Recent build failures from wasm-bindgen ecosystem

[code-ape]

Describe the Bug

Our CI started randomly failing today on wasm-bindgen projects with no dependency changes. This appears to be a failure with the wasm-bindgen macro. Since our project was a library we didn't have a pinned Cargo.lock I suspect this isn't the fault of wasm-bindgen but of one of its dependencies, but I wasn't sure were else to report it.

UPDATE: We just found that forcing rollback of syn from 1.0.66 to 1.0.65 appears to fix this issue. cargo update -p syn --precise 1.0.65. Leaving this open for wasm-bindgen to do with as they see fit.

Steps to Reproduce

Attempt to run cargo check on urbdyn/petgraph-wasm, commit c4e3db9 with syn version 1.0.66.

Expected Behavior

cargo check exits fine.

Actual Behavior

Recieve hundreds of errors relating to #[wasm_bindgen(...)] and WebAssembly when attempting to build dependency js-sys-0.3.49 in cargo check process.

Additional Context

Last successful build was ~5 hours prior to time of filing this issue. No changes to source code since then. Blowing away my local Cargo.lock duplicated the issue. Sadly I failed to back it up before hand to diff with new one.

Link to last successful build for time reference: https://github.com/urbdyn/petgraph-wasm/actions/runs/696142253

Example from GitHub Actions output, full run viewable at: https://github.com/urbdyn/petgraph-wasm/pull/12/checks?check_run_id=2215306539#step:5:68

# Omitting non-wasm-bindgen related libraries.
Compiling wasm-bindgen-shared v0.2.72
Compiling serde_derive v1.0.125
Compiling serde v1.0.125
Compiling serde_json v1.0.64
Compiling wasm-bindgen v0.2.72
Compiling wasm-bindgen-test-macro v0.3.22
Compiling wasm-bindgen-backend v0.2.72
Compiling wasm-bindgen-macro-support v0.2.72
Compiling wasm-bindgen-macro v0.2.72
Checking js-sys v0.3.49
Checking console_error_panic_hook v0.1.6

error: expected `,`
Error:    --> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/js-sys-0.3.49/src/lib.rs:639:39
    |
639 |         #[wasm_bindgen(js_namespace = Atomics, catch)]
    |                                       ^^^^^^^

error: expected `,`
Error:    --> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/js-sys-0.3.49/src/lib.rs:649:39
    |
649 |         #[wasm_bindgen(js_namespace = Atomics, catch)]
    |                                       ^^^^^^^

[afilini]

I opened this issue in the syn repo before noticing this thread. I believe in a way this bug is actually here in wasm-bindgen, but nobody had noticed it before because syn also had a different "bug", or at least it was behaving differently when trying to parse an ExprArray which was not an ExprArray (it was still consuming tokens from the parse buffer).

I guess the fix here would be to just avoid forking the ParseBuffer?

wasm-bindgen/crates/macro-support/src/parser.rs

Line 302 in 0cec406

let input_before_parse = input.fork();