wiggle::async_trait is defined as async_trait::async_trait(?Send)

async methods used by wiggle currently need to Not have the Send
constraint, so rather than make all use sites pass the argument
to the re-exported async_trait macro, define a new macro that
applies the argument.

Cargo.lock

@@ -3651,6 +3651,7 @@ dependencies = [
 name = "wiggle-macro"
 version = "0.25.0"
 dependencies = [
+ "proc-macro2",
  "quote",
  "syn",
  "wiggle",

crates/wiggle/generate/src/module_trait.rs

@@ -89,8 +89,7 @@ pub fn define_module_trait(names: &Names, m: &Module, settings: &CodegenSettings
     });
 
     quote! {
-        use #rt::async_trait;
+        #[#rt::async_trait]
-        #[async_trait(?Send)]
         pub trait #traitname {
             #(#traitmethods)*
         }

crates/wiggle/macro/Cargo.toml

@@ -25,6 +25,7 @@ wiggle-generate = { path = "../generate", version = "0.25.0" }
 witx = { version = "0.9.0", path = "../../wasi-common/WASI/tools/witx" }
 quote = "1.0"
 syn = { version = "1.0", features = ["full"] }
+proc-macro2 = "1.0"
 
 [dev-dependencies]
 wiggle = { path = ".." }

crates/wiggle/macro/src/lib.rs

@@ -83,11 +83,12 @@ use syn::parse_macro_input;
 ///
 /// /// The above witx text contains one module called `$example`. So, we must
 /// /// implement this one method trait for our ctx type.
-/// #[wiggle::async_trait(?Send)]
+/// #[wiggle::async_trait]
 /// /// We specified in the `async_` field that `example::double_int_return_float`
 /// /// is an asynchronous method. Therefore, we use the `async_trait` proc macro
-/// /// (re-exported by wiggle from the crate of the same name) to define this
+/// /// to define this trait, so that `double_int_return_float` can be an `async fn`.
-/// /// trait, so that `double_int_return_float` can be an `async fn`.
+/// /// `wiggle::async_trait` is defined as `#[async_trait::async_trait(?Send)]` -
+/// /// in wiggle, async methods do not have the Send constaint.
 /// impl example::Example for YourCtxType {
 ///     /// The arrays module has two methods, shown here.
 ///     /// Note that the `GuestPtr` type comes from `wiggle`,
@@ -156,3 +157,13 @@ pub fn from_witx(args: TokenStream) -> TokenStream {
 
     TokenStream::from(quote! { #code #metadata })
 }
+
+#[proc_macro_attribute]
+pub fn async_trait(attr: TokenStream, item: TokenStream) -> TokenStream {
+    let _ = parse_macro_input!(attr as syn::parse::Nothing);
+    let item = proc_macro2::TokenStream::from(item);
+    TokenStream::from(quote! {
+        #[wiggle::async_trait_crate::async_trait(?Send)]
+        #item
+    })
+}

crates/wiggle/src/lib.rs

@@ -6,9 +6,8 @@ use std::slice;
 use std::str;
 use std::sync::Arc;
 
-pub use wiggle_macro::from_witx;
+pub use wiggle_macro::{async_trait, from_witx};
-// re-exports so users of wiggle don't need to track the dependency:
+
-pub use async_trait::async_trait;
 pub use bitflags;
 
 #[cfg(feature = "wiggle_metadata")]
@@ -24,6 +23,10 @@ pub use error::GuestError;
 pub use guest_type::{GuestErrorType, GuestType, GuestTypeTransparent};
 pub use region::Region;
 
+pub mod async_trait_crate {
+    pub use async_trait::*;
+}
+
 /// A trait which abstracts how to get at the region of host memory taht
 /// contains guest memory.
 ///

crates/wiggle/tests/atoms_async.rs

@@ -14,7 +14,7 @@ wiggle::from_witx!({
 
 impl_errno!(types::Errno);
 
-#[wiggle::async_trait(?Send)]
+#[wiggle::async_trait]
 impl<'a> atoms::Atoms for WasiCtx<'a> {
     async fn int_float_args(&self, an_int: u32, an_float: f32) -> Result<(), types::Errno> {
         println!("INT FLOAT ARGS: {} {}", an_int, an_float);

crates/wiggle/wasmtime/tests/atoms_async.rs

@@ -28,7 +28,7 @@ impl wiggle::GuestErrorType for types::Errno {
     }
 }
 
-#[wasmtime_wiggle::async_trait(?Send)]
+#[wasmtime_wiggle::async_trait]
 impl atoms::Atoms for Ctx {
     fn int_float_args(&self, an_int: u32, an_float: f32) -> Result<(), types::Errno> {
         println!("INT FLOAT ARGS: {} {}", an_int, an_float);