Make Rust based .wasm module take an import for a host function.

[JustAnotherCodemonkey]

I'm trying to learn how to use WASM modules for mods for my game and have run into an issue for which I can not find documentation: I can provide a host function using the Wasmer crate to use as an import for the module but if I'm writing the WASM module in Rust and compiling to WASM, how do I get access to that host function in the Rust code for the WASM module?