Re: [boost] Proposal for moving Boost to CMake

Subject: Re: [boost] Proposal for moving Boost to CMake
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2017-06-22 09:36:13

On Thu, Jun 22, 2017 at 11:30 AM, P F via Boost <boost_at_[hidden]>
wrote:

>
> > On Jun 21, 2017, at 8:48 PM, Peter Dimov via Boost <
> boost_at_[hidden]> wrote:
> >
> > Louis Dionne wrote:
> >
> >> 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/df7b6888752097e25bfc2333f6d897
> ca#file-minimal-handwritten-config-static-cmake
> >
> > To get back to this... it ain't so easy. On Linux, where the default is
> --layout=system, you indeed can only have libhana.a and libhana.so (a link
> to libhana.so.1.65.0 or something like that).
> >
> > But on Windows, `b2 --build-type=complete --with-system
> toolset=msvc-14.1` gives you this:
> >
> > boost_system-vc141-mt-1_65.dll
> > boost_system-vc141-mt-1_65.lib
> > boost_system-vc141-mt-gd-1_65.dll
> > boost_system-vc141-mt-gd-1_65.lib
> > libboost_system-vc141-mt-1_65.lib
> > libboost_system-vc141-mt-gd-1_65.lib
> > libboost_system-vc141-mt-s-1_65.lib
> > libboost_system-vc141-mt-sgd-1_65.lib
> > libboost_system-vc141-s-1_65.lib
> > libboost_system-vc141-sgd-1_65.lib
> >
> > and of course compiling with a different toolset would give you the
> appropriate, different, names. You can have all of these installed
> simultaneously.
> >
> > So boost_system-config.cmake needs to be slightly more elaborate.
>
> Yes. For debug and release variants, I believe you can use the `$<CONFIG>`
> generator expression:
>
> set_target_properties(boost::system PROPERTIES
>   IMPORTED_IMPLIB "$<IF:$<CONFIG:release>,${_IMPORT_PREFIX}/lib/boost_
> system-vc141-mt-gd-1_65.lib,boost_system-vc141-mt-1_65.lib>"
>   IMPORTED_LOCATION "$<IF:$<CONFIG:release>,${_IMPORT_PREFIX}/lib/boost_
> system-vc141-mt-gd-1_65.dll,boost_system-vc141-mt-1_65.dll>"
> )
>

There are use cases when I want to get the release build of boost even
though my own build type is set to Debug. The build type in addition is
also completely customizable (see for example the MSVC CMake integration).
What should happen when my build type is RelWithDebInfo or MinSizeRel?
There should always be a way for users to bail out of the guessing game.

>
> Which will pick debug or release based on that. However, to choose between
> the other variants, we can probably use the `COMPONENTS` arguments in
> `find_package`. So the user can say `find_package(boost_system COMPONENTS
> static mt)`, or something like that. We also, probably want to make the
> components requests transitive as well:
>
> find_dependency(boost_system COMPONENTS ${${CMAKE_FIND_PACKAGE_NAM}_
> FIND_COMPONENTS})
>
>
>
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