[cmake-developers] Using CMake as a library from Python

[Charles Huet]

Yes, this is POC-only.

I felt too lazy to make an argparse object and properly perform these tasks.
Obviously, the generator and source dir should be arguments.
The build dir should be the execution dir of the script, to mimic CMake
behavior.

This should not be difficult, but as I said I wanted first to get this
disussion started.

Le lun. 4 janv. 2016 à 11:54, Tamás Kenéz <tamas.kenez at gmail.com> a écrit :

> Charles,
>
> I'd like to comment on a minor issue:
>
> CMakeLists.txt files don't specify user-specific data like source and
> build dirs (for a reason) yet your POC listfile contains this line:
>
>     cmake.init("Ninja", "/media/dev/src/cmaketest",
> "/media/dev/build/cmaketest")
>
> which sets the source and build directories. Is this some temporary
> solution for the POC only?
>
> Tamas
>
> On Mon, Jan 4, 2016 at 8:41 AM, Charles Huet <charles.huet at gmail.com>
> wrote:
>
>> Hi,
>>
>> Because of the above, I worry that you are basing your work on an old
>>> version of CMake. As of April 2015 cmState is used as the interface to
>>> the
>>> cache.
>>
>>
>> Yeah, that is sadly right. I wanted to rebase on master before
>> publishing, thinking it should not be too hard, and I have lots to re-do,
>> mostly understand how things are done now.
>>
>> I did something similar some years ago with QML instead of python, so it
>>> sounds interesting to me.
>>
>>
>> I'm trying to be as declarative as possible, because really like how
>> readable simple QML programs are, and I think it would be perfect for a
>> buildsystem.
>>
>> My guess is that you are using python to instantiate a cmAddLibraryCommand
>>> and then executing it.
>>
>>
>> Actually, I'm directly using the cmMakefile, because I did not want to
>> wrap all the commands, and it seemed backwards to me to wrap them.
>>
>> Even much of cmMakefile shouldn't be used by a new language. Instead
>>> certain
>>> parts of cmMakefile should be extracted as other classes
>>> (cmVariableExpander
>>> which should have the ExpandVariablesInString and ConfigureString stuff,
>>> cmMessenger for the IssueMessage stuff, some other class for the
>>> CompileFeature stuff etc). Then cmMakefile would be just about executing
>>> and
>>> scoping the CMake language. A new language would not need that, but would
>>> use the refactored extracted classes.
>>
>>
>> Ah, this is very interesting, thanks.
>>
>>
>> Having said all that, Brad favors Lua I believe, and he favors a different
>>> approach (which no one is working on as far as I know) to adding a new
>>> language. So wait to hear from him to know whether it is something that
>>> would be upstreamable.
>>
>>
>> Have any details on the approach in question ? SWIG would allow for Lua
>> bindings as easily, but I don't think having multiple languages would be a
>> good idea.
>> I went with Python because I'm familiar with it and have already written
>> bindings for it with SWIG. Also, buildbot is written in python and it could
>> provide a really interesting integration I think.
>>
>> I would guide/support you in refactoring cmake as needed. The refactoring
>>> part would definitely be upstreamable. I would very much like to see a
>>> proof
>>> of concept alternative language even if that wasn't upstreamed. It would
>>> prove that another language is possible, and that's one of the steps to
>>> replacing the current cmake language I think.
>>
>>
>> I will need to work on it to make it work again with master, but I'll try
>> and do this soon.
>>
>> Here is what my test POC looked like for generating a simple shared
>> library:
>>
>> #!/usr/bin/env python
>>> # -*- coding: utf-8 -*-
>>> import cmake
>>> cmake.init("Ninja", "/media/dev/src/cmaketest",
>>> "/media/dev/build/cmaketest")
>>> myProject = cmake.Project("MyTestProject")
>>> myProject.targets = [ cmake.SharedLibrary("testLibrary", ["lib.cxx"]) ]
>>> cmake.generate()
>>
>>
>> Thanks a lot for your comments, I'm happy to see this was not just a dumb
>> idea, and that others have thought about it.
>>
>> I'll update with the github as soon as I get it working.
>>
>> Best
>>
>>
>> Le lun. 4 janv. 2016 à 01:16, Stephen Kelly <steveire at gmail.com> a
>> écrit :
>>
>>> Charles Huet wrote:
>>>
>>> > * cmCacheManager::AddCacheEntry was made public, as cmake::Configure
>>> > cannot be used from python (it check for the existence of a
