[CMake] Custom Command OUTPUTs to understand geenrator expressions?

[Chris Green]

Hi,

I have a case where a custom command produces multiple outputs, at least 
some of which depend on a property of a library target, viz:

   if (BD_WANT_PCM)
     set(PCM_OUTPUT
       $<TARGET_PROPERTY:${dictname}_dict,LIBRARY_OUTPUT_DIRECTORY>/${CMAKE_SHARED_LIBRARY_PREFIX}${dictname}_dict_rdict.pcm)
     if (GD_PCM_OUTPUT_VAR)
       set(${GD_PCM_OUTPUT_VAR} ${PCM_OUTPUT} PARENT_SCOPE)
     endif()
   endif()
   add_custom_command(
     OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${dictname}_dict.cpp
     # Extra outputs commented out until custom_command OUTPUT supports
     # generator flags.
     ${SOURCE_OUTPUT} # ${GD_ROOTMAP_OUTPUT} ${PCM_OUTPUT}
   ...

Here, ${PCM_OUTPUT} needs to be specified to be put in the same 
directory as the library produced for the target ${dictname}_dict, which 
may be something particular to that target rather than its defaulted 
value of ${CMAKE_LIBRARY_OUTPUT_DIRECTORY} or ${LIBRARY_OUTPUT_PATH}. 
Unfortunately, this fails to work as of CMake 3.9.2. Is this something 
which is reasonable to want and/or easy to do. Is there some other way 
to have the desired flexibility?

Thanks for any help,

Chris.