WebAssembly FFI uses extern "C" #47599

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1. fitzgen commented on Jan 19, 2018

   

   fitzgen

   on Jan 19, 2018

   Member

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   Discussion is also happening over at rustwasm/team#29
2. emilyalbini

   added

   C-enhancementCategory: An issue proposing an enhancement or a PR with one.Category: An issue proposing an enhancement or a PR with one.

   A-FFIArea: Foreign function interface (FFI)Area: Foreign function interface (FFI)

   O-wasmTarget: WASM (WebAssembly), http://webassembly.org/Target: WASM (WebAssembly), http://webassembly.org/

   on Jan 21, 2018
3. alexcrichton commented on Dec 16, 2019

   

   alexcrichton

   on Dec 16, 2019

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   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.
4. alexcrichton

   closed this as completedon Dec 16, 2019
5. webmaster128 commented on Oct 27, 2020

   

   webmaster128

   on Oct 27, 2020

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   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