>>> CMakeLists.txt
>>> > file, which does not exist in this scenario) and the cache variables it
>>> > sets seem to be necessary.
>>>
>>> Because of the above, I worry that you are basing your work on an old
>>> version of CMake. As of April 2015 cmState is used as the interface to
>>> the
>>> cache.
>>>
>>>  https://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=a6b1ad13
>>>
>>> Also note that the C++ interfaces in CMake are not stable. In the last
>>> year
>>> they have been changed utterly and that will continue to happen without
>>> notice. I'm sure you know this, but I thought I'd say it anyway.
>>>
>>> > I will try to make a layer of abstraction on top of the python bindings
>>> > before publishing this work on github, in order to show the syntactic
>>> > sugar python can provide, but I will publish this before if anybody is
>>> > interested in working on this.
>>>
>>> I would be interested in seeing it.
>>>
>>> > Now, does anyone beside me think this is a good idea ?
>>>
>>> I did something similar some years ago with QML instead of python, so it
>>> sounds interesting to me.
>>>
>>> In fact, one of the reasons for introducing cmState and doing all the
>>> refactoring I did in cmake was to make it possible to cleanly replace the
>>> language, some day.
>>>
>>> My guess is that you are using python to instantiate a
>>> cmAddLibraryCommand
>>> and then executing it. I think a better approach would be to leave all
>>> the
>>> cm*Command classes behind as they carry a lot of backward compatibility
>>> baggage and policies which a new language shouldn't be burdened with.
>>>
>>> Even much of cmMakefile shouldn't be used by a new language. Instead
>>> certain
>>> parts of cmMakefile should be extracted as other classes
>>> (cmVariableExpander
>>> which should have the ExpandVariablesInString and ConfigureString stuff,
>>> cmMessenger for the IssueMessage stuff, some other class for the
>>> CompileFeature stuff etc). Then cmMakefile would be just about executing
>>> and
>>> scoping the CMake language. A new language would not need that, but would
>>> use the refactored extracted classes.
>>>
>>> So, you would implement new cmPython*Command or whatever which operate on
>>> those classes and cmState. cmState is designed to be a language-agnostic
>>> store of data, like a database of buildsystem state.
>>>
>>> As I said though, this would require further refactoring of the cmake
>>> code.
>>> I can provide guidance on how to do that if you are interested in
>>> pursuing
>>> that route. It would take some months I think, but be very valuable for
>>> many
>>> reasons and long-term cmake features. Another example of the kind of
>>> refactoring I mean is putting target state in cmState and making it
>>> accessible through cmState::Target, similar to how cmState::Directory
>>> currently works.
>>>
>>> Having said all that, Brad favors Lua I believe, and he favors a
>>> different
>>> approach (which no one is working on as far as I know) to adding a new
>>> language. So wait to hear from him to know whether it is something that
>>> would be upstreamable.
>>>
>>> I would prefer an approach similar to what I described above, which is
>>> close
>>> to what you are doing, so as a proof of concept I would like to see your
>>> work.
>>>
>>> I would guide/support you in refactoring cmake as needed. The refactoring
>>> part would definitely be upstreamable. I would very much like to see a
>>> proof
>>> of concept alternative language even if that wasn't upstreamed. It would
>>> prove that another language is possible, and that's one of the steps to
>>> replacing the current cmake language I think.
>>>
>>> Thanks,
>>>
>>> Steve.
>>>
>>>
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>>
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>>
>> Powered by www.kitware.com
>>
>> Please keep messages on-topic and check the CMake FAQ at:
>> http://www.cmake.org/Wiki/CMake_FAQ
>>
>> Kitware offers various services to support the CMake community. For more
>> information on each offering, please visit:
>>
>> CMake Support: http://cmake.org/cmake/help/support.html
>> CMake Consulting: http://cmake.org/cmake/help/consulting.html
>> CMake Training Courses: http://cmake.org/cmake/help/training.html
>>
>> Visit other Kitware open-source projects at
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