Issue with dependency propagation for object libraries

[kennyweiss]

There might be a bug with how blt_add_library propagates dependencies for object libraries.
My specific case is for an object library that depends on an imported library with its own internal dependencies.

Specifically, I have an axom configuration that depends on RAJA with RAJA_ENABLE_ROCTX = ON.

• The RAJA import has a RAJA target that depends on the RAJA::roctx target.
• Axom's core component is an object library. When invoking blt_add_library, it gets the RAJA dependency, but does not eventually get include paths from RAJA::roctx

Details and links:

• RAJA_ENABLE_ROCTX option: https://github.com/LLNL/RAJA/blob/093bc446fdde333749a13ceca262c09ca3ad1049/cmake/SetupRajaOptions.cmake#L12
• Axom's setup for the core component: https://github.com/LLNL/axom/blob/1f86e245684480c1d9bcfe88f50011b0bb280e6d/src/axom/core/CMakeLists.txt#L96-L116
• Partial dependency setup for object libraries in blt_add_library:

  blt/cmake/BLTMacros.cmake

  Lines 635 to 646 in 8c22999

  	if ( ${arg_OBJECT} )
  	set(_lib_type "OBJECT")
  	blt_register_library( NAME ${arg_NAME}
  	DEPENDS_ON ${arg_DEPENDS_ON}
  	INCLUDES ${arg_INCLUDES}
  	OBJECT TRUE
  	DEFINES ${arg_DEFINES} )
  	elseif ( ${_build_shared_library} )
  	set(_lib_type "SHARED")
  	else()
  	set(_lib_type "STATIC")
  	endif()

• More dependency setup in blt_add_library:

  blt/cmake/BLTMacros.cmake

  Lines 691 to 693 in 8c22999

  	blt_setup_target( NAME ${arg_NAME}
  	DEPENDS_ON ${arg_DEPENDS_ON}
  	OBJECT ${arg_OBJECT})

• Possibly relevant: blt_expand_dependencies only applies to (pseudo)-targets created by blt_register_library:

  blt/cmake/BLTPrivateMacros.cmake

  Lines 329 to 339 in 8c22999

  	foreach( dependency ${_current_deps_to_process} )
  	string(TOUPPER ${dependency} uppercase_dependency )
  	if ( DEFINED _BLT_${uppercase_dependency}_DEPENDS_ON )
  	foreach(new_dependency ${_BLT_${uppercase_dependency}_DEPENDS_ON})
  	# Don't add duplicates
  	if (NOT ${new_dependency} IN_LIST _expanded_DEPENDS_ON)
  	list(APPEND _deps_to_process ${new_dependency})
  	endif()
  	endforeach()
  	endif()
  	endforeach()

• Temporary workaround in axom: Bugfix for RAJA's optional RAJA::roctx dependency axom#1002