[Discuss-gnuradio] cmake module issue

[Michael Dickens]

I received a report this morning that gr-osmosdr was not configuring correctly 
in MacPorts; not able to find GNU Radio.  Trying this myself, I can recreate 
the issue.  After some investigation, the issue is somewhere between a cmake 
bug, and GR issue, and "my bad".  I've read through the cmake documents on this 
topic as well as tried what cmake printed as its error message, but none of 
those make sense or work.  I can work around the issue, but I think there needs 
to be better integration between GR and cmake.

What happened is that yesterday (Tuesday, 15-Oct-2013) I pushed a change which 
moved the GR cmake files from their default install location, 
${prefix}/lib/cmake, to a common (across all ports) cmake location: 
${prefix}/share/cmake/modules/.  After install, I moved ${prefix}/lib/cmake/* 
into ${prefix}/share/cmake/modules/ -> which means there are 2 directories now: 
gnuradio and volk.  I thought that this is the way cmake should like things, 
and I know it is the way MacPorts prefers non-cmake-provided cmake modules to 
be installed.

But, cmake does not like this setup; it cannot find GR using this setup.  After 
testing a bunch, I find that there are 2 configurations cmake likes:

1) having "FindGnuradio.cmake" in a directory in CMAKE_MODULE_PATH (whether as 
an actual file or linked).

2) having "GnuradioConfig.cmake" in a top-level directory in some other cmake 
search path -- I don't have a variable name for this one, but it seems to 
include "${prefix}/lib/cmake:${prefix}/share/cmake", where the "cmake-X.Y" is 
installed (and known) by cmake itself; seems like it is like each value in 
CMAKE_MODULE_PATH but with "[Mm]odules" removed from the end.

GR provides just GnuradioConfig.cmake, not FindGnuradio.cmake.  Hence, I have 
to place the "gnuradio" directory in a top-level directory, not in a modules 
directory.  It also seems to work that I can link GnuradioConfig.cmake to 
FindGnuradio.cmake so long as this link is in a directory in CMAKE_MODULE_PATH.

So ... I'm not sure what to make of this behavior by cmake.  I will fix the way 
these files are installed within MacPorts, for now, but I hope we come up with 
a better solution. - MLD