Make MOAB a proper optional dependency

CMakeLists.txt

@@ -1,9 +1,9 @@
 cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
 project(openmc C CXX)
 
-option(XDG_MOAB_BACKEND "Enable MAOB mesh" ON)
-option(XDG_MFEM_BACKEND "Enable MFEM mesh" OFF)
-option(XDG_LIBMESH_BACKEND "Enable libMesh mesh" OFF)
+option(XDG_ENABLE_MOAB "Enable support for the MOAB mesh library" ON)
+option(XDG_ENABLE_MFEM "Enable support for the MFEM mesh library" OFF)
+option(XDG_ENABLE_LIBMESH "Enable support for the libMesh mesh library" OFF)
 option(XDG_BUILD_TESTS "Enable C++ unit testing" ON)
 
 if(NOT CMAKE_BUILD_TYPE)
@@ -14,7 +14,9 @@ endif()
 set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 
 # require MOAB for now
+if (XDG_ENABLE_MOAB)
 find_package(MOAB REQUIRED HINTS ${MOAB_DIR})
+endif()
 
 # use Embree for CPU ray tracing
 find_package(embree 3.6.1 REQUIRED)
@@ -46,12 +48,16 @@ src/plucker.cpp
 src/ray_tracing_interface.cpp
 src/triangle_ref.cpp
 src/util/str_utils.cpp
+)
 
+if (XDG_ENABLE_MOAB)
+list(APPEND xdg_sources
 # MOAB
 src/moab/mesh_manager.cpp
 src/moab/direct_access.cpp
 src/moab/metadata.cpp
 )
+endif()
 
 add_library(xdg SHARED ${xdg_sources})
 
@@ -76,6 +82,6 @@ target_include_directories(xdg
 
 target_link_libraries(xdg embree fmt::fmt)
 
-if (XDG_MOAB_BACKEND)
+if (XDG_ENABLE_MOAB)
   target_link_libraries(xdg MOAB)
 endif()

tests/CMakeLists.txt

@@ -8,9 +8,12 @@ test_closest
 test_ray_fire
 test_mesh_internal
 test_xdg_interface
-test_moab
 )
 
+if (XDG_ENABLE_MOAB)
+    list(APPEND TEST_NAMES test_moab)
+endif()
+
 foreach(test ${TEST_NAMES})
     add_executable(${test} ${test}.cpp)
     target_link_libraries(${test} xdg Catch2::Catch2WithMain)