[CMake] Mixing non-CMake ExternalProjects using Visual Studio

[Braden McDaniel]

When mixing a CMake Visual Studio build that has ExternalProjects (that is, via ExternalProject_Add) that use non-CMake makefile builds, how does one resolve the mismatch between the *_<config> variables (CMAKE_CXX_FLAGS_RELEASE, etc.)?

Specifically, how do I propagate the build flags in the *_<config> variables down to the ExternalProject?  I can't seem to find a way in CMake that will let me pick which variable to propagate (that is, CMAKE_CXX_FLAGS_DEBUG when I'm building the Debug configuration, CMAKE_CXX_FLAGS_RELEASE when building the Release configuration, etc.).

One option seems to be just to build the makefile-based ExternalProject four times--one for each configuration CMake generates in its project files.  But that, too, has a problem: what if the makefile-based ExternalProject has a dependency on another ExternalProject with a CMake build?

Are there any good solutions to these sorts of problems?

-- 
Braden McDaniel
braden at endoframe.com