3.7 backport: #3875

Can you be more specific on the failures you are seeing?

Sure, for (3.7) with gr-osmosdr (with the last version of gr-osmosdr that supports 3.7):

gr-osmosdr> /build/gr-osmosdr/swig/osmosdr_swig.i:8: Error: Unable to find 'gnuradio.i'
gr-osmosdr> make[2]: *** [swig/CMakeFiles/osmosdr_swig_swig_2d0df.dir/build.make:117: swig/osmosdr_swig_swig_2d0df] Error 1
gr-osmosdr> make[2]: *** Deleting file 'swig/osmosdr_swig_swig_2d0df'
gr-osmosdr> make[1]: *** [CMakeFiles/Makefile2:358: swig/CMakeFiles/osmosdr_swig_swig_2d0df.dir/all] Error 2
gr-osmosdr> make[1]: *** Waiting for unfinished jobs....

It seems to me like the OOT should not be building swig related stuff at all if it is being built with -DENABLE_PYTHON=OFF

https://github.com/osmocom/gr-osmosdr/blob/gr3.7/CMakeLists.txt#L240

I wonder why its doing swig stuff at all... are you sure this is being passed into the OOT?

There should be no reason for swig if python is not enabled. Seems like this should be fixed on the OOT side

Well if python and swig are available during build of gr-osmosdr, it assumes (righteously I suppose) that GNUradio was built with swig files as well. And, if I don't add python and swig to the build of gr-osmosdr, and I build it with a gnuradio without python support, it builds fine, as expected. Hence it means we should not enable python support for gr-osmosdr when it's built with a gnuradio without python support as well. I'll close this and the other PR as they are not justified indeed. Thanks for the feedback.