Yes we want to see the doxygen documentation that is inside

#if HAVE_MPI
// code
#endif

[[Imported from SVN: r535]]

doc/doxygen/Doxyfile

@@ -978,13 +978,13 @@ ENABLE_PREPROCESSING   = YES
 # compilation will be performed. Macro expansion can be done in a controlled 
 # way by setting EXPAND_ONLY_PREDEF to YES.
 
-MACRO_EXPANSION        = NO
+MACRO_EXPANSION        = YES
 
 # If the EXPAND_ONLY_PREDEF and MACRO_EXPANSION tags are both set to YES 
 # then the macro expansion is limited to the macros specified with the 
 # PREDEFINED and EXPAND_AS_PREDEFINED tags.
 
-EXPAND_ONLY_PREDEF     = NO
+EXPAND_ONLY_PREDEF     = YES
 
 # If the SEARCH_INCLUDES tag is set to YES (the default) the includes files 
 # in the INCLUDE_PATH (see below) will be search if a #include is found.
@@ -1012,7 +1012,7 @@ INCLUDE_FILE_PATTERNS  =
 # undefined via #undef or recursively expanded use the := operator 
 # instead of the = operator.
 
-PREDEFINED             = DOXYGEN
+PREDEFINED             = DOXYGEN HAVE_MPI:=1
 
 # If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then 
 # this tag can be used to specify a list of macro names that should be expanded.