[CMake] generator-expressions + pch -> need new magic

[Evgeniy Dushistov]

I found workaround for that problem,
I add to this loop:
foreach(flag ${MY_DEFS})
     list(APPEND gcc_flags  "-D${flag}")
endforeach()

such code:
  foreach(flag ${PL_COMP_DEFS})
    string(FIND ${flag} "$<" find_res)
    if (find_res EQUAL 0)
      list(APPEND gcc_flags "$<$<BOOL:${flag}>:-D$<JOIN:${flag}, -D>>")
    else ()
      list(APPEND gcc_flags  "-D${flag}")
    endif ()
  endforeach()

but may there is better solution?

On Sun, Oct 5, 2014 at 10:25 AM, Evgeniy Dushistov <dushistov at gmail.com> wrote:
> Hi,
> in my project I used such magic code for precompiled headers support
> (gcc,clang only):
>
> #take gcc_flags from
>                               ${CMAKE_CXX_FLAGS}
> ${CMAKE_CXX_FLAGS_${_build_type}}
>            get_target_property(... COMPILE_FLAGS)
>                          get_directory_property(...
> INCLUDE_DIRECTORIES)                               foreach(flag
> ${MY_INCLUDES})
>     list(APPEND gcc_flags  "-I" "${pl_flag}")
>                      endforeach()
>
> get_directory_property(... COMPILE_DEFINITIONS)
> foreach(flag ${MY_DEFS})
>                               list(APPEND gcc_flags  "-D${pl_flag}")
>                                               endforeach()
>
>            get_directory_property(...
> COMPILE_DEFINITIONS_${_build_type})       add_custom_command(...
> ${gcc_flags} ...)
> All works fine, until cmake-3.0 with cmake-generator-expressions.
>      With cmake-3.0 COMPILE_DEFINITIONS return something like this:
> $<$<NOT:$<CONFIG:Debug>>:QT_NO_DEBUG>
>
> This is empty string on compilation stage, not on not configuration
> stage. So "gcc" is called like this: "gcc -D<empty>" and give error.
> So question is it possible to evaluate "generator-expressions" within
> CMakeLists.txt? Or may be in cmake 3.x there another is way to extract
> compilation
> flags without such magic as above?