[llvm-dev] GitHub anyone?

Tanya Lattner via llvm-dev llvm-dev at lists.llvm.org
Thu Jun 2 16:28:36 PDT 2016

> On Jun 2, 2016, at 12:18 PM, Mehdi Amini <mehdi.amini at apple.com> wrote:
>> On Jun 2, 2016, at 9:21 AM, Tanya Lattner via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>> I personally find this email thread very hard to follow and read (this isn’t anyones fault.. its just a lot of replies). I am sure others do as well. I think it would be good to have a form/survey of some sort that can get feedback from users such as: who they are, how they use LLVM/contributions/etc,  if they are pro-github move, how it impacts them, etc. People could then submit their feedback in an organized way and we could get a better idea of how the community feels on the topic. 
>> I am happy to try to set something like this up.
> I don't think it is a good idea to set this up like that without having a well defined plan first.
> My idea is rather that we should first try to see what is doable in term of server-side hook and integration so that the "poll" is not about naked "svn vs git", but about "svn vs git-with-this-server-side-setup-that-preserve-our-workflow".

Sure, I am fine with flushing out those details out. Just an idea to get a better idea of the consensus when the time comes.


> -- 
> Mehdi
>> -Tanya
>>> On Jun 2, 2016, at 8:48 AM, Renato Golin via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>> A little summary...
>>> After a lot of discussion, I think we converged to a few issues that
>>> we need to solved before we finally decide to move.
>>> Firstly, the responses were overwhelmingly positive (I counted 20 of
>>> the ~25 people strongly supporting and another 2~3 weakly supporting).
>>> This is a good indication that the move could be very beneficial to
>>> the community as a whole, including downstream infrastructure, not
>>> just the reduction in upstream infrastructure admin costs.
>>> But that doesn't mean we have cleared up all the issues...
>>>  The benefits I gathered from the thread:
>>> * Infrastructure admin (not just server costs) is too expensive.
>>> We're not sysadmins and maintaining all the tools is a full time job.
>>> Volunteering works for odd problems, not for production services.
>>> Furthermore, most of the infrastructure we need is covered by
>>> GitHub/Lab/BB for free, on a scale that we would not have, even with a
>>> full time sysadmin. Gratis.
>>> * Having one official repository instead of two is beneficial to most
>>> developers. A lot of people (most people replying on this thread), use
>>> Git in addition to SVN. Git also seems to be used more on validation
>>> infrastructure than SVN (no example was put forward on this thread, at
>>> least), due to the simplicity of controlling the repository and the
>>> tools available. Reports of how teams decided to script Git to have
>>> linear behaviour instead of falling back to SVN are enlightening.
>>> * Git developer tooling is a growing trend, while SVN tooling is
>>> dying. This is not just about GUIs, but repository management (GitHub,
>>> GitLab, BitBucket, etc versus SourceForge), bisects, branches,
>>> remotes, hooks, workdir, submodules and all the new development seem
>>> to be done on Git nowadays, not SVN. Windows may be an odd one related
>>> to GUIs, but Visual Studio has Git integration and I hear it's similar
>>> to the other MSVC VCSs. GitHub's desktop interface seems pretty cool,
>>> too.
>>> * Web repositories make it *a lot* easier to create add-hoc pull
>>> requests by non-developers, which could boost the number of
>>> contributions and future contributors, as well as external projects
>>> using LLVM components.
>>> * GitHub's SVN RW interface has been reported to work well for
>>> simpler projects, but we need a more thorough examination before
>>> declare it good enough for our purposes.
>>> * All reports on the thread pointed that downstream infrastructure is
>>> already using Git, so that's one less problem to worry about if we do
>>> move.
>>>  The issues that were raised:
>>> * Co-dependent patches already break buildbots, but the sequential ID
>>> helps us identify and ignore. They will continue to break, even if we
>>> use git sub-modules, so that doesn't change much, but it will be
