Re: Adding CMakeLists.txt files

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2021-05-28 15:08:37

On 5/28/21 5:20 PM, Adam Wulkiewicz via Boost wrote:
> 
> Should optional dependencies be listed?
> I'm asking because we provide optional files for adapting e.g. Polygon 
> models to use them with Geometry. The same is or will be true for 
> Variant, Variant2 and Any. R-tree support for serialization is optional 
> as well and enabled with #ifdef. The extensions are optional and exists 
> only in develop branch. Etc.

Peter already answered this, but I can add that you could conditionally 
add optional dependencies in CMake by checking the environment and/or 
user configuration options and call target_link_libraries only when 
needed. You can see an example in Boost.Filesystem:

https://github.com/boostorg/filesystem/blob/develop/CMakeLists.txt

> Are these dependencies only for includes or also for tests, examples and 
> sources from documentation?

The CMakeLists.txt that is in the root library directory is used when 
the library is built or consumed by users. So, the PRIVATE dependencies 
are those required to build the library (but not to consume it) and 
PUBLIC - those required to consume it. IOW, the dependencies from source 
files normally go in PRIVATE section and from headers - in PUBLIC. Tests 
and examples are not described there.

For tests and examples there may be separate CMakeLists.txt (in test/ 
and example/) that would describe their respective dependencies, 
including on the library itself. Those CMakeLists.txt are not required 
to build or consume Boost, so currently are not mandatory.