[llvm-dev] [RFC] High-Level Code-Review Documentation Update

Philip Reames via llvm-dev llvm-dev at lists.llvm.org
Mon Dec 2 09:52:42 PST 2019

Mehdi, David,

I think you're both pointing out exceptions rather than the general 
rule.  I tried to indicate their might be reasonable exceptions (see the 
second sentence past Mehdi's quote), but in general, particularly for 
new contributors, I think it is important we indicate something to this 
effect.  I've seen multiple new groups have issues around this.  In some 
cases, patches were reverted in post review.  In others, a bunch of time 
was sunk in a direction which turned turned out not to have wide 
agreement.  Cautioning folks to avoid that is important.

Do you have any suggestions on wording which keep the broad message, but 
make it more clear that it isn't a hard and fast rule?


On 12/2/19 7:55 AM, David Blaikie wrote:
> Yeah, +1 that people from the same organization are sometimes the only 
> ones working on a certain feature/area. (certainly I'd expect some 
> discussion about the feature in general to be discussed outside that 
> group if it's in any way contentious - but some stuff's clear enough 
> (I think I implemented debug_types years ago, likely with only Eric's 
> approval, both of us being at Google (probably many DWARF features 
> were added/done this way, to be honest - maybe some could've done 
> witha  bit of broader discussion, but I don't think either of us were 
> "rubber stamping" the other's work (if anything I'm harder on my 
> "friends" to be honest... :/ )))
> On Wed, Nov 27, 2019 at 10:27 PM Mehdi AMINI via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>     On Sat, Nov 16, 2019 at 5:56 PM Mehdi AMINI <joker.eph at gmail.com
>     <mailto:joker.eph at gmail.com>> wrote:
>         +1 in general, and Philip has good suggestions as well!
>         -- 
>         Mehdi
>         On Sat, Nov 16, 2019 at 8:37 AM Philip Reames via llvm-dev
>         <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>             + 1 in general, a couple of suggestions
>             On 11/14/19 7:46 PM, Finkel, Hal J. via llvm-dev wrote:
>             > Hi, everyone,
>             >
>             > I've been fielding an increasing number of questions
>             about how our
>             > code-review process in LLVM works from people who are
>             new to our
>             > community, and it's been pointed out to me that our
>             documentation on
>             > code reviews is both out of date and not as helpful as
>             it could be to
>             > new developers.
>             >
>             > http://llvm.org/docs/DeveloperPolicy.html#code-reviews
>             >
>             > I would like to compose a patch to update this, but
>             before I do that, I
>             > want to highlight some of my thoughts to get feedback.
>             My intent is to
>             > capture our community best practices in writing so that
>             people new to
>             > our community understand our processes and expectations.
>             Here are some
>             > things that I would like to capture:
>             >
>             >   1. You do not need to be an expert in some area of the
>             compiler to
>             > review patches; it's fine to ask questions about what
>             some piece of code
>             > is doing. If it's not clear to you what is going on,
>             you're unlikely to
>             > be the only one. Extra comments and/or test cases can
>             often help (and
>             > asking for comments in the test cases is fine as well).
>             Authors are encouraged to interpret questions as reasons
>             to reexamine
>             the readability of the code in question. Structural
>             changes, or further
>             comments may be appropriate.
>             >
>             >   2. If you review a patch, but don't intend for the
>             review process to
>             > block on your approval, please state that explicitly.
>             Out of courtesy,
>             > we generally wait on committing a patch until all
>             reviewers are
>             > satisfied, and if you don't intend to look at the patch
>             again in a
>             > timely fashion, please communicate that fact in the review.
>             >
>             >   3. All comments by reviewers should be addressed by
>             the patch author.
>             > It is generally expected that suggested changes will be
>             incorporated
>             > into the next revision of the patch unless the author
>             and/or other
>             > reviewers can articulate a good reason to do otherwise
>             (and then the
>             > reviewers must agree). If you suggest changes in a code
>             review, but
>             > don't wish the suggestion to be interpreted this
>             strongly, please state
>             > so explicitly.
>             >
>             >   4. Reviewers may request certain aspects of a patch to
>             be broken out
>             > into separate patches for independent review, and also,
>             reviewers may
>             > accept a patch conditioned on the author providing a
>             follow-up patch
>             > addressing some particular issue or concern (although no
>             committed patch
>             > should leave the project in a broken state). Reviewers
