I was snooping around in FindBoost.cmake and found

   IF (Boost_${basename}_LIBRARY_DEBUG AND Boost_${basename}_LIBRARY_RELEASE)
      # if the generator supports configuration types then set
      # optimized and debug libraries, or if the CMAKE_BUILD_TYPE has a value
      IF (CMAKE_CONFIGURATION_TYPES OR CMAKE_BUILD_TYPE)
        SET(Boost_${basename}_LIBRARY optimized ${Boost_${basename}_LIBRARY_RELEASE} debug ${Boost_${basename}_LIBRARY_DEBUG})
      ELSE(CMAKE_CONFIGURATION_TYPES OR CMAKE_BUILD_TYPE)
        # if there are no configuration types and CMAKE_BUILD_TYPE has no value
        # then just use the release libraries
        SET(Boost_${basename}_LIBRARY ${Boost_${basename}_LIBRARY_RELEASE} )
      ENDIF(CMAKE_CONFIGURATION_TYPES OR CMAKE_BUILD_TYPE)
      SET(Boost_${basename}_LIBRARIES optimized ${Boost_${basename}_LIBRARY_RELEASE} debug ${Boost_${basename}_LIBRARY_DEBUG})
    ENDIF (Boost_${basename}_LIBRARY_DEBUG AND Boost_${basename}_LIBRARY_RELEASE)

Note the Boost_${basename}_LIBRARY

This was/is a result of a rogue find_package(Boost ...) which was setting ${Boost_FILESYSTEM_LIBRARY} :

find_package( Boost REQUIRED COMPONENTS system filesystem  NO_MODULE )

Now that this has been removed:

MESSAGE( "Boost_FILESYSTEM_LIBRARY = " ${Boost_FILESYSTEM_LIBRARY} )

now returns

Boost_FILESYSTEM_LIBRARY =


which I am not sure is a step in the right direction, it may in fact be a step sideways and one step backwards.

I am now snooping though BoostCore.cmake.... Would be nice if BoostCore would generate these targets... maybe it does.  And I thought Boost.Build V2 was bad.

Brian