Re: [boost] [cmake] Pull request announcement

Subject: Re: [boost] [cmake] Pull request announcement
From: James E. King III (jking_at_[hidden])
Date: 2018-09-19 13:05:43

On Mon, Sep 17, 2018 at 8:49 AM Peter Dimov via Boost <boost_at_[hidden]>
wrote:

> Alexander Grund wrote:
>
> > Besides that: Don't use upward-references ("../some/foo") but rather
> e.g.
> > "PROJECT_SOURCE_DIR" etc.
>
> How would that work?
>
>
Easiest thing to do here is in each project's CMakeLists.txt file, use a
standard naming
convention to hoist the public include directory up to the superproject.  I
would macro-ize
the dependency definition and building of the dependency header list, like:

in libs/uuid/CMakeLists.txt:

boost_depends_on ( serialization throw_exception )

Which would in turn set:

set ( BOOST_UUID_DEPINCS ${BOOST_SERIALIZATION_HEADERS}
${BOOST_THROW_EXCEPTION_HEADERS} )
(and if those had link libraries, which would be identified by another
variable of some sort, it would add to the link library list needed)

The project itself would set the variable BOOST_UUID_HEADERS as:

set ( BOOST_UUID_HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/include
${BOOST_UUID_DEPINCS} PARENT_SCOPE )

This defines BOOST_UUID_HEADERS one level up - in the "libs" project.  This
variable now contains all of the include
paths needed build anything that depends on uuid.

In each dependent project, adding the following allows for access to the
headers:

boost_depends_on ( uuid )

which as part of the macro would run:

include_directories ( ${BOOST_UUID_HEADERS} )

And obviously back in uuid where it says "boost_depends_on" that also added
include directories for serialization and throw_exception for the uuid
build.

Now here's the really neat thing: the list of subdirectories in
libs/CMakeLists.txt MUST be in dependency order
which FORCES you to remove any cyclic dependencies in the overall project,
which is a big plus!

- Jim