[cmake-developers] Modern cross-platform buildsystem design requirements

[Stephen Kelly]

Hi,

I saw the addition of the VS_WINRT_COMPONENT property. This seems to be an 
attribute to mark an executable specially so that it is built with 
appropriate flags for the WinRT platform.

This reminds me of this thread:

 http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/9728
 Building executables as libraries
 (2014-03-21)

and I wonder again if a generic solution would be possible to design. 

I wonder what a cmake-based buildsystem would look like for a collection of 
executables/targets which should be built for multiple of these 'modern, 
extra attribute-requiring' platforms. 

Until a few years ago,

 add_library(foo foo.cpp)
 add_executable(myexe main.cpp)
 target_link_libraries(myexe foo)

was all that was needed for what we then called 'cross-platform' - it is a 
sufficient description to generate buildsystems to generate a working 
library and executable on first-class targets Windows/Linux/Mac and also 
cross-compiling, given an appropriate toolchain file.

Today, I think 'cross-platform' includes a few mobile platforms as first-
class targets, and cross-compiling is part of what cross-platform means. So, 
I wonder what a cross-platform buildsystem necessarily looks like today, and 
whether it can be done better/abstracted with more first class features.

I guess in addition to the above, there would need to be something like a 
wrapper macro around add_executable to set the appropriate target 
properties, and possibly use a platform-specific condition for whether to 
actually create an executable or a PIC shared library (as described in the 
above thread). Is there any known real-world project aiming to build for 
those varieties of platforms so we can see what abstraction is needed?

According to 

 http://www.cmake.org/Wiki/CMake_Cross_Compiling#FAQ.2FPotential_Problems

"If you build software for PS3, you build software for two architectures, 
for the PowerPC and for the cells."

That information seems to come from:

 http://www.cmake.org/pipermail/cmake/2008-January/018937.html

I was reminded of the above by 

 http://thread.gmane.org/gmane.comp.programming.tools.cmake.user/50389

I don't know how common it is to use cmake in those industries/environments, 
but if multiple toolchains are needed, I'm reminded of the previous proposal 
for multiple toolchain use.

 http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/7272

Partly that discussion was aborted because we already had the large topic of 
designing and implementing usage-requirements to deal with. As that is now 
complete as designed, it might be worthwhile to re-consider and 
discuss/design how multiple toolchains could be used at once, whether that 
would require or benefit from a new language for cmake (another orthogoal 
known possible future-direction for cmake) etc.

[
The manual at 

 Help/manual/cmake-toolchains.7.rst

contains several sample toolchain files for Unix. It would be good to have 
some sample toolchain files using the new WinRT stuff, setting the toolset 
and CMAKE_GENERATOR_PLATFORM to see how that all fits together now with 
VisualStudio.
]

Thanks,

Steve.