[llvm-dev] [RFC] One or many git repositories?

[David Chisnall via llvm-dev]

On 21 Jul 2016, at 07:12, Renato Golin via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
>> I don't much care which of those is chosen. I have a slight preference for
>> #1, for ease of doing things like grep/log/etc on llvm by itself, excluding
>> all the other projects. But either way seems probably fine, and an
>> improvement over multiple repositories.
> 
> I don't have a strong preference, but #1 proponents weakly convinced
> me with two arguments:
> 
> 1. it is easier to mix-and-match repositories as you like
> 
> I'd still symlink as I do today, but I can see why this would be
> interesting for off-tree users.
> 
> 2. it "makes more sense" to let Clang *use* LLVM instead of LLVM *host* Clang
> 
> this seems more preference than anything, but people that know CMake
> more than I do said it would be "easier" and I trust them. I have no
> technical arguments pro or against.
> 
> Though, I'd be fine with anything really.

First of all, thank you very much for driving this Renato.  It’s a horrible task to do and I’m very grateful that you’ve taken this on.

I would, however, like to add one argument against a single repo model.  If you look at the current LLVM GitHub repo, GitHub is tracking 806 forks.  It is tracking 595 forks for clang.  Not everyone using git for downstream development has a fork on GitHub.  In particular, GitHub does not allow private forks of public repos, so anyone who has a non-public git fork of LLVM will have done a git clone and a git push to their own private repo (on or off GitHub).  I know of about a dozen such private repos and (for some bizarre reason) most companies don’t tell me about the secret things that they’re doing with LLVM so there are undoubtedly a lot more that I don’t know about.

Conservatively, I would estimate that we have at least a thousand downstream forks of the current LLVM git repository.  Moving to a single repo model with break all of them.  It is completely unacceptable to break so many downstream consumers unless we are able to provide them with some coherent migration plan, but I have not seen anyone in the single-repo camp suggest anything.

David

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