spaCy's implemented in Cython, which compiles into C++. So, the end-state at the moment is a .so object that expects to be loaded into Python.
Now, you can instead tell Cython to compile into standalone objects, so that they can be imported from C/C++ code. I'm not well versed on this, but if you can call into C/C++ libraries easily from Rust, you should be able to call into spaCy.
You'll miss some of the niceties from the Python layer, but the C-level API is pretty well behaved. So, you should be able to get by okay.
Curious: since spaCy is a commercial project (I know that it is open source), did you consider writing it in C or C++, it would make binding to other languages a lot easier. I can imagine that importing the Python runtime can be problematic in some projects. Also, I assume that you will see some Python types in the API when you want to call the parser from C?
(My own NN dependency parser is written in Go, since it's mostly for research, but if I wanted to make it embeddable, I'd have implemented it in C++ or Rust with a C API.)
Well, I like writing in Cython, and I figured I was better off pleasing some people (Python) a lot before trying to please a lot of people a little. It won't be hard to port to C++ when the time comes.
Now, you can instead tell Cython to compile into standalone objects, so that they can be imported from C/C++ code. I'm not well versed on this, but if you can call into C/C++ libraries easily from Rust, you should be able to call into spaCy.
You'll miss some of the niceties from the Python layer, but the C-level API is pretty well behaved. So, you should be able to get by okay.