>>> harder to spot the issue. Server side hooks may help, as well as
>>> sub-modules.
>>> * Windows tooling may be an issue. There's a separate thread handling
>>> that part, so I won't cover it here. But I have to say it wasn't by a
>>> long shot a resonant problem. It may also have some problem with
>>> symlinks and in-tree checkouts (when interacting with llvm-projects
>>> and sub-modules).
>>> * Sub-modules may help with a lot of the current relationship we have
>>> inside the SVN repo, but it also has some problems. Namely they:
>>> - require a modern version of git (1.7/1.9), but that's 2013 onward.
>>> - may need additional server side scripting, but we can keep that
>>> in another repo to control it.
>>> - won't replace SVN's monotonic IDs, but do we *really* need them?
>>> Sub-modules have a bad fame, I gather, but people in the thread
>>> reported success on using it to build validation and release
>>> infrastructure as well as doing bisects, checking out code, etc. We
>>> probably need some documentation on how to do these things, as well as
>>> some scripts to help people work out the dependencies (or use them).
>>> * GitHub/Lab/BB are not perfect. They have some interface issues, but
>>> nothing more serious than we already have on our current
>>> infrastructure. We'll probably have to keep Bugzilla (as GitHub's own
>>> is really poor), but we can replace all our repos (SVN, Git),
>>> visualisation tools (ViewVC, Klaus) and Phabricator.
>>> Of all those issues, Windows tooling is a minor problem that shouldn't
>>> impact decision that much and sub-modules need a lot of ironing out to
>>> be considered good enough. My *personal* take away is that sub-modules
>>> (or an alternative server side solution) is the only strong technical
>>> issue we need to solve before we decide.
>>> How does a move look like?
>>> If we decide to move, the proposed schedule is something like this:
>>> STEP #1 : Pre Move
>>> 0. Update docs to mention the move, so people are aware the it's going on.
>>> 1. Register an official GitHub project with the LLVM foundation.
>>> 2. Setup another (read-only) mirror of llvm.org/git at this GitHub project
>>> 3. Make sure we have a la llvm-project-submodules setup in the
>>> official account. (Optional or necessary for the buildbots?)
>>> 4. Make sure bisecting with llvm-project-submodules is a good experience
>>> 5. Make sure no one has any blocker
>>> STEP #2 : Git Move
>>> 6. Update the buildbots to pick up updates and commits from the
>>> official git repository
>>> 7. Update Phabricator to pick up commits from the official git repository
>>> 8. Tell people living downstream to pick up commits from the official
>>> git repository
>>> 9. Give things time to settle. We could play some games like disabling
>>> the svn repository for a few hours on purpose so that people can test
>>> that their infrastructure has really become independent of the svn
>>> repository.
>>> ... Until this point nothing has changed for developers, it will just
>>> boil down to a lot of work for buildbot and other infrastructure
>>> owners ...
>>> STEP #3: Write Access Move
>>> 10. Collect peoples GitHub account information, give them push access.
>>> Ideally while still locking the GitHub repository somehow...
>>> 11. Switch SVN repository to read-only and allow pushes to the GitHub
>>> repository.
>>> 12. Mirror Git to SVN.
>>> STEP #4 : Post Move
>>> 13. Archive the SVN repository, if GitHub's SVN is good enough.
>>> 14. Review and update *all* LLVM documentation.
>>> 15. Review website links pointing to viewvc/klaus/phab etc. to point
>>> to GitHub instead.
>>> This is an adapted version of Matthias' and Mehdi's proposal, and it's
>>> not a final version in any way, but these are the basic things we need
>>> to worry about.
>>>  Steps from here...
>>> Aaron has started the Windows tooling thread, and if you have any
>>> comments, please follow from there. I suggest sub-modules supporters
>>> to start another thread to iron that out separately.
>>> Once those issues are resolved, we shall start another thread to
>>> finally take a decision to move or not.
>>> Thanks everyone!
>>> cheers,
>>> --renato
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