export\! macro not accessible in rust_wasm_component_bindgen

[avrabe]

Summary

The export\! macro generated by rust_wasm_component_bindgen is not accessible from user code due to visibility restrictions.

Problem Details

1. Generated wrapper creates export\! macro as pub(crate):

// In generated wrapper at line 148:
pub(crate) use __export_camera_front_impl as export;

2. User code cannot access it:

// Error: macro `export` is private
camera_front_ecu_bindings::export\!(Component);

3. Compilation error:

error[E0603]: macro `export` is private
  --> components/sensors/camera-front/src/lib.rs:17:28

Root Cause

The wrapper file at /rust/rust_wasm_component_bindgen.bzl generates the export macro with pub(crate) visibility, but the bindings are compiled as a separate crate, making the macro inaccessible from user code.

Suggested Fix

In the wrapper generation template, change:

pub(crate) use __export_camera_front_impl as export;

to:

pub use __export_camera_front_impl as export;

Steps to Reproduce

1. Create a WIT file with a world definition:

package example:component;

world my-world {
    export process: func() -> string;
}

2. Use rust_wasm_component_bindgen in BUILD.bazel:

rust_wasm_component_bindgen(
    name = "my_component",
    srcs = ["src/lib.rs"],
    wit = ":my_interfaces",
)

3. Try to use the export macro in src/lib.rs:

use my_component_bindings::{Guest, export};

struct Component;

impl Guest for Component {
    fn process() -> String {
        "Hello".to_string()
    }
}

export\!(Component);

4. Build fails with error[E0603]: macro export is private

Impact

This blocks migration of projects using the new rust_wasm_component_bindgen API, as there's no way to export the component implementation.

Environment

• Bazel 8.3.1
• rules_wasm_component commit: 125a46f
• Platform: macOS ARM64

[avrabe]

Fixed in commit 04f2a2d by adding the --pub-export-macro flag to wit-bindgen.

Solution:

• Added --pub-export-macro flag to wit_bindgen.bzl to make the export macro public
• Simplified wrapper generation in rust_wasm_component_bindgen.bzl
• Added comprehensive test suite for export macro visibility

The export! macro is now accessible from separate crates. Test case added in test/export_macro/ verifies the fix works correctly.

[avrabe]

Resolved by implementing proper solution using wit-bindgen's --pub-export-macro flag. The export! macro is now accessible from external crates as expected.

[avrabe]

After the fix, there's now a new issue with macro name conflicts:

error[E0255]: the name `__export_world_camera_front_cabi` is defined multiple times
  --> bazel-out/darwin_arm64-fastbuild-ST-805526428602/bin/components/sensors/camera-front/camera_front_ecu_wrapper.rs:96:9
   |
82 | macro_rules\! __export_world_camera_front_cabi{
   | --------------------------------------------- previous definition of the macro `__export_world_camera_front_cabi` here
...
96 | pub use __export_world_camera_front_cabi;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `__export_world_camera_front_cabi` reimported here

It appears that both the generated bindings and the wrapper are defining the same macro name, causing a conflict. The generated bindings now have #[macro_export] on the __export_world_camera_front_cabi macro (line 32 in the generated file), and the wrapper is also trying to re-export it (line 96).

The wrapper generation should probably check if the macro is already exported and avoid re-exporting it in that case.

[avrabe]

Update: The export! macro visibility issue is resolved - the macro is now accessible from external crates.

However, there's a separate platform targeting issue. The rust_wasm_component_bindgen is trying to build for aarch64-apple-darwin instead of wasm32-wasip2. This is why the build fails with undefined symbols - it's not building for the correct WebAssembly target.

Status:

• ✅ Export macro is now public and accessible
• ❌ Platform targeting issue remains - not building for wasm32-wasip2

Need to investigate the platform transition configuration in rust_wasm_component_bindgen.

[avrabe]

Progress Update:

✅ Export macro visibility FIXED - The export! macro is now accessible from external crates
✅ WASM transition implemented - Added proper platform transition for bindings library

Current Status:

• The export! macro visibility issue is fully resolved
• Added WASM platform transition to ensure bindings are built for the correct target
• Created comprehensive test suite to verify the fix

Remaining Issue:
There's a broader toolchain configuration issue where the Rust toolchain is defaulting to wasm32-wasip1 instead of wasm32-wasip2. This appears to be a configuration issue with the rules_rust toolchain selection, not related to the original export macro problem.

Next Steps:
Need to investigate the toolchain configuration to ensure wasm32-wasip2 is properly selected by the platform transition.