wasm-pack + serde + AtomicUsize

[gakonst]

Serialize is not implemented for AtomicUsize in wasm when using wasm-pack.

Example:

1. Install wasm-pack: curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh

2. Add to your Cargo.toml:

[lib]
crate-type = ["cdylib", "lib"]

[dependencies]
serde = { version = "1.0.106", features = ["derive"] }
wasm-bindgen = "0.2.60"

3. Code:

use std::sync::atomic::AtomicUsize;
use serde::Serialize;

#[derive(Serialize)]
pub struct S(AtomicUsize);

4. Run wasm-pack build (wasm-pack builds into wasm32-unknown-unknown)

It errors with:

pub struct S(AtomicUsize);
  |              ^^^^^^^^^^^ the trait `_IMPL_SERIALIZE_FOR_S::_serde::Serialize` is not implemented for `std::sync::atomic::AtomicUsize

Could anybody explain to me why/if it is not fundamentally impossible to implement this?

[dtolnay]

This looks like a consequence of #1581. Determining exactly which targets can handle which atomic operations is complicated so we've only started with a conservative set and would need to expand as use cases come up.

[gakonst]

@dtolnay thank you for the quick response, your approach makes sense. It seems like wasm32-unknown-unknown has support for Atomics since rust-lang/rust#54017?

[dtolnay]

Sounds good; someone should send a PR to enable the atomic impls on wasm32-unknown-unknown on the correct range of compiler versions.

[dtolnay]

Fixed in serde 1.0.150 by #2337.