[llvm-dev] Upgrading LLVM's minimum required CMake version

Thu Jul 16 18:20:31 PDT 2020

Please, no more waiting on CMake versions in distro LTS releases. We have
been *way* too conservative already, waiting this long.

Downloading and building a local copy of cmake is trivial. You don't even
need to install it. Anyone who is developing and building LLVM can
definitely manage it. Not only that, kitware even has an official apt
repository -- you can install a deb if installing that seems easier for you
(https://apt.kitware.com/).

On Thu, Jul 16, 2020 at 8:05 PM Jessica Clarke via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On 30 Jun 2020, at 16:04, Louis Dionne via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >> On Apr 8, 2020, at 13:06, Louis Dionne <ldionne at apple.com> wrote:
> >>> On Apr 2, 2020, at 10:19, Louis Dionne via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >>>
> >>> Okay, so we've had some discussion on this thread, and although some
> people (including me) would like a more aggressive policy, I believe the
> following will not get any objection (based on the thread). On April 23rd
> 2020, Ubuntu 20.04 LTS will ship with CMake 3.16.x. This will make the
> lower bound for LTS distributions be 3.13.4, and so I suggest we upgrade to
> that. Here's a proposed process:
> >>>
> >>> 1. Immediately add a CMake warning in <root>/llvm/CMakeLists.txt
> saying that CMake 3.13.4 will be the new minimum version starting with LLVM
> 12.0.0, and mentioning the versions used in various LTSes.
> >>> 2. Immediately send a courtesy heads-up email to all build-bot owners
> telling them about the upcoming change.
> >>> 3. Right after we branch off the release branch for LLVM 11.0.0 (the
> next one), make the minimum CMake version required be 3.13.4.
> >>> 4. Iterate on (3) until all bots are migrated.
> >>> 5. Send a message to the list saying the bump is complete. At that
> time, projects are free to start using features from 3.13.4.
> >>>
> >>> Unless someone else absolutely wants to bite the bullet, I volunteer
> to do the above steps.
> >>
> >> Ok, so the thread has kept going, but AFAICT all the discussion is
> about a policy for "automatic" upgrades. So I've went ahead and did the
> first two steps of the above algorithm:
> >>
> >> (1) Review at https://reviews.llvm.org/D77740
> >> (2) Email sent to the owners of all build slaves listed on
> http://lab.llvm.org:8011/buildslaves
> >>
> >> Just to reiterate, this means that as soon as we branch LLVM 11.0.0
> (the NEXT release), CMake 3.13.4 will be the minimum required version.
> >
> > Hi,
> >
> > Just a heads up that about two weeks from now, we should be branching
> for the LLVM 11.0.0 release. Right after we branch, I will implement steps
> (3) and (4) of the algorithm described above, which is to make the minimum
> CMake version required be 3.13.4. I will do this by checking-in this patch:
> https://reviews.llvm.org/D78646.
> >
> > That patch will cause errors whenever the CMake version is less than
> 3.13.4 -- I will then revert and re-apply this patch until all build bots
> have upgraded to a sufficient CMake. The patch was crafted to be minimal
> and revert-friendly. Note that build bot owners have already been contacted
> in March and pinged several times again for those who had not yet upgraded.
> At this time, I think only 1-2 bots have not upgraded.
> >
> > Once everyone has upgraded, I will then apply this patch:
> https://reviews.llvm.org/D78648. That patch marks the minimum CMake
> version required as being 3.13.4 throughout the monorepo in a slightly more
> invasive but definitive way. Once that's all done, I'll report to the list
> that the version bump is complete and we can all start using modern CMake
> features.
> >
> > Cheers,
> > Louis
>
> I missed this entire discussion but would like to chime in. All of our
> department's machines run on Ubuntu 18.04 as standard. I suspect the same
> is true across a large number of organisations, as Ubuntu is a very popular
> distribution, and the 18.04 LTS is still widely supported by most projects.
> Whilst Ubuntu 20.04 has been released for a couple of months, it's going to
> be a while until everyone has updated. In fact, it isn't yet *officially
> supported* to upgrade from 18.04 to 20.04, as you have to wait for the
> first point release for that, due in August. So as far as Canonical are
> concerned, if you installed 18.04 LTS, you should still be on that, and
> 20.04 isn't ready for those people quite yet. That's a lot of people
> affected who may not be following llvm-dev but will suddenly find
> themselves in need of a custom CMake.
>
> I would urge people to reconsider this move. I can see the attraction of
> moving to the latest CMake, but we've managed just fine so far, do we
> really need to move to the latest and greatest right now? Ditching support
> for 18.04 in a year's time would seem reasonable, but expecting everyone to
> have moved over when it's not yet officially supported after just 3 months
> is not, and forcing everyone on those distributions to build their own copy
> of CMake just for LLVM is annoying (sure, I'm perfectly capable of doing
> it, but it's still a nuisance that aggravates me). I'd suggest waiting at
> least until 20.04.1 has been released, so waiting until the next release
> cycle would allow that and give around 6 months for people to update, if
> not until the release cycle after that (though that may be a harder pill
> for some members to swallow). But we could at least bump to 3.10.2 in the
> meantime.
>
> Jess
>
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