>             can also accept a
>             > patch conditioned on the author applying some set of
>             minor updates prior
>             > to committing, and when applicable, it is polite for
>             reviewers to do so.
>             >
>             >   5. Aim to limit the number of iterations in the review
>             process. For
>             > example, when suggesting a change, if you want the
>             author to make a
>             > similar set of changes at other places in the code,
>             please explain the
>             > requested set of changes so that the author can make all
>             of the changes
>             > at once. If a patch will require multiple steps prior to
>             approval (e.g.,
>             > splitting, refactoring, posting data from specific
>             performance tests),
>             > please explain as many of these up front as possible.
>             This allows the
>             > patch author to make the most-efficient use of his or
>             her time.
>             If the path forward is not clear - because the patch is
>             too large to
>             meaningful review, or direction needs to be settled - it
>             is fine to
>             suggest a clear next step (e.g. landing a refactoring)
>             followed by a
>             re-review.  Please state explicitly if the path forward is
>             unclear to
>             prevent confusions on the part of the author.
>             >
>             >   6. Some changes are too large for just a code review.
>             Changes that
>             > should change the Language Reference (e.g., adding new
>             > target-independent intrinsics), adding language
>             extensions in Clang, and
>             > so on, require an RFC on *-dev first. For changes that
>             promise
>             > significant impact on users and/or downstream code
>             bases, reviewers can
>             > request an RFC (Request for Comment) achieving consensus
>             before
>             > proceeding with code review. That having been said,
>             posting initial
>             > patches can help with discussions on an RFC.
>             >
>             > Lastly, the current text reads, "Code reviews are
>             conducted by email on
>             > the relevant project’s commit mailing list, or
>             alternatively on the
>             > project’s development list or bug tracker.", and then
>             only later
>             > mentions Phabricator. I'd like to move Phabricator to be
>             mentioned on
>             > this line before the other methods.
>             >
>             > Please let me know what you think.
>             >
>             > Thanks again,
>             >
>             > Hal
>             A couple of additional things:
>             Only a single LGTM is required.  Reviewers are expected to
>             only LGTM
>             patches they're confident in their knowledge of. Reviewers
>             may review
>             and provide suggestions, but explicitly defer LGTM to
>             someone else.
>             This is encouraged and a good way for new contributors to
>             learn the code.
>             There is a cultural expectation that at least one reviewer
>             is from a
>             different organization than the author of the patch. 
>     Actually, while I'm OK with the other suggestions, I didn't pay
>     attention to this one originally.
>     I'm very concerned about this: this looks like an assumption of
>     bad faith or malice in the review process, and I find this
>     unhealthy if it were part of the "cultural expectation". Moreover
>     there are many areas of the compiler where there aren't many
>     people available to review changes.
>     I personally never really paid attention to who is the
>     author/reviewer of a patch from an organizational point of view, I
>     haven't perceived this culture of looking into affiliation so far.
>     I never got the impression that reviewer were more difficult with
>     me than they would be with others.
>     There have been many patches that I reviewed that originated from
>     other people from the same company as mine (back when I was at
>     Apple mostly). The notion of "organization" is blurry: frequently
>     this involved people from different teams inside the same company,
>      are they part of "the same organization"? Some of these people I
>     have never even ever met or never heard of them before reviewing a
>     patch (sometimes I don't even realize since there is a Phabricator
>     pseudo and not everyone is using their business email here).
>     -- 
>     Mehdi
>             If that's not
>             possible, care should be taken to ensure overall direction
>             has been
>             widely accepted.
>             Post commit review is encouraged via either phabricator or
>             email.  There
>             is a strong expectation that authors respond promptly to
>             post commit
>             feedback and address it.  Failure to do so is cause for
>             the patch to be
>             reverted.  If substantial problems are identified, it is
>             expected that
>             the patch is reverted, fixed offline, and then recommitted
>             (possibly
>             after further review.)
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