Rust/C++ Interop

[benwis]

If I have a Rust project with C/C++ bindings, say treesitter and its parsers, and try to compile that together with cc to Webassembly with wasm32-unknown-unknown, will the ABI issues mentioned here cause errors between the two?
https://github.com/rust-lang/lang-team/blob/master/design-meeting-minutes/2021-04-21-wasm-abi.md

I've found plenty of references to it:
WebAssembly/tool-conventions#88 (comment)
rust-lang/rust#63626
https://github.com/rust-lang/rust/blob/2da942f32802c8233a09744024dfbc34431adf65/src/librustc_target/abi/call/mod.rs#L570-L572
rust-lang/rust#71871
https://github.com/rust-lang/rust/blob/9ab0749ce3fe33fdf84ac2f5b6c6e56b78dc10e8/compiler/rustc_target/src/spec/wasm32_unknown_unknown.rs#L20-L28

I'm trying to understand the problem space. Is it common/prevalent/limited to certain situations? Does it only matter if I compile something Rust to wasm32-wasi or something C to emscripten and then call it from Rust compiled to Webassembly?

[daxpedda]

The issue arises when

If I have a Rust project with C/C++ bindings, say treesitter and its parsers, and try to compile that together with cc to Webassembly with wasm32-unknown-unknown, will the ABI issues mentioned here cause errors between the two?

Yes, because whatever compiler cc is going to use is probably spec compliant, unlike Rustc.

I'm trying to understand the problem space. Is it common/prevalent/limited to certain situations?

rust-lang/rust#71871 explains it quite well, if you manage to avoid calling/linking or fix functions with this kind of ABI incompatibility, you can get away with it.

Does it only matter if I compile something Rust to wasm32-wasi or something C to emscripten and then call it from Rust compiled to Webassembly?

Only Rustc targeting wasm32-unknown-unknown will produce non-spec-compliant ABI, as long as that is in the mix the issue might arise.

[benwis]

Thanks for the confirmation. Crossing my fingers this flag makes it into nightly soon(and wasm-bindgen supports it) to make this possible again: rust-lang/rust#117919

[rafaelbeckel]

@benwis, the flag is now available on nightly, and the latest version of wasm-bindgen should support it. I put together a minimal example, and now I'm closing all the tabs that led me to it with this comment.