llvm dev - Mar 2020 - Bumping the CMake requirement for libc++ and libc++abi

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

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.

On Tue, Mar 24, 2020 at 8:11 PM Louis Dionne via llvm-dev <
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
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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On Tue, Mar 24, 2020 at 9:01 PM Petr Hosek via llvm-dev <
llvm-dev at lists.llvm.org> 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.
>
+1
For libc, we want 3.13 or above. Not that it matters immediately as we
don't expect llvm-libc it to be meaningfully useful at least for a
few months more. But, considering that a bump like this will take a few
months anyway, I do want to push for 3.13+.

>
> On Tue, Mar 24, 2020 at 8:11 PM Louis Dionne via llvm-dev <
> 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
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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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
> 
>     _______________________________________________
>     LLVM Developers mailing list
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>     https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
> 
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>