WebAssembly FFI uses extern "C"

[sdroege]

While reading https://hacks.mozilla.org/2018/01/oxidizing-source-maps-with-rust-and-webassembly/ I noticed the following

it is marked extern "C" so that it is publicly exported in the final .wasm file.

Shouldn't this be extern "WASM" or similar? The FFI interface is not the C one, but the WebAssembly one (or JavaScript?)

[fitzgen]

Discussion is also happening over at rustwasm/team#29

[alexcrichton]

This is now unlikely to change at this point, so I'm going to close this. We've chosen "C" for compatibility with mixing C/Rust in the same module.

[webmaster128]

Does this imply that a Wasm import cannot use multiple return values? Or is this a to-be-silenced linter issue?

---

What I try to do is

extern {
    fn db_next(iterator_id: u32) -> (u32, u32);
}

which gets formatted to

extern "C" {
    fn db_next(iterator_id: u32) -> (u32, u32);
}

which clippy complains about:

warning: `extern` block uses type `(u32, u32)`, which is not FFI-safe
  --> packages/std/src/imports.rs:43:37
   |
43 |     fn db_next(iterator_id: u32) -> (u32, u32);
   |                                     ^^^^^^^^^^ not FFI-safe
   |
   = note: `#[warn(improper_ctypes)]` on by default
   = help: consider using a struct instead
   = note: tuples have unspecified layout