[llvm-dev] RFC: Updating to CMake 3.15.0

Tue Nov 5 08:42:13 PST 2019

I realize that this seems like a dumb question, and it’s only a matter of
perception, but, what’s the difference between a bootstrap script and a
copy-paste-able command in the documentation?  Would that be sufficient to
reduce the barrier to entry?

On Mon, Nov 4, 2019 at 9:39 AM David Blaikie via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
>
> On Mon, Nov 4, 2019 at 9:34 AM Chris Bieneman via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> I'm not sure what benefit that would provide. For most developers they
>> already have configured build directories
>>
>
> While I agree adding a bootstrap script is probably not worth the cost -
> an/the important benefit wouldn't be to existing developers, but to making
> the barrier of entry lower to encourage new contributors, I think.
>
>
>> and if their CMake is too old they are going to do a `git pull` and all
>> of a sudden their build fails to configure. Then they go fetch a new CMake.
>> Not sure a bootstrap script really helps with that. Especially since the
>> CMake git repository contains one, and many people might prefer to grab a
>> binary distribution rather than build their own.
>>
>> -Chris
>>
>> On Nov 4, 2019, at 9:29 AM, Stephen Neuendorffer <
>> stephen.neuendorffer at gmail.com> wrote:
>>
>> Maybe a bootstrap.sh?  I understand that it can get a little tricky, but
>> even if it only worked 95% of the time it might be enough to lower the
>> barrier to entry.
>>
>> Steve
>>
>> On Mon, Nov 4, 2019 at 9:16 AM Chris Bieneman <chris.bieneman at me.com>
>> wrote:
>>
>>> CMake doesn’t have the ability to reliably re-invoke itself in a way
>>> that would make that workflow reasonable. To do it would require a meta
>>> build system for our meta build system, and that is the road to madness.
>>>
>>> -Chris
>>>
>>> On Nov 4, 2019, at 8:59 AM, Stephen Neuendorffer via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>> 
>>>
>>> Since it's 'so easy', I wonder if it would make people's lives easier to
>>> add a bootstrap of cmake to the out of the box build flow.
>>> Maybe: "You're system Cmake is too old for us.  Downloading and building
>>> a cmake 1.15.1 locally for you...."
>>>
>>> Steve
>>>
>>> On Mon, Nov 4, 2019 at 7:20 AM James Y Knight via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> On Sun, Nov 3, 2019 at 7:20 PM Neil Nelson via llvm-dev <
>>>> llvm-dev at lists.llvm.org> wrote:
>>>>
>>>>> Glad we are getting some reasonable justifications for CMake 3.15.0.
>>>>> There are two points we may be missing.
>>>>>
>>>>> Is our plan to just keep updating to the most recent CMake version or
>>>>> will our objectives be reached with this version? If we gain what we need
>>>>> with this version then after a while we will have the Ubuntu LTS aligned.
>>>>>
>>>>> For my current purposes, LLVM can get wild without much worry here. I
>>>>> just clone a VM and run what is useful and then delete it. A bit like use
>>>>> once and throw away. This is not for production purposes but for getting a
>>>>> better view of software structure that LLVM can provide.
>>>>>
>>>>> When I was managing IT and the servers for a small company that needed
>>>>> to be live 24/7 we used the latest Ubuntu LTS version because we needed
>>>>> rock-solid performance as best we could get. The software in the LTS
>>>>> version is tested and used by a large user base with necessary updates and
>>>>> so we expected to have high reliability.
>>>>>
>>>>> Those saying how easy it was to obtain the latest CMake have
>>>>> apparently not been faced with the absolute need for solid up-time.
>>>>> Installing hack-me-now, buggy, bleeding-edge software was severely
>>>>> discouraged. But in the LLVM environment, I can see where that is not a
>>>>> strong necessity.
>>>>>
>>>>> But at the same time, does LLVM strive to be the backbone of 24/7
>>>>> software? Or is it more of a cool thing with some interesting code analysis
>>>>> properties? I suspect its nature is a bit wild, bleeding edge. And that's
>>>>> OK.
>>>>>
>>>> I'm not really sure what your worry is here -- if you're downloading
>>>> and building a development version of LLVM onto this particular production
>>>> machine, why is it problematic to also download a newer release version of
>>>> CMake to build it with?
>>>>
>>>> Maybe you're worried that you'd have to install the new cmake into
>>>> /usr/local/bin? If that's the worry, I'll note that you are not required to
>>>> install cmake into /usr/local/bin/ in order to use it to build LLVM, and
>>>> I'd recommend not doing so. You can actually invoke the cmake binary
>>>> directly from its build/download directory -- no "make install" required at
>>>> all. Used that way, it doesn't affect anything else on your system -- if
>>>> you like, the new cmake can be used ONLY for building LLVM, and affect
>>>> literally nothing else other than a tiny amount of disk-space.
>>>>
>>>> Another important point here is that the version of cmake you use to
>>>> build llvm doesn't impact users of the llvm libraries or binaries that were
>>>> built with the new cmake. (I'd contrast that with llvm requiring a newer
>>>> version of a shared library, which _does_ have runtime impact, and thus is
>>>> of potentially larger concern.)
>>>>
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>>>>
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-- 
Saleem Abdulrasool
compnerd (at) compnerd (dot) org
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