The goal here is to reduce the number of files that need to be edited when
adding a new node. To register a node, one currently has to add a line to
`node_geometry_register.cc` and `node_geometry_register.hh` (for geometry
nodes). Those files can be generated automatically.
There is a new `NOD_REGISTER_NODE` macro that nodes can use to register
themselves. The macro is then discovered by `discover_nodes.py` that generates
code that calls all the registration functions. The script also works when the
register functions are in arbitrary namespaces. This allows simplifying the node
code as well.
In the past I tried a few times to get auto-registration working without resorting to
code generation, but that never ended up working. The general idea for that would
be to use non-trivial initialization for static variables. The issue always ends up
being that the linker just discards those variables, because they are unused and it
doesn't care if there are side effects in the initialization.
Related discussion regarding using Python for code generation:
https://devtalk.blender.org/t/code-generation-with-python/30558
Pull Request: https://projects.blender.org/blender/blender/pulls/110686
19912457c6