Alternate build directory for CMake-based port?

[Joshua Root]

On 2012-8-24 00:39 , Kevin Reid wrote:
> I am interested in getting the GNU Radio ports (gnuradio-*) updated to the latest version. (Relevant ticket: <https://trac.macports.org/ticket/31475>. The maintainer has acknowledged the problem but no work has been done for 11 months.) I have not seriously attempted to work on portfiles before.
> 
> GNU Radio 3.6.* has switched exclusively to a CMake-based build system. For the most part, I have been able to simply apply the cmake PortGroup and modify the configuration parameters to CMake style.
> 
> However, GNU Radio also insists that the build directory be different from the source directory; the CMakeLists.txt file contains:
> 
> if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_BINARY_DIR})
>     message(FATAL_ERROR "Prevented in-tree build. This is bad practice.")
> endif(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_BINARY_DIR})
> 
> I could of course patch out this condition, but that seems unnecessarily fragile if it even works. How can I tell MacPorts to use distinct source and build directories for a CMake-based port?
> 
> The official build instructions are to do
>   (in gnuradio source)
>   mkdir build
>   cd build
>   cmake ../
>   make
> but since MacPorts takes care of these commands via its own infrastructure I don't know where to "just" insert a cd command and tweak the pathnames.

Sure, something like this should do it:

worksrcdir    ${worksrcdir}/build
post-extract {
    file mkdir ${worksrcpath}
}

- Josh