[lldb-dev] [cfe-dev] [llvm-dev] GitHub anyone?

Thu Jun 2 09:28:56 PDT 2016

My two cents worth: our group tries very hard to avoid Git because we find it immature, hard to use, and unreliable. I know others feel differently but our vote is to stay with SVN. If distributed repositories are a priority we’d be much happier with Mercurial.

skw

> On Jun 2, 2016, at 11:21 AM, Tanya Lattner via cfe-dev <cfe-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.
> 
> -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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>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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