I was not sure what <u32 as NativeWasmType>::Abi should be, so I left it as Self (link). If it should always be the same as the WASM_TYPE, then it probably wouldn't need to be 2 separate lines of code.

But if needs to be i32 to match the WASM_TYPE, I can of course change it. Also, I was not sure how to test it, I did some manual testing, but my I was having some problems with wasm-bindgen, so I couldn't test it as thoroughly as I wanted. Is there an automated testing strategy for something like this? The test would probably need to run in the browser, not sure how that would work.

I see the PR approved, but after some more testing, I found many things wrong when passing around big u64 values and even big i64 values. I will have to re-check everything and create a minimal reproducible example, but it seems that the BigInt conversion is not working correctly.

This is the part where it goes wrong. I think this was added when I wanted to pass u64 values around for fp-bindgen a few months back, but it doesn't seem to work so well with very large values like u64::MAX - 5 for example.

Ok, I have prepared a PR to fix a bug about returning negative i32 values from a module on the web, see #3796.

I think this should wait until that is finished.

@syrusakbary It seems that this has been already implemented on master in the meantime. See api/src/native_type.rs and types/src/lib.rs. I have only added a test to be sure it stays working.