rust-wasm export cannot find imported handle types

[sunfishcode]

This repository:

https://github.com/sunfishcode/import-export-demo

contains a wit-bindgen project which imports provider.wit:

resource thing {
    frob: function()
}

and exports runner.wit:

use { thing } from provider

doit: function(it: thing)

in a simple Rust program:

wit_bindgen_rust::import!("provider.wit");
wit_bindgen_rust::export!("runner.wit");

struct Exports;

impl runner::Runner for Exports {
    fn doit(it: provider::Thing) {
        it.frob()
    }
}

It currently gets this error:

$ cargo build --target=wasm32-wasi
   Compiling import-export-demo v0.0.0 (/home/sunfish/import-export-demo)
error[E0412]: cannot find type `Thing` in module `super`
 --> src/lib.rs:2:1
  |
2 | wit_bindgen_rust::export!("runner.wit");
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not found in `super`
  |
  = note: consider importing this struct:
          crate::provider::Thing
  = note: this error originates in the macro `wit_bindgen_rust::export` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0412]: cannot find type `Runner` in module `super`
 --> src/lib.rs:2:1
  |
2 | wit_bindgen_rust::export!("runner.wit");
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not found in `super`
  |
  = note: consider importing this trait:
          crate::runner::Runner
  = note: this error originates in the macro `wit_bindgen_rust::export` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0412]: cannot find type `Runner` in module `super`
 --> src/lib.rs:2:1
  |
2 | wit_bindgen_rust::export!("runner.wit");
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not found in `super`
  |
  = note: this error originates in the macro `wit_bindgen_rust::export` (in Nightly builds, run with -Z macro-backtrace for more info)

Looking at the code in gen-rust, I see methods like handle_in_super and handle_projection which look like they're related to this, but it's not clear to me what they need to do here.

[Cyborus04]

Looking at it with cargo expand, it looks like the expanded code makes no reference to the "provider" module (how would it know where it is?) so would it possible to define the expected imports in the macro? i.e.:

wit_bindgen_rust::export!("runner.wit", "provider::thing" = provider::Thing);

or

wit_bindgen_rust::export!("runner.wit", provider { "thing" = provider::Thing });

[alexcrichton]

In general resources-in-other-modules isn't really well supported in probably any of the bindings generators right now. This is something I haven't really devoted much thought to and figured we'd fix things later as they came up and became more imporant. Basically to say that this is largely unimplemented right now and that's expected.

As for things like handle_projection that's for import/export distinctions where sometimes resources are projected associated types from a trait and other times they're a locally defined type.

I think we'd probably want to first decide how this should look in Rust and it presumably wouldn't be too too hard to implement the generator afterwards.

[Liamolucko]

so would it possible to define the expected imports in the macro? i.e.:

wit_bindgen_rust::export!("runner.wit", "provider::thing" = provider::Thing);

or

wit_bindgen_rust::export!("runner.wit", provider { "thing" = provider::Thing });

I think that's a good idea, but it might be simpler to just reference the module as a whole, e.g.:

wit_bindgen_rust::export!("runner.wit", "provider" = some_crate::some_module::provider);

[alexcrichton]

I'm going to close this in favor of #266 as I'm trying to consolidate all of these various issues about the same problem.