cmake ignore doxygen option when not a standalone build (#488)

CMakeLists.txt

@@ -191,29 +191,33 @@ endif()
 #=============================================================================
 # Doxygen
 #
-option(BUILD_DOXYGEN "Build doxygen documentation" OFF)
+# Only in standalone build
-
+if(CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR)
-if (BUILD_DOXYGEN)
-	find_package(Doxygen)
-	if (DOXYGEN_FOUND)
-		# set input and output files
-		set(DOXYGEN_IN ${CMAKE_SOURCE_DIR}/docs/Doxyfile.in)
-		set(DOXYGEN_OUT ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile)
-
-		# request to configure the file
-		configure_file(${DOXYGEN_IN} ${DOXYGEN_OUT} @ONLY)
-
-		# note the option ALL which allows to build the docs together with the application
-		add_custom_target(doxygen ALL
-			COMMAND ${DOXYGEN_EXECUTABLE} ${DOXYGEN_OUT}
-			WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
-			COMMENT "Generating documentation with Doxygen"
-			DEPENDS
-			VERBATIM
-			USES_TERMINAL
-		)
 
-	else()
+	option(BUILD_DOXYGEN "Build doxygen documentation" OFF)
-		message(FATAL_ERROR "Doxygen needs to be installed to generate documentation")
+	
+	if (BUILD_DOXYGEN)
+		find_package(Doxygen)
+		if (DOXYGEN_FOUND)
+			# set input and output files
+			set(DOXYGEN_IN ${CMAKE_CURRENT_SOURCE_DIR}/docs/Doxyfile.in)
+			set(DOXYGEN_OUT ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile)
+	
+			# request to configure the file
+			configure_file(${DOXYGEN_IN} ${DOXYGEN_OUT} @ONLY)
+	
+			# note the option ALL which allows to build the docs together with the application
+			add_custom_target(doxygen ALL
+				COMMAND ${DOXYGEN_EXECUTABLE} ${DOXYGEN_OUT}
+				WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+				COMMENT "Generating documentation with Doxygen"
+				DEPENDS
+				VERBATIM
+				USES_TERMINAL
+			)
+	
+		else()
+			message(FATAL_ERROR "Doxygen needs to be installed to generate documentation")
+		endif()
 	endif()
 endif()