[llvm-dev] Git Transition status?

[Bruce Hoult via llvm-dev]

"The people most impacted by mono-repo are those who want to build just
compiler-rt"

Perhaps more accurate to say "Those who want to contribute only to
compiler-rt"?

Those who only want to build compiler-rt can check it out from a slave repo
that mirrors commits to compiler-rt in the mono-repo. Some infrastructure
is needed for this, but it's easy and automated.

On Tue, Jan 17, 2017 at 4:17 AM, Chris Lattner via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On Jan 13, 2017, at 1:37 PM, Mehdi Amini via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> The main outcome of the BoF had the dev meeting was that we agree’d that
> moving to GitHub was the best choice forward for LLVM (IIRC only one person
> in the room expressed concerned about GitHub, but he said he had personal
> grief with them and nothing specific for LLVM).
>
> The unknown that remains is: will we use a mono-repo or a multi-repo. On
> this aspect:
>
> - We got consensus at the BoF that downstream users (i.e.
> non-contributors) are not impacted by this choice, and we’re not gonna
> optimize the repository structure for them.
> - My reading of the survey is that the monorepo has a significant lead.
> - My understanding of the dynamic of the discussions and question during
> the BoF is that monorepo has a significant lead, is likely to satisfy more
> people, and has a very small number of people concerned about it. On the
> other hand many people have strong feeling about the multirepo.
>
>
> FWIW, I have spoken to a large number of people about the mono vs
> multi-repo tradeoffs, and I’m personally convinced that mono repo is the
> way to go.  For a few reasons:
>
> - Monorepo is the “natural” way to use git.  Submodules are possible to
> use, but add significant complexity.
> - The download size of a mono-repo is manageable, and seems scalable for a
> project the size of LLVM (including reasonable growth over the next 10
> years).
> - As Medhi says, according to surveys and discussions in forums like the
> LLVM Dev Meeting BoF, most people who care are in favor of mono-repo.
> - The people most impacted by mono-repo are those who want to build just
> compiler-rt.  We want these people to be happy, but they are very few in
> number, and their benefit needs to be balanced against the benefit for the
> larger community that builds llvm (and typically clang or another front
> end).
>
> Overall, it seems clear that either approach could work, but mono seems to
> win out because it is more popular and more simple. It would require tweaks
> to LLVM’s cmake system though: instead of deciding to build a subproject
> based on whether it is checked out, it should instead be based on
> configuration time flags.
>
> -Chris
>
>
>
> Considering all the current tradeoffs, it is likely that we will move-on
> with a monorepo, even if there are no guarantee or decision made at this
> point.
>
> The path forward (already engaged) is to engage a prototype phase: we’re
> building a monorepo and trying to make it usable as much as possible,
> without making any change or building anything that would commit us to a
> monorepo (for instance we’re not gonna migrate any bots to it).
>
> The goal of this prototype is that developers can start using a monorepo
> to try it, and we can evaluate how it plays in practice, outside of
> theoretical considerations. If anyone finds concerns about a given
> workflow, we can study what can be improved to address it, or maybe we’ll
> hit a wall that would show that monorepo can’t address what we think it
> will.
>
> At some point, if the experiment is conclusive, we should be able to build
> a larger majority and hopefully reach a consensus that the proposed
> prototype can be considered viable for development and start planning the
> actual committing changes.
>
> The monorepo is not totally ready yet, but you can already experience it
> (I live on day-to-day for my development, and a few other people as well),
> instructions are in the doc: http://llvm.org/docs/GettingStarted.html#for-
> developers-to-work-with-a-git-monorepo
>
> I don’t have any schedule to announce, hopefully we can make it all happen
> in 2017.
>
> Best,
>
> —
> Mehdi
>
>
> On Jan 13, 2017, at 1:07 PM, Keane, Erich via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Hi all-
> I was wondering if anyone knew what the status/schedule of the SVN to
> git/github transition was?  I thought I saw that at the November meeting it
> was agreed upon, but I'm not sure I saw any progress since?
>
> Thanks,
> Erich
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