[cfe-dev] Fwd: Raising CMake minimum version to 3.4.3

[Chris Bieneman via cfe-dev]

Actually forward to LLVM-dev because I obviously don’t know how email works…

-Chris

> Begin forwarded message:
> 
> From: Chris Bieneman via cfe-dev <cfe-dev at lists.llvm.org>
> Subject: [cfe-dev] Raising CMake minimum version to 3.4.3
> Date: April 26, 2016 at 3:01:23 PM PDT
> To: cfe-dev <cfe-dev at lists.llvm.org>, llvm-dev at lists.apple.com
> Cc: Galina Kistanova <gkistanova at gmail.com>
> Reply-To: Chris Bieneman <beanz at apple.com>
> 
> 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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