[llvm-dev] [cfe-dev] GN build roundtable summary; adding GN build files to the repo

[Alex Bradbury via llvm-dev]

On Thu, 1 Nov 2018 at 14:14, Nico Weber via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
>
> Lots of feedback! Sounds like several people are interested in this, which is cool.
>
> Trying to address a few points here:
>
>  > f these files exist in the repo, I could imagine that reviewers will
> > reject patches that might/likely break the gn files.
>
> I will make the language in https://reviews.llvm.org/D53944 stronger. Reviewers should not ask for this. If it helps, we could put the gn build files into a directory called "experimental" or similar.
>
> > Do you think there will be some point in time that these files will be
> > out of 'experimental' status?
>
> Not anytime soon.
>
> > Some folks who don't like GN or don't see the point.
>
> That's fine, see first sentence in my mail :-)
>
> > my strong preference would be to accompany that with a plan to phase cmake out.
>
> I very strongly don't think this should happen. cmake does many things right, for example running on all the platforms under the sun and supporting very long-tail issues. By saying "cmake stays the main build system" there's a long list of things we don't need to worry about. If in a few years GN can build on all the platforms under the sun, everything in LLVM works in the GN build, and everyone happens to use it, we could discuss this at that point, but in my opinion this is extremely unlikely to happen. If this is a requirement, I guarantee this thread will fizzle out. Also, I'm very much not interested in pushing for moving llvm off cmake personally.

I think presence in distro repositories is also a barrier. Most
distributions have appropriate cmake and ninja packages, but not gn.
Obviously pre-built binaries help, but it's an extra barrier.

> > the gn bots should be private, not public
>
> I agree that no bots on the official LLVM waterfall (http://lab.llvm.org:8011/console) should use GN. They would be off-waterfall bots that don't email you and that you wouldn't know about if you didn't go looking for them. They wouldn't even run on LLVM's buildbot instance.

There's a "staging" buildbot instance for exactly this sort of thing
http://lab.llvm.org:8014/ - no emails will be generated. Ideally it
would generate emails for the bot owner, but unfortunately neither I
or Dylan McKay have managed to do that.

I'm sorry I missed your lightning talk. I don't have a strong opinion
one way or another on whether gn build files belong in or out-of-tree,
but I appreciate being introduced to it - it looks like it has a lot
to offer.

Best,

Alex