Re: [boost] Proposal for moving Boost to CMake

Subject: Re: [boost] Proposal for moving Boost to CMake
From: P F (pfultz2_at_[hidden])
Date: 2017-06-20 06:06:45

> On Jun 19, 2017, at 9:24 PM, Peter Dimov via Boost <boost_at_[hidden]> wrote:
> 
> Louis Dionne wrote:
>> So, normally, for a project based on CMake, these XYZConfig.cmake files can be generated automatically by using `install(EXPORT ...)`. The resulting file looks like this (for Hana):
>> 
>> https://gist.github.com/ldionne/df7b6888752097e25bfc2333f6d897ca#file-what-gets-generated-for-hana-cmake
>> 
>> Basically, we'd want to replicate the functionality provided by this module without necessarily all the boilerplate (since that's generated automatically). Here's a minimal file for Hana (a header only library):
>> 
>> https://gist.github.com/ldionne/df7b6888752097e25bfc2333f6d897ca#file-minimal-handwritten-config-header-only-cmake
>> 
>> And here's a minimal XYZConfig.cmake file for a library with compiled sources (I added source files to Hana and turned it into a static library to check this):
>> 
>> https://gist.github.com/ldionne/df7b6888752097e25bfc2333f6d897ca#file-minimal-handwritten-config-static-cmake
> 
> Thanks, this gives me an idea what you were proposing. One thing I notice is that you don't enumerate any dependencies. This would work fine in the case where all our header-only libraries are installed into the same include/ as one -I would be as good as any other, I suppose.

He didn’t enumerate the dependencies because in this example there wasn’t any dependencies. If there are dependencies, it would look something like this:

include(CMakeFindDependencyMacro)
# Bring in the boost::fusion imported target
find_dependency(boost_fusion)
# Bring in the boost::config imported target
find_dependency(boost_config) 

# Snip the computing imported prefix ...

set_target_properties(boost::hana PROPERTIES
  INTERFACE_COMPILE_FEATURES "cxx_std_14"
  INTERFACE_INCLUDE_DIRECTORIES "${_IMPORT_PREFIX}/include"
  INTERFACE_LINK_LIBRARIES "boost::fusion;boost::config"
  IMPORTED_LINK_INTERFACE_LANGUAGES "CXX"
  IMPORTED_LOCATION "${_IMPORT_PREFIX}/lib/libhana.a"
  # Whatever else you need
)

> 
>> Then, each Boost library would simply provide a file like this and install it to the appropriate location when the library is installed.
> 
> So, if I understand correctly, you're saying that after `b2 install` in addition to the headers in $prefix/include and the built libraries in $prefix/lib, we should also copy these boost_*-config.cmake files (along with the corresponding -version files maybe?) into $prefix/lib/cmake?

Actually the files will go into $prefix/lib/cmake/boost_pumpkin

> 
> Which would then presumably enable find_package(boost_pumpkin)? 

Yes.