commit review in email works.  I strongly suspect that if you try to change that, you will either simply drive out post commit review discussion (bad idea!) or discussions will move to private email exchanges (bad idea!).  I'm open to being convinced here, but the burden of proof is high.  The risk we'd be talking about with such a transition is immense.

On 5/3/2021 10:24 AM, Krzysztof Parzyszek via llvm-dev wrote:


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)."

Current situation:

  1.  In a recent llvm-dev thread[2], Christian K├╝hnel 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.)
  2.  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.
  3.  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.


  1.  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.
  2.  Review authors and reviewers would only need to monitor one source of comments without the fear that a review comment may end up overlooked.
  3.  Local Phabricator extensions would no longer be needed.


  1.  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.
  2.  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.
  3.  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:

  1.  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.
  2.  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].
  3.  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.
  4.  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.
  5.  The current XXX-commits mailing lists will be shut down
  6.  The timeline for the migration is to be defined.
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<mailto:kparzysz at quicinc.com>   AI tools development


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