Re: Using Boost.Test header-only from CMake

From: Peter Dimov (pdimov_at_[hidden])
Date: 2021-06-07 23:58:24

Raffi Enficiaud wrote:
> I have not looked at the recent developments for CMake in Boost. If the
> CMakeLists.txt I developed (under build/) is still there, it contained 2
> targets: one for static and one for shared. Those were having different and
> explicit names.

I decided to not do this and instead use the "normal" CMake way of relying
on BUILD_SHARED_LIBS.

It causes problems in the more complicated cases where a compiled Boost::X
links to header-only Boost::Y which links to a compiled Boost::Z. Client code
can choose to link explicitly to Boost::static_X, and if X used Z directly, it could
link to Boost::static_Z, but it doesn't. And requiring all header-only libraries
to also provide triplicate targets so that static/shared-ness can be propagated
correctly is (I think) infeasible. So X links to Boost::Y, and Y has to choose
whether to link to the static or shared Z, but it doesn't know how.

(b2 does this "right" by having static/shared as a build feature, and
propagating it automatically. No need to split your targets by hand.)

Swimming upstream is sometimes justified when it results in something
objectively better than the accepted CMake way, but I don't believe that's
the case here, so BUILD_SHARED_LIBS will have to do. (Similarly, I tried to do
something b2-like with the tests, but at the end reverting to the way CMake
wants to do things proved better.)

Getting back to Boost.Test, I've duplicated the targets with an included_ prefix:

https://github.com/boostorg/test/commit/bce2d24c8b32f47f0403766fe4fee3e2e93af0a0