Hi Leo and thank you for explaining. And hi again guix-devel.

I've now rewritten the file according to your comments except that its
still its own file/module, something I'll fix later.

Now I'm stuck trying to figure out a build error after going from the
tarball release through url-fetch to the non-recursive git-clone download.
CMake finds the package OpenCV when it runs, removing OpenCV from the
package inputs results in an error from CMake (as expected). But the build
fails during the build phase with the following error:

> make[2]: *** No rule to make target 'opencv_core-NOTFOUND', needed by
'libnomacsCore.so.3.16.0'.  Stop.

I've not found any relevant mentions of opencv_core in the source code. I
tried adding monkeying about with the CMakeLists a little to no avail. Also
looked at what Debian does to their package but found nothing that I
thought to be relevant:
https://sources.debian.org/src/nomacs/3.12.0+dfsg-3/debian/

I've attached the new package source.