[cmake-developers] Language generator expressions

[Brad King]

On 05/17/2013 09:33 AM, Stephen Kelly wrote:
>  add_library(foo a.c b.cpp c.c d.cpp)
>  target_compile_definitions(foo 
>    PRIVATE
>      $<$<COMPILE_LANGUAGE:C>:C_ONLY>
>      $<$<COMPILE_LANGUAGE:CXX>:CXX_ONLY>
>      $<$<LINK_LANGUAGE:CXX>:LINK_AS_CXX>
>  )
> 
> a.c and c.c get compiled with -DC_ONLY, b.cpp and d.cpp get compiled with 
> CXX_ONLY, and all get compiled with LINK_AS_CXX.

In order to implement that in the IDE generators you will need to generate
per-source flags for every source file with the corresponding target-wide
per-language flags.

* VS: Once you have per-source flags then VS can no longer invoke the
  "cl" compiler with multiple sources on the command line so compile
  times will significantly suffer.

* Xcode: There is no way to express per-source per-config flags
  (or at least there wasn't last time I checked a few years ago)

We already gloss over the difference between CMAKE_C_FLAGS and
CMAKE_CXX_FLAGS in the IDE generators by using the one corresponding
to the target link language IIRC.

-Brad