Stream: wit-bindgen

Topic: ✔ wit_bindgen::generate! throws errors after upgrade

Christoph Brewing (Oct 04 2023 at 12:29):

I had a running real-world application based on Rust/WASM. Let's call it a decoder. Before I fell into the black (summer) hole, everything was fine, compiling, executing ...

I was working on wasmtime = { version = "10", features = ["component-model"] } and wit-bindgen = "0.9".

Now, after an upgrade to wasmtime = { version = "13", features = ["component-model"] } and wit-bindgen = "0.12" I get compilation errors. My world.wit looks like

package decoder:api

interface decode {
  [..]
}

world decoder {
  export decode
}

I try to use it like

use crate::exports::decoder::api::decode::*;
// [..]
wit_bindgen::generate!(in "wit/world.wit");
// [..]
struct Decoder;
export_decoder!(Decoder);

The errors are

error: no `exports` map provided in configuration but key is required for `decoder:api/decode`
  --> src/lib.rs:25:1
   |
25 | wit_bindgen::generate!(in "wit/world.wit");
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in the macro `wit_bindgen::generate` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0433]: failed to resolve: could not find `exports` in the crate root
  --> src/lib.rs:23:12
   |
23 | use crate::exports::decoder::api::decode::{DecodeReturn, SignalHandle};
   |            ^^^^^^^ could not find `exports` in the crate root

error: cannot find macro `export_decoder` in this scope
  --> src/lib.rs:47:1
   |
47 | export_decoder!(Decoder);
   | ^^^^^^^^^^^^^^

error[E0433]: failed to resolve: could not find `exports` in the crate root
  --> src/lib.rs:59:13
   |
59 | impl crate::exports::decoder::api::decode::Decode for Decoder {
   |             ^^^^^^^ could not find `exports` in the crate root

I guess, it does not take much to get it compiling again. However, I do not understand what to change.
Also, in order to avoid this kind of question in the future, is there any place I can have a look in the docs?

Thanks a lot for any hint!

Alex Crichton (Oct 04 2023 at 14:27):

The syntax for generate! has changed in the meantime. It looks like the errors you're seeing are from a Rust guest compiled to WebAssembly, so I'd recommending looking at the documentation for Rust support for more guidance

Christoph Brewing (Oct 04 2023 at 19:37):

So I tried the first two examples after having installed cargo component:

1. Building a Component with cargo component
2. Exporting an interface with cargo component

The first compiles as described. The second one is more relevant for me since me too, I try to export an interface. However, it yields the following error:

$ cargo component build --release
    Encoding target for add (add/target/bindings/add/target.wasm)
   Compiling add v0.1.0 add)
error[E0432]: unresolved import `super`
 --> src/lib.rs:3:1
  |
3 | cargo_component_bindings::generate!();
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no `Component` in the root
  |
  = note: this error originates in the macro `cargo_component_bindings::generate` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider importing this enum instead
  |
3 | std::path::Component as _GuestImpl;
  | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

For the second example I have reused the project from the first example, just replaced world.wit and lib.rs.
Is it meant to work this way?

Brian (Oct 04 2023 at 19:43):

@Christoph Brewing cargo_component_bindings::generate! assumes the implementation to be at super::Component (relative to bindings module generated by the macro). However, you can override it using the implementor argument to the macro; see https://github.com/bytecodealliance/cargo-component/issues/149 for an example!

Christoph Brewing (Oct 05 2023 at 08:19):

Thanks! The combination of hints made it work for me.

Notification Bot (Oct 05 2023 at 08:19):

Christoph Brewing has marked this topic as resolved.

Last updated: Nov 22 2024 at 17:03 UTC