[llvm-dev] Bumping the CMake requirement for libc++ and libc++abi

[Tom Stellard via llvm-dev]

On 03/24/2020 09:00 PM, Petr Hosek via llvm-dev wrote:
> In October, there was a discussion about updating CMake to 3.15: http://lists.llvm.org/pipermail/llvm-dev/2019-October/136295.html. No decision was made, but maybe we should revisit that proposal? If we're going to require a newer version of CMake for some subprojects, I'd prefer to bump the minimum CMake version for all of LLVM.
> 

Yes, I agree we should bump the version for all of LLVM, but I don't
think we should bump the version without a long-term cmake usage plan.
e.g. something like: After every release branch, we bump the cmake version
to whatever version of cmake is X months old.

I think the concern that this was our one chance to bump the CMake version
led to the choice of 3.15 as the next version, which would be too new for some Linux distros.
I think if we had a planned upgrade path, it would be easier for those of us that
want something really new to settle on a release that is a little bit older.

-Tom
 

> On Tue, Mar 24, 2020 at 8:11 PM Louis Dionne via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> 
>     Hi,
> 
>     The minimum CMake version currently advertised for libc++ and libc++abi is currently 3.4.3. I think the oldest version of CMake actually being tested on any builder is 3.7.0, so advertising 3.4.3 is somewhat of a lie (I'm pretty sure we're using features that require a more recent version already). However, we do need to bump it to 3.8.0 at least because CMake 3.7 doesn't know about C++17 in its compilation features, and we'll need that to build libc++ properly going forward. This will mean for bot owners:
>     1. They need to upgrade CMake on the builders to at least 3.8.0 (which is really easy), or
>     2. they can disable processing of libc++ and libc++abi's CMake files by making sure they do not appear in LLVM_ENABLE_PROJECTS
> 
>     Any objections?
> 
>     Cheers,
>     Louis
> 
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