adding doxygen build

CMakeLists.txt

@@ -1,6 +1,13 @@
+# This is the main CMake file for fv3atm.
+#
+# Mark Potts, Kyle Gerheiser, Alex Richert
+cmake_minimum_required(VERSION 3.19)
+
+# Handle user build options.
+option(ENABLE_DOCS "Enable generation of doxygen-based documentation." OFF)
+
 # Enable CI build & unit testing:
 if(BUILD_TESTING)
-  cmake_minimum_required(VERSION 3.19)
   project(fv3atm VERSION 1.0 LANGUAGES C CXX Fortran)
   include(ci/CMakeLists.txt)
 endif()
@@ -141,6 +148,12 @@ if(OPENMP)
   target_link_libraries(fv3atm PUBLIC OpenMP::OpenMP_Fortran)
 endif()
 
+# Determine whether or not to generate documentation.
+if(ENABLE_DOCS)
+  find_package(Doxygen REQUIRED)
+endif()
+add_subdirectory(docs)  
+
 ###############################################################################
 ### Install
 ###############################################################################

docs/CMakeLists.txt

@@ -0,0 +1,17 @@
+# This is the CMake file for building the docs directory of fv3atm.
+#
+# Ed Hartnett 12/28/23
+
+IF(ENABLE_DOCS)
+
+  # Create doxyfile.
+  SET(abs_top_srcdir "${CMAKE_SOURCE_DIR}")
+  SET(abs_top_builddir "${CMAKE_BINARY_DIR}")
+  CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/Doxyfile.in ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
+  ADD_CUSTOM_TARGET(doc ALL
+    ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
+    WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+    COMMENT "Generating API Documentation with Doxygen" VERBATIM)
+
+ENDIF(ENABLE_DOCS)
+