boost configured with -DBOOST_INCLUDE_LIBRARIES=headers does not install headers

[tfry-git]

I'm trying to install only the boost headers using the cmake build system. My impression was that this could be achieved by configuring with cmake -DBOOST_INCLUDE_LIBRARIES=headers. However, this seems to result in installing only the cmake files, but not the headers.

In direct comparison, using b2, bootstrap --with-libraries=headers works as expected.

In detail:

wget https://github.com/boostorg/boost/releases/download/boost-1.92.0/boost-1.92.0-cmake.tar.xz
tar xf boost-1.92.0-cmake.tar.xz
cd boost-1.92.0
cmake -DBOOST_INCLUDE_LIBRARIES=headers .
make install DESTDIR=/tmp

Full output of make install:

Install the project...
-- Install configuration: "Release"
-- Up-to-date: /tmp/usr/local/include
-- Up-to-date: /tmp/usr/local/include/boost
-- Up-to-date: /tmp/usr/local/include/boost/headers
-- Up-to-date: /tmp/usr/local/include/boost/headers/.gitkeep
-- Installing: /tmp/usr/local/lib/cmake/boost_headers-1.92.0/boost_headers-targets.cmake
-- Installing: /tmp/usr/local/lib/cmake/boost_headers-1.92.0/boost_headers-config.cmake
-- Installing: /tmp/usr/local/lib/cmake/boost_headers-1.92.0/boost_headers-config-version.cmake
-- Up-to-date: /tmp/usr/local/lib/cmake/Boost-1.92.0/BoostConfig.cmake
-- Installing: /tmp/usr/local/lib/cmake/Boost-1.92.0/BoostConfigVersion.cmake

[tfry-git]

Addendum: using cmake 4.4.2

[pdimov]

No, it's not possible to install only the headers with CMake. The headers "library" is only there for compatibility, it doesn't contain anything. The headers are part of the appropriate library subprojects, and can't be installed separately.

b2 can install just the headers for historical reasons (in a "normal" Boost release, the headers aren't part of the individual libraries, but are moved into a single boost/ directory as part of the release process.)

You can control the directories where the various artifacts are installed using the standard CMake variables, though.

[tfry-git]

The headers "library" is only there for compatibility

Of course this is more of a cosmetic issue, and maybe a feature request, but: Many consuming projects need only the boost headers, and you provide cmake support to find/use only the headers. It would rather make sense to me that - if you allow to customize the boost build at all - building/installing only the headers should be among the supported options.

[nigels-com]

My thought is that it's generally expected that a header-only CMake library would install the headers.
It seems reasonable for boost to do the same, ideally.
I'll take a look, if I get a chance.