llvm dev - Feb 2015 - [LLVMdev] [RFC] Raise minimum required CMake version to 3.0

> On Feb 24, 2015, at 8:45 AM, Tobias Grosser <tobias at grosser.es>
wrote:
> 
> On 09.02.2015 20:12, Chris Bieneman wrote:
>> It came up on another thread that our current minimum required CMake
version 2.8.8, has some bugs that cause issues when building with MSVC + Ninja,
and one potential solution was to raise the minimum required version of CMake.
>> 
>> CMake 3.0 is now 6 months old and CMake 3.1 has been released. I would
like to propose moving our minimum required CMake version to 3.0.
>> 
>> I’ve attached patches to enforce the change in case anyone wants to
test it out.
>> 
>> Thoughts/comments/concerns/objections?
> 
> Hi Chris,
> 
> this update broke my cmake LLVM+Polly buildbot (to my knowledge most other
bots use autoconf). I reverted this temporarily to avoid the buildbot noise
(this comes a little late, as I was traveling the last days).
Actually at this point I think most bots are on CMake. The green dragon bots are
all CMake, Galina and Takumi’s bots are at least partially on CMake.
> 
> The buildbot is based on the latest debian stable (wheezy), which comes
with cmake 2.8.9. Is 2.8.9 enough to fix the bug?
No. The bug requires 2.8.12.1. I really wanted 3.0, but Chandler requested
2.8.12.2 because it was the version in the latest Ubuntu LTS.

I’m going to put on my “unpopular opinion” hat for a second. I don’t think it is
reasonable for us to limit our CMake version to the lowest common denominator of
all Linux distributions. I really think the Linux developers should just do what
I do on OS X and build it from source. Building CMake is really simple and fast.

This is kinda a bit of a sore point for me because it turns out that our CMake
goop for cross-compiling is pretty nasty, and there are features in CMake 3.x
that make it a lot better. Unfortunately using the new features while supporting
CMake 2.8.x would only make our goop goopier.
> 
> Also, could we just limit the cmake version on windows builds? In the end
on linux cmake 2.8.9 works great.
I don’t use Windows, but I really don’t like this proposal because it will
increase maintenance if we’re supporting different versions of CMake on
different platforms (hence why I haven’t started using CMake 3.x features).

-Chris
> 
> Cheers,
> Tobias

> On Feb 24, 2015, at 9:33 AM, Chris Bieneman <beanz at apple.com>
wrote:
> 
>> 
>> On Feb 24, 2015, at 8:45 AM, Tobias Grosser <tobias at
grosser.es> wrote:
>> 
>> On 09.02.2015 20:12, Chris Bieneman wrote:
>>> It came up on another thread that our current minimum required
CMake version 2.8.8, has some bugs that cause issues when building with MSVC +
Ninja, and one potential solution was to raise the minimum required version of
CMake.
>>> 
>>> CMake 3.0 is now 6 months old and CMake 3.1 has been released. I
would like to propose moving our minimum required CMake version to 3.0.
>>> 
>>> I’ve attached patches to enforce the change in case anyone wants to
test it out.
>>> 
>>> Thoughts/comments/concerns/objections?
>> 
>> Hi Chris,
>> 
>> this update broke my cmake LLVM+Polly buildbot (to my knowledge most
other bots use autoconf). I reverted this temporarily to avoid the buildbot
noise (this comes a little late, as I was traveling the last days).
> 
> Actually at this point I think most bots are on CMake. The green dragon
bots are all CMake, Galina and Takumi’s bots are at least partially on CMake.
> 
>> 
>> The buildbot is based on the latest debian stable (wheezy), which comes
with cmake 2.8.9. Is 2.8.9 enough to fix the bug?
> 
> No. The bug requires 2.8.12.1. I really wanted 3.0, but Chandler requested
2.8.12.2 because it was the version in the latest Ubuntu LTS.
> 
> I’m going to put on my “unpopular opinion” hat for a second. I don’t think
it is reasonable for us to limit our CMake version to the lowest common
denominator of all Linux distributions. I really think the Linux developers
should just do what I do on OS X and build it from source. Building CMake is
really simple and fast.
> 
> This is kinda a bit of a sore point for me because it turns out that our
CMake goop for cross-compiling is pretty nasty, and there are features in CMake
3.x that make it a lot better. Unfortunately using the new features while
supporting CMake 2.8.x would only make our goop goopier.
How does raising from 2.8.9 to 2.8.12.1 helps? It won’t bring the 3.x features
that you’d like to have.

