CMake and Boost

From: Robert Ramey (ramey_at_[hidden])
Date: 2024-06-11 05:21:11

I'm trying to figure out how to switch to CMake to build and test my 
libraries.  I have some experience with this as I've made such files on 
sort of an experimental/prototype basis.  However it's been some time 
since I messed with this so a forgot a lot. Now I'm getting serious so I 
have some questions.  I've looked over the official CMake documentation. 
  It seems complete but some stuff is not well explained.  I've spent 
some time studying https://github.com/boostorg/cmake at I'm beginning to 
see what I have to do.  Never-the-less, I still have a few questions:

1) The first lines show

mkdir __build
cd __build
cmake ..
cmake --build .

Does this presume that one starts from the library directory?
Does this syntax work for out of source tree builds?  That is, would the 
following work?

mkdir /temp/__build
cd /temp/__build
cmake ..
cmake --build .

(very confusing usage of leading __)

ahhhh - I see a problem.  I'm thinking of starting from within the 
directory of a particular library.  I'm presuming "modular boost".  Is 
this supported?

2) BOOST_INCLUDE_LIBRARY

I would like my CMakeLists.txt file to explicitly list the direct 
antecedent libraries (dependencies - bad word usage).  So I'd expect to 
see something like

add_directory(../filesystem)
add_directory(../regex)
...

So I could just
cd to .../libs/serialization
cmake --build

and have it build the antecedent if and only if required.

3) CMAKE_INSTALL_INCLUDEDIR

I would prefer not to "install" (copy) the include files but just use 
the ones from their original locations.

4) BUILD_TESTING

I would prefer to have my library source to look like:

... libs/serialization
   CMakeLists.txt
     // includes add_directory for subdirectorys build, test, example, 
profile and ...
     // includes add_directory for antecedent libraries like 
add_directory(../libs/filesystem)
   include // directory with include files for users of serialization 
library
   build(or src) // source files for library build
     CMakeLists.txt // to build library
   test
     CMakeLists.txt
   example
     CMakeLists.txt
   profile
     CMakeLists.txt

Maybe the add_directory would be conditioned on a CMAKE variable.

So if I invoke

CMake --build test_polymorphic_binary_archive

It would recursively (re)build everything necessary and nothing not 
necessary

If I didn't specify a list of targets, it would recursively (re)build 
everything that needs (re)building.

This seems totally reasonable and natural to me - it work like make - 
but better.  It would dovetail with efforts to "modularize" boost. 
Users would only have to download libraries they actually use - if 
that's what they want. I realized I've glossed over a couple of details, 
in particular recursive inclusion of header files and likely some other 
stuff.  I've also experimented with CMake enough to have a feeling that 
what I want to do is not possible.  And this is the short version of 
what I'd like to do.

Any thoughts on this?