Re: [Boost-cmake] multiple installed versions, FindBoost.cmake, exported targets, etc.

Subject: Re: [Boost-cmake] multiple installed versions, FindBoost.cmake, exported targets, etc.
From: troy d. straszheim (troy_at_[hidden])
Date: 2009-11-01 22:17:55

Correction to the below:  replace /usr/ (as in /usr/share) with 
${CMAKE_INSTALL_PREFIX}/

Sorry for any confusion.

-t

troy d. straszheim wrote:
> Here's what I've got.  There are several options controlling how things 
> are built and installed, here are short descriptions:
> 
> INSTALL_VERSIONED:  mangle boost version into installed dirnames
> 
> So with INSTALL_VERSIONED off:
> 
> % cmake .. -DCMAKE_INSTALL_PREFIX=/tmp/local
> 
> install layout:
> 
> Headers:
> /tmp/local/include//boost/mpi.hpp
> /tmp/local/include//boost/noncopyable.hpp
> 
> Installed exported targets:
> /tmp/local/lib/boost/cmake/Boost.cmake
> /tmp/local/lib/boost/cmake/Boost-release.cmake
> 
> Libs:
> /tmp/local/lib/libboost_thread-mt.a
> /tmp/local/lib/libboost_thread-mt.so.1.41.0
> /tmp/local/lib/libboost_thread-mt.so
> 
> Standard CMake infrastructure:
> /usr/share/boost/cmake/BoostConfigVersion.cmake
> /usr/share/boost/cmake/BoostConfig.cmake
> 
> Version-specific cmake infrastructure:
> /usr/share/boost/cmake/Boost-1.41.0.cmake
> 
> So here you have a 'main' unversioned install .  It is possible to also 
> have versioned installs alongside it, but you may have only one 
> unversioned install.
> 
> 
> 
> You may have many installs via INSTALL_VERSIONED=ON:
> 
> cmake .. -DINSTALL_VERSIONED=ON
>          -DCMAKE_INSTALL_PREFIX=/tmp/local
> 
> Install layout:
> 
> Headers:
> /tmp/local/include/boost-1.41.0/boost/mpi.hpp
> /tmp/local/include/boost-1.41.0/boost/noncopyable.hpp
> 
> Installed exported targets:
> /tmp/local/lib/boost-1.41.0/Boost.cmake
> /tmp/local/lib/boost-1.41.0/Boost-release.cmake
> 
> Libs:
> /tmp/local/lib/boost-1.41.0/libboost_thread-mt.a
> /tmp/local/lib/boost-1.41.0/libboost_thread-mt.so.1.41.0
> /tmp/local/lib/boost-1.41.0/libboost_thread-mt.so
> 
> Standard CMake infrastructure:
> /usr/share/boost/cmake/BoostConfigVersion.cmake
> /usr/share/boost/cmake/BoostConfig.cmake
> 
> Version-specific cmake infrastructure:
> /usr/share/boost/cmake/Boost-1.41.0.cmake
> 
> 
> So the only files that conflict are BoostConfig.cmake and 
> BoostConfigVersion.cmake in /usr/share/boost/cmake;  but they don't 
> really conflict, because they are version agnostic.
> 
> How it works:  When you do
> 
>   find_package(Boost 1.41.0 COMPONENTS thread NO_MODULE)
> 
> First /usr/share/boost/cmake/BoostConfigVersion.cmake is called.
> it looks for Boost-${PACKAGE_FIND_VERSION} alongside it, and if it is 
> there, it sets PACKAGE_VERSION to ${PACKAGE_FIND_VERSION} and so forth. 
>  If it doesn't find the exact version it looks for the newest version, 
> and sets PACKAGE_VERSION to that, etc.
> 
> Then /usr/share/boost/cmake/BoostConfig.cmake is run as usual;  it 
> simply does:
> 
>   get_filename_component(CWD ${CMAKE_CURRENT_LIST_FILE} PATH)
>   include("${CWD}/Boost-${Boost_VERSION}.cmake")
> 
> e.g. it includes /usr/share/boost/cmake/Boost-1.41.0.cmake.
> This file was generated by Boost.CMake, so it knows all about the 
> install, most importantly where the installed exported targets file is, 
> e.g. /tmp/local/lib/boost-1.41.0/Boost.cmake.  It then sets up 
> ${Boost_LIBRARIES} and all that good stuff using the imported targets.
> 
> So the following works fine, regardless of how many versions are 
> installed, with or without one of them installed 'unversioned', or how 
> strangely they are laid out:
> 
> set(Boost_USE_MULTITHREADED ON)
> 
> find_package(Boost
>   1.41.0
>   COMPONENTS thread
>   NO_MODULE
>   )
> 
> include_directories(${Boost_INCLUDE_DIR})
> 
> add_executable(main main.cpp)
> 
> target_link_libraries(main ${Boost_LIBRARIES})
> 
> Do I pass a sanity-check?  It has become hard to tell.  I think I'm 
> ready to request that Modules/FindBoost.cmake try Config mode first, so 
> that end users can omit the NO_MODULE in the find_package above when 
> cmake 2.8 comes out.
> 
> -t
> 
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