[CMake] Re: CMake script return a value

[Brandon J. Van Every]

Brandon J. Van Every wrote:
> Can a CMake script invoked with
>
> EXECUTE_PROCESS(
>  COMMAND ${CMAKE_COMMAND} -P myscript.cmake
>  RESULT_VARIABLE myresult
> )
>
> return a value?  I don't really want to use stdout.  I need that for 
> status messages.  I could regex the stdout to extract a decorated 
> string, but that's bletcherous.  What I want is to do something like 
> RETURN(${value}) and have RESULT_VARIABLE pick it up.

I realized a further problem, that ADD_CUSTOM_COMMAND and 
ADD_CUSTOM_TARGET can't have EXECUTE_PROCESS in them.  They can only 
call scripts, and the scripts do not return values.  So, there's no way 
to directly return a value from a script to a build rule.

To get around this, I have my script write out a file, and I denote that 
file as the output of a custom build rule, i.e.

ADD_CUSTOM_COMMAND(
  DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/ResultFile
  COMMAND ${CMAKE_COMMAND} -P myscript.cmake
)

Other custom commands can invoke scripts that read the ResultFile.  Data 
floats around in a universe of scripts and files, driven by build rules 
that don't know what's going on.  It's awkward having this separation, 
between build rules and scripts, but it's workable.  Doesn't feel very 
nice compared to using a proper scripting language though.


Cheers,
Brandon Van Every