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

[Dean Michael Berris via llvm-dev]

> On 29 Jul 2016, at 19:19, David Chisnall via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> On 29 Jul 2016, at 05:11, Mehdi Amini via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>> 
>> What I meant by “different problem" is that “downstream users” for instance don’t need to commit, that makes their problem/workflow quite different from an upstream developer (for instance it is fairly easy to maintain a read-only view of the existing individual git repo currently on llvm.org).
> 
> I’m not convinced by this distinction.  A lot of downstream developers need to patch LLVM and we benefit when they upstream their changes.  We should not make it harder for them to do this.  To give a couple of example downstream projects, both FreeBSD and Swift have patches on LLVM / Clang in their versions that they gradually filter upstream.  Both projects have LLVM committers among their members.  If the workflow that we recommend for them makes upstreaming easy then they benefit (maintaining a fork is effort) and LLVM benefits (having people provide bug fixes makes our code better).
> 
> The workflow that we want to recommend to these people is:
> 
> - Fork the repo that you’re interested in from the LLVM GitHub organisation
> - Make your changes
> - Send pull requests for anything that you think is of interest to upstream
> 

I understand this, but why isn't "the repo you're interested in" just the megarepo (or monorepo) where every LLVM project resides?

> This makes the barrier to entry for sending code back upstream *much* lower than it currently is, to the benefit of all.  If the alternative is:
> 
> - Fork a read-only repo that you’re interested in from the LLVM GitHub organisation
> - Make your changes
> - Fork a different repo from the LLVM GitHub organisation
> - Run a script to filter some of your changes into that one
> - Send a pull request from that
> - Deal with merging between the two yourself
> 
> I strongly suspect that we’ll get a lot fewer useful contributions from downstream.  Or downstream people will just work on the monorepo and eat the cost.
> 

It isn't -- for downstream users of any of the LLVM projects, I suspect the answer will just be "instead of forking N repositories to get the benefit from these N projects, just fork the megarepo".

If I was a downstream user, this sounds like a simpler proposition *even if I'm only interested in one part of the overall LLVM project*.

> If someone is working on a downstream LLVM project and becoming familiar with our codebase, then we want them to be subtly nudging their workflow so that they eventually become LLVM contributors without noticing!
> 

Indeed. The best way I think, all things considered, is that we have a single megarepo where everything LLVM is in there. That way in case anybody wants to make any changes to any part of it, it's a simpler process _especially compared to the status quo_.

Cheers