[llvm-dev] RFC: Updating to CMake 3.15.0

[Stefan Gränitz via llvm-dev]

Strong agree in general. A number of policy proposals were discussed
already. The thread still reads like a split between supporters and
opponents?

In my opinion the update process on build bots was not discussed enough.
If we choose a version and then see that it's gonna be a problem with
many build bots, this will be a blocker and potential time sink for
maintainers right? Should we do it first and then bump the CMake version?

Here's a proposal that gives build bot maintainers enough time:
(1) Once a new LLVM release version branches: start updating CMake to
latest available binary releases on all build bots
(2) Once the new LLVM version is released: bump minimum CMake
requirement on master to the lowest common denominator of the (updated)
build bots

What do you think?

On 29/10/2019 18:10, Chris Bieneman via llvm-dev wrote:
> At the LLVM Developer Meeting on October 23rd we held a CMake roundtable. One of the items we discussed was adopting a more regular timeline for CMake upgrades. During the roundtable there was overwhelming support for upgrading CMake, and support for treating CMake differently than how we treat upgrading host compilers.
>
> Historically we've taken into account recent versions of Visual Studio, Xcode and Linux distribution long term support packages when deciding what CMake version to require. While this does work, it has held us to old versions of CMake for long periods of time.
>
> During the roundtable we discussed that the amount of effort involved in updating to a modern CMake is more or less the same regardless of what version we choose. We believe this to be true because most OS package managers have older versions, like the Ubuntu 18.04 LTS which has CMake 3.10.2 which was released January 18, 2018. Additionally CMake.org provides binary and source downloads, and building CMake from source has lower system requirements than LLVM and is very simple.
>
> With all of this in mind at the roundtable we decided to propose raising the minimum required CMake version for all LLVM sub-projects to 3.15.0. Assuming there are no objections to this proposal, I propose a cut-over date of December 2, 2019.
>
> Thanks,
> -Chris
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