Making non-standard OS checks in cmake?

[Raphael Kubo da Costa]

On Friday 01 January 2010 16:43:10 Pau Garcia i Quiles wrote:
> On Fri, Jan 1, 2010 at 7:22 PM, Raphael Kubo da Costa <kubito at gmail.com> 
wrote:
> > On Friday 01 January 2010 16:01:14 Alexander Neundorf wrote:
> >> On Friday 01 January 2010, Raphael Kubo da Costa wrote:
> >> > Hey there,
> >> > 
> >> > As you can see on my.cdash.org, both kdeadmin and kdenetwork fail to
> >> > build
> >> > 
> >> > cleanly on FreeBSD:
> >> >  * kdeadmin/kuser's CMakeLists.txt's check for the need to link
> >> > against -
> >> > 
> >> > lcrypt is broken on FreeBSD,  since the crypt() function is defined in
> >> > unistd.h, not crypt.h, even though -lcrypt still must be passed to the
> >> > compiler
> >> 
> >> Does crypt.h also exist ?
> >> You could also try check_symbol_exists() (
> >> http://www.cmake.org/cmake/help/cmake2.6docs.html#module:CheckSymbolExis
> >> ts ) to find out whether crypt() is in unistd.h or crypt.h
> > 
> > No, crypt.h doesn't exist. Would check_symbol_exists() not work then? How
> > about using check_library_exists()?
> 
> Something like this should work in all cases:
> 
> find_file( CRYPT_HEADER crypt.h )
> find_library( CRYPT_LIBRARY crypt )
> 
> if( NOT CRYPT_HEADER )
>   set( CRYPT_HEADER unistd.h )
> endif( NOT CRYPT_HEADER)
> 
> include(CheckFunctionExists)
> include(CheckLibraryExists)
> 
> set(CMAKE_REQUIRED_INCLUDES ${CRYPT_HEADER})
> check_function_exists(crypt CRYPT3_EXISTS)
> if(NOT CRYPT3_EXISTS)
>   if(CRYPT_LIBRARY)
>     set(CMAKE_REQUIRED_LIBRARIES "crypt")
>     set(CMAKE_REQUIRED_INCLUDES ${CRYPT_HEADER})
>     check_function_exists(crypt CRYPT3_EXISTS_WITH_LIBRARY)
>   endif(CRYPT_LIBRARY)
> endif(NOT CRYPT3_EXISTS)
> 
> if(CRYPT3_EXISTS OR CRYPT3_EXISTS_WITH_LIBRARY)
>   # add_executable, or whatever you should do if crypt(3) is available
> endif(CRYPT3_EXISTS OR CRYPT3_EXISTS_WITH_LIBRARY)
> 
> if( CRYPT3_EXISTS_WITH_LIBRARY )
>   target_link_libraries( yourtarget ${CRYPT_LIBRARY} )
> endif( CRYPT3_EXISTS_WITH_LIBRARY )
> 
> It's probably possible to simplify it but I'm not in the mood just now :-)

Is this really necessary? What if we just check if libcrypt exists and link to 
it if it does?