Help with subsurface port.

Hi folks,

I'm working on a package for Subsurface, https://subsurface-divelog.org.
It now compiles fine (some pending stuff upstream for it) and I've been
using it for a while on OpenBSD by way of a modified version of its
baked-in build script.

The question is as follows. I think I can get all the package parts
right for the cmake. Unfortunately, the build depends on a
specially-modified version of a library, libdivecomputer, which it
downloads and installs in-band.

I've already made a libdivecomputer port that I've let rot (I'll
reintroduce it), so my thought is to make a libdivecomputer-subsurface
package that installs into /usr/local/{lib,include}/subsurface. Then
depend upon the libdivecomputer-subsurface package when compiling
subsurface. This prevents the in-band build.

Does that sound like an appropriate approach? The new package would
only be used by subsurface, which seems backward, but I don't know of
the correct ports magic to download, unpack, and install during the port
creation.

Thoughts?

Kristaps