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

David Chisnall via llvm-dev llvm-dev at lists.llvm.org
Fri Jul 29 02:19:05 PDT 2016

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

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.

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!


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