[CMake] add_custom_command and CONFIG-dependent output

[Braden McDaniel]

On Fri, 2014-08-22 at 16:58 -0400, David Cole via CMake wrote:
> Use "${CMAKE_CFG_INTDIR}" in the context of add_custom_command OUTPUT,
> not $<CONFIG>.
> 
> You may also use that in the COMMAND arguments.
> 
> See documentation here:
> http://www.cmake.org/cmake/help/v3.0/variable/CMAKE_CFG_INTDIR.html
> 
> The $<> generator expressions are relatively new, and do not work in
> all contexts that you might expect yet. CMAKE_CFG_INTDIR has been
> around for quite some time, though, and works very well with custom
> commands.

Ah, thanks... Though, I think there may be a general disconnect here:
that is, it seems likely that one would want to construct output with a
pattern composed from generator expressions.  For instance, in a
subsequent rule I attempted to do this:

    set(LIB "$<TARGET_FILE:${LIBRARY_TARGET}>")
    set(STAGED_LIB "${LIB_STAGEDIR}/$<TARGET_FILE_NAME:${LIBRARY_TARGET}>")
    add_custom_command(
        OUTPUT ${STAGED_LIB}
        COMMAND ${CMAKE_COMMAND} -E copy ${LIB} ${STAGED_LIB}
        MAIN_DEPENDENCY ${LIB_STAGEDIR}
    )

... which obviously has the same problem.

While I gather from your comment that something like this might be
possible in the future, is there some other general approach that can be
taken with current CMake?

Braden