[cmake][bugfix] Make CMake Doxygen creation work for modules without Doxylocal

When creating Doxygen documentation, CMake currently assumes that all modules have a Doxylocal file, which is in fact only present in dune-common right now. That file is then used as both a dependency and a file reading input, causing CMake errors.

This patch fixes the problem by testing for the presence of Doxylocal and only including it in the build process if it was found.

cmake/modules/DuneDoxygen.cmake

@@ -43,11 +43,23 @@ add_custom_target(doxygen_install)
 # Doxyfile[.in] files needed to doxygen.
 MACRO (prepare_doxyfile)
   message(STATUS "using ${DOXYSTYLE_FILE} to create doxystyle file")
-  set(make_doxyfile_command ${CMAKE_COMMAND} -D DOT_TRUE=${DOT_TRUE} -D DUNEWEB_TRUE=\# -D ProjectName=${ProjectName} -D DUNE_MOD_VERSION=${DUNE_MOD_VERSION} -D DOXYSTYLE=${DOXYSTYLE_FILE}  -D DOXYLOCAL=${CMAKE_CURRENT_SOURCE_DIR}/Doxylocal -D abs_top_srcdir=${CMAKE_SOURCE_DIR} -D srcdir=${CMAKE_CURRENT_SOURCE_DIR} -D top_srcdir=${CMAKE_SOURCE_DIR} -P ${SCRIPT_DIR}/CreateDoxyFile.cmake)
-  add_custom_command (OUTPUT Doxyfile.in Doxyfile
-    COMMAND ${make_doxyfile_command}
-    COMMENT "Creating Doxyfile.in"
-    DEPENDS ${DOXYSTYLE_FILE} ${CMAKE_CURRENT_SOURCE_DIR}/Doxylocal)
+
+  # check whether module has a Doxylocal file
+  file(_DOXYLOCAL PATHS ${CURRENT_SOURCE_DIR} NO_DEFAULT_PATH)
+
+  if(_DOXYLOCAL)
+    set(make_doxyfile_command ${CMAKE_COMMAND} -D DOT_TRUE=${DOT_TRUE} -D DUNEWEB_TRUE=\# -D ProjectName=${ProjectName} -D DUNE_MOD_VERSION=${DUNE_MOD_VERSION} -D DOXYSTYLE=${DOXYSTYLE_FILE}  -D DOXYLOCAL=${CMAKE_CURRENT_SOURCE_DIR}/Doxylocal -D abs_top_srcdir=${CMAKE_SOURCE_DIR} -D srcdir=${CMAKE_CURRENT_SOURCE_DIR} -D top_srcdir=${CMAKE_SOURCE_DIR} -P ${SCRIPT_DIR}/CreateDoxyFile.cmake)
+    add_custom_command (OUTPUT Doxyfile.in Doxyfile
+      COMMAND ${make_doxyfile_command}
+      COMMENT "Creating Doxyfile.in"
+      DEPENDS ${DOXYSTYLE_FILE} ${CMAKE_CURRENT_SOURCE_DIR}/Doxylocal)
+  else()
+    set(make_doxyfile_command ${CMAKE_COMMAND} -D DOT_TRUE=${DOT_TRUE} -D DUNEWEB_TRUE=\# -D ProjectName=${ProjectName} -D DUNE_MOD_VERSION=${DUNE_MOD_VERSION} -D DOXYSTYLE=${DOXYSTYLE_FILE}  -D DOXYLOCAL=${CMAKE_CURRENT_SOURCE_DIR}/Doxylocal -D abs_top_srcdir=${CMAKE_SOURCE_DIR} -D top_srcdir=${CMAKE_SOURCE_DIR} -P ${SCRIPT_DIR}/CreateDoxyFile.cmake)
+    add_custom_command (OUTPUT Doxyfile.in Doxyfile
+      COMMAND ${make_doxyfile_command}
+      COMMENT "Creating Doxyfile.in"
+      DEPENDS ${DOXYSTYLE_FILE})
+  endif()
   add_custom_target(Doxyfile DEPENDS Doxyfile.in Doxyfile)
 ENDMACRO (prepare_doxyfile)