[cfe-dev] Raising CMake minimum version to 3.4.3

[James Y Knight via cfe-dev]

+1. Cmake is completely trivial to install yourself. You don't even need to
install it, even, you can just run it from the build directory. IMO, if
there's any reason why a newer version would be useful, it's totally worth
just requiring an upgrade instead of spending time trying to overcome
limitations of the old version.

Perhaps the buildbots could just ensure that a recent cmake is built, as
the first build step, to avoid having to coordinate with all the bot
maintainers.

On Tue, Apr 26, 2016 at 6:01 PM, Chris Bieneman via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hello llvm-dev and cfe-dev,
>
> I want open up the discussion of upgrading our minimum required CMake
> version.
>
> In the past when we’ve discussed this one of the major reasons for not
> moving forward was that the Ubuntu LTS release was on CMake 2.8.12.x. A few
> days ago Ubuntu 16.04, the new LTS, was released, and it contains CMake
> 3.5.1.
>
> I have a couple of motivations for this, the biggest of which is that I’ve
> hit a wall trying to overcome some limitations in the CMake ExternalProject
> module which I can’t get past without being on CMake 3.4 or newer. These
> limitations make using ExternalProject to build the LLVM test-suite and
> runtime libraries (compiler-rt, libcxx, etc) difficult.
>
> The other big motivation that I have for this is the ability to cleanup
> code. We have a lot of CMake code that checks CMAKE_VERSION and enables and
> disables features used on the version. None of the places where we
> currently have CMAKE_VERSION checks should impact build correctness, but
> most people don’t realize that if you’re using Ninja your build will be
> faster on a newer CMake than on an older one. It would be nice if we just
> pushed the bar up and could remove a bunch of those conditionals.
>
> To do this we need bot maintainers to update their CMake installations, so
> we need some consensus that (1) we want to do this and (2) what a
> reasonable timeline for doing it is.
>
> What I’d like to do is raise the minimum version for all LLVM projects to
> CMake 3.4.3 at the end of May. Setting the date at the end of May gives bot
> maintainers and developers lots of time to update, and CMake 3.4.3 is the
> last CMake 3.4 release and it is widely available. For reference here’s a
> list of linux distributions and their CMake versions:
>
> Ubuntu Wily -> 3.2.2
> Ubuntu Xenial -> 3.5.1
> Ubuntu Yakkety -> 3.5.1
> Debian jessie -> 3.0.2
> Debian stretch -> 3.5.1
> Debian sid -> 3.5.2
> FreeBSD 10.2 -> 3.5.0
> FreeBSD HEAD -> 3.5.2
>
> Feedback?
>
> Thanks,
> -Chris
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>
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