As I understood it, bumping the version to 2.8.12.1 is motivated by a bug
related to "MSVC + Ninja” (http://www.cmake.org/Bug/view.php?id=14492 )

If this is indeed a bug in CMake that affects one very specific
platform/configuration, I don’t see this alone as a justification to raise the
requirement for all the platform.
It is up to the user of the platform not to use a CMake version that is buggy
for their platform/configuration.

Now you may have other good reasons to bump the CMake requirement but it is not
clear from this thread.

— 
Mehdi

> On Feb 24, 2015, at 11:13 AM, Mehdi Amini <mehdi.amini at apple.com>
wrote:
> 
>> 
>> On Feb 24, 2015, at 9:33 AM, Chris Bieneman <beanz at apple.com>
wrote:
>> 
>>> 
>>> On Feb 24, 2015, at 8:45 AM, Tobias Grosser <tobias at
grosser.es> wrote:
>>> 
>>> On 09.02.2015 20:12, Chris Bieneman wrote:
>>>> It came up on another thread that our current minimum required
CMake version 2.8.8, has some bugs that cause issues when building with MSVC +
Ninja, and one potential solution was to raise the minimum required version of
CMake.
>>>> 
>>>> CMake 3.0 is now 6 months old and CMake 3.1 has been released.
I would like to propose moving our minimum required CMake version to 3.0.
>>>> 
>>>> I’ve attached patches to enforce the change in case anyone
wants to test it out.
>>>> 
>>>> Thoughts/comments/concerns/objections?
>>> 
>>> Hi Chris,
>>> 
>>> this update broke my cmake LLVM+Polly buildbot (to my knowledge
most other bots use autoconf). I reverted this temporarily to avoid the buildbot
noise (this comes a little late, as I was traveling the last days).
>> 
>> Actually at this point I think most bots are on CMake. The green dragon
bots are all CMake, Galina and Takumi’s bots are at least partially on CMake.
>> 
>>> 
>>> The buildbot is based on the latest debian stable (wheezy), which
comes with cmake 2.8.9. Is 2.8.9 enough to fix the bug?
>> 
>> No. The bug requires 2.8.12.1. I really wanted 3.0, but Chandler
requested 2.8.12.2 because it was the version in the latest Ubuntu LTS.
>> 
>> I’m going to put on my “unpopular opinion” hat for a second. I don’t
think it is reasonable for us to limit our CMake version to the lowest common
denominator of all Linux distributions. I really think the Linux developers
should just do what I do on OS X and build it from source. Building CMake is
really simple and fast.
>> 
>> This is kinda a bit of a sore point for me because it turns out that
our CMake goop for cross-compiling is pretty nasty, and there are features in
CMake 3.x that make it a lot better. Unfortunately using the new features while
supporting CMake 2.8.x would only make our goop goopier.
> 
> How does raising from 2.8.9 to 2.8.12.1 helps? It won’t bring the 3.x
features that you’d like to have.
> 
> As I understood it, bumping the version to 2.8.12.1 is motivated by a bug
related to "MSVC + Ninja” (http://www.cmake.org/Bug/view.php?id=14492
<http://www.cmake.org/Bug/view.php?id=14492> )
Raising CMake 2.8.12.x allows us to remove a bunch of crufty hacks to support
older versions, and it gets some critical bug fixes for Visual Studio and Xcode
generators (like support for Xcode 5). There are a lot of features in 2.8.10,
2.8.11 and 2.8.12 that would be nice to have too.
> 
> If this is indeed a bug in CMake that affects one very specific
platform/configuration, I don’t see this alone as a justification to raise the
requirement for all the platform.
> It is up to the user of the platform not to use a CMake version that is
buggy for their platform/configuration.
I actually think we should establish a policy for updating the minimum required
version of CMake similar to how we update minimum required compiler versions.
That will allow us to take advantage of the fact that the CMake team makes rapid
progress without carrying a lot of baggage for maintaining compatibility of
older versions.

For context. CMake 2.8.9 was released in 8/2012, 2.8.12 was released 11/2013,
3.0 was released 6/2014, and 3.1 was released 12/2014.

I suspect that supporting 2 releases back (like we do for VS) probably isn’t
sufficient because that’s only about 6 months, but I think supporting back to
2012 is a bit much for CMake because the project is moving really quickly.

-Chris
> 
> Now you may have other good reasons to bump the CMake requirement but it is
not clear from this thread.
> 
> — 
> Mehdi
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