Support Host Functions about js-pdk HOT 4 CLOSED

Since we have a Host global, would it make sense to use a similar approach instead of "extism:host"? Like HostCall.host_func1 or HostCall.host_func2? I also peeked at other PDKs, they are generally light on details on how host function calls are implemented and used other than the default inputString().

If I am a plugin developer, and I want to to call some host_func1 it would be great if I can copy+paste/import some kind of definition so I know for sure what I am calling. But I haven't played with plugins so not sure if that's reasonable suggestion or not.

For exports I see that your code reference looks for a module.exports by eval some JS which seems fairly reasonable to me.
Also see https://github.com/dylibso/pg_extism/blob/main/plugins/chatgpt/script.js#L1 which may or may not be useful.

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Started work on this and we have a new proposal extism/proposals#16

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Yes, that's a good point. I think putting the imports on the Host object or having another global makes sense to continue with. So I'd be open to any of those options.

The tricky issue will still be getting the imports defined into the wasm file. So we'll still need to parse something ahead of time and do a similar trick we do with exports. We could also have some conventional structure you're expected to define as a global in the top of your module. Kind of like how rust works with externs:

#[host_fn]
extern "ExtismHost" {
    fn hello_world(input: String) -> Json<Output>;
}

// ^ that gets expanded to this:
extern "C" {
    fn hello_world(input: i64) -> i64;
}

The compiler will need to know what all the imports are that the plugin needs and what the wasm type signature of each host function is. So it will need to parse the JS (or wherever you want to put these declarations), look for these imports and signatures, then compile in the imports into the wasm binary.

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I believe we can call this done

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