[LLVMdev] [RFC] Raise minimum required CMake version to 3.0

[Chris Bieneman]

(adding chandler to the To line)

> On Mar 10, 2015, at 12:29 PM, Tobias Grosser <tobias at grosser.es> wrote:
> 
> Chandler previously asked to ensure we stay with a cmake version that is available in the Ubuntu packages. If you want to drop this requirement, you probably want to cross-check with him.

Chandler, do you have any thoughts based on the context in this thread? Please take as long as you need to digest it all, there is no imminent rush here.

> 
> I personally also believe being a little bit more conservative here would be nice, if possible, as it keeps the barrier of entry to LLVM lower and also makes moving away from autoconf easier.

Actually, the point I was trying to make earlier is that moving away from autoconf is HARDER on older versions of CMake. Yes everyone has make and can run configure, but CMake 2.8.x lacks features that would make it easier to support the remaining bits of functionality from the autoconf build system that the CMake one is lacking.

Also, as I’ve pointed out before, building CMake from source is really easy, even on a system that doesn’t have an existing version of CMake. So while I understand (and am willing to accept) that installing from packages is easy and convenient, I’m not sure we should make it a requirement.

Either way, at the moment I have no patches to land which use new features of CMake, so I’m not actually pushing to raise the minimum version today. As I see it, this conversation is more about establishing a policy, and determining what qualifies as a justification to update CMake versions.

Personally I would prefer to say we support all stable CMake releases going back 12 months. That would allow us to take advantage of new features 12 months after they are introduced, and it keeps us moving forward.

Alternatively if we adopt an approach of raising to the minimum version supported by Ubuntu LTS and Debian Stable, we’ll be stuck in a cycle where every two years we get to update to a version we have no influence over.

-Chris
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