[CMake] [PATCH] FindBoost does not detect absence of header file

[rleigh at codelibre.net]

On 2016-04-12 11:22, Joachim Wuttke wrote:
> FindBoost does not detect absence of header files.
> 
> To be specific: Run the following under cmake version 3.5.1:
> 
> set(Boost_NO_BOOST_CMAKE ON) # prevent shortcut
> set(Boost_USE_STATIC_LIBS OFF)
> set(Boost_USE_MULTITHREADED ON)
> set(Boost_USE_STATIC_RUNTIME OFF)
> add_definitions(-DBOOST_ALL_DYN_LINK) # line is needed for MSVC
> #add_definitions(-DBOOST_LIB_DIAGNOSTIC) # shows during compilation
> auto-linked libraries
> if(WIN32)
>     set(boost_libraries_required date_time chrono program_options zlib
> bzip2 iostreams system filesystem regex thread)
> else()
>     set(boost_libraries_required date_time chrono program_options
> iostreams system filesystem regex thread)
> endif()
> find_package(Boost 1.48.0 COMPONENTS ${boost_libraries_required} 
> REQUIRED)
> message(STATUS "--> Boost_INCLUDE_DIRS: ${Boost_INCLUDE_DIRS}")
> message(STATUS "    Boost_LIBRARY_DIRS: ${Boost_LIBRARY_DIRS}")
> message(STATUS "    Boost_LIBRARIES: ${Boost_LIBRARIES}")
> 
> It will pass, even if files like /usr/include/boost/date_time.hpp &c 
> are removed
> from the system.

Attached is a patch to add this extra checking.

For each library component, there is a corresponding header which has 
been present in all versions of boost to date which provide the library; 
the list used to validate this is also attached.  I have also validated 
that each component works with find_package for Boost 1.58 and 1.60.

If your system contains both the libraries and headers, then FindBoost 
will behave exactly as before.  But if you have the libraries without 
the headers, FindBoost will now fail, rather than passing and then 
having the build subsequently fail when it tries to use the nonexistent 
headers.  So it's essentially adding an additional header check per 
component, which will identify situations where the user has an 
incomplete Boost installation e.g. no all the -dev packages are 
installed.

I can merge this into next for testing, but if anyone wanted to have an 
initial play with it to verify that it's still functional and that the 
approach is sound, I can wait off for now.


Regards,
Roger
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