Error compiling to wasm index out of bounds when implementing IntoWasmAbi

[dgkf]

Describe the Bug

Introducing implementations of WasmDescribe, IntoWasmAbi and FromWasmAbi cause builds to fail with error:

[INFO]: 🎯  Checking for the Wasm target...
[INFO]: 🌀  Compiling to Wasm...
   Compiling test-wasm-bindgen v0.1.0 (~/Projects/Programming/test-wasm-binding)
    Finished release [optimized] target(s) in 0.10s
thread 'main' panicked at 'index out of bounds: the len is 0 but the index is 0', ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wasm-bindgen-cli-support-0.2.87/src/descriptor.rs:218:15

Steps to Reproduce

1. Create a simple rust lib crate (I used the hello-world example as a basis)
2. Introduce a return type that requires an implementation of IntoWasmAbi/FromWasmAbi
3. Attempt to build
4. Observe error

see this repo with the code used to minimally produce the bug

Expected Behavior

The build succeeds

Actual Behavior

The build fails with an index out of bounds error

Additional Context

This seems to have popped up from time to time in wasm-bindgen's history with,
seemingly resolved by matching dependency versions (#3441, #2776, among others).

Troubleshooting

• Build error only arises when IntoWasmAbi/FromWasmAbi are implemented for a new type.
• As far as I can tell, dependency versions are all the same. I've tried many
  of the older versions that resolved previous issues to no avail (0.2.78, 0.2.79, 0.2.84).
• Attempted reinstalling wasm-pack with wasm-pack --locked to no avail

[dgkf]

I'm realizing that perhaps the intention is not to be able to define arbitrary types, but to coerce a type into one of the already provided WasmAbi options. I had sort of hoped that wasm-bindgen would do some magic for simple structs, but I'm not seeing evidence of it in the docs.

I was loosely trying to follow this example, and I'm not sure if I misunderstood the struct here to be an example when instead it is just meant to show a special case. If the latter, feel free to close as user error.

[daxpedda]

I'm realizing that perhaps the intention is not to be able to define arbitrary types, but to coerce a type into one of the already provided WasmAbi options.

Pretty much, in your minimal example you didn't add a description to WasmDescribe, so this can't really work. But all of this is subject to the ABI implemented by wasm-bindgen which you can't really expand.