Support list of paths in component bindgen macro

[lwansbrough]

wit-bindgen includes the option to provide a list of paths for the wit sources. This makes it more practical to satisfy the requirements of imports from other packages. Enabling this behaviour for the component bindgen macro would be helpful.

wit-bindgen docs:

// Path to parse WIT and its dependencies from. Defaults to the `wit`
// folder adjacent to your `Cargo.toml`.
//
// This parameter also supports the form of a list, such as:
// ["../path/to/wit1", "../path/to/wit2"]
// Usually used in testing, our test suite may want to generate code
// from wit files located in multiple paths within a single mod, and we
// don't want to copy these files again.
path: "../path/to/wit",

[alexcrichton]

Thanks for the report! To link things here this was implemented in wit-bindgen in bytecodealliance/wit-bindgen#1003 and I think it'd be reasonable to copy over a similar structure into Wasmtime as well. @lwansbrough would you be interested in creating a PR perhaps?

[lwansbrough]

@alexcrichton I'll see what I can do.

I was looking through that commit and this looks like a bug to me. https://github.com/bytecodealliance/wit-bindgen/blob/3e3877da85daf1ed98bd1aee7007e496461c3bd1/crates/guest-rust/macro/src/lib.rs#L215

Line 237 passes root.join("wit") which would mean root is joined to root.

[alexcrichton]

Good catch! Semantically that'll work out ok since "/a".join("/b") yields "/b", so the end result is the same. That being said it's unnecessarily complex, and just passing in "wit" instead of root.join("wit") should also work and be cleaner.

[MarinPostma]

Will this enable importing transitive dependencies of the package? Say I am generating binding for package A, but package A includes package B in a different directory, should I just be able to add the path to B and have it all work?

[alexcrichton]

@MarinPostma I believe so yeah, but if it doesn't let me know!

[MarinPostma]

I'll give it a try then :)