allow(async_fn_in_trait) on traits with Send variant

Author: tmandry

trait-variant/examples/variant.rs

@@ -10,8 +10,8 @@ use std::future::Future;
 
 use trait_variant::make_variant;
 
-#[make_variant(SendIntFactory: Send)]
-trait IntFactory {
+#[make_variant(IntFactory: Send)]
+pub trait LocalIntFactory {
     const NAME: &'static str;
 
     type MyFut<'a>: Future
@@ -24,4 +24,11 @@ trait IntFactory {
     fn another_async(&self, input: Result<(), &str>) -> Self::MyFut<'_>;
 }
 
+#[allow(dead_code)]
+fn spawn_task(factory: impl IntFactory + 'static) {
+    tokio::spawn(async move {
+        let _int = factory.make(1, "foo").await;
+    });
+}
+
 fn main() {}

trait-variant/src/variant.rs

@@ -56,15 +56,29 @@ pub fn make_variant(
     let attrs = parse_macro_input!(attr as Attrs);
     let item = parse_macro_input!(item as ItemTrait);
 
+    let maybe_allow_async_lint = if attrs
+        .variant
+        .bounds
+        .iter()
+        .any(|b| b.path.segments.last().unwrap().ident.to_string() == "Send")
+    {
+        quote! { #[allow(async_fn_in_trait)] }
+    } else {
+        quote! {}
+    };
+
     let variant = mk_variant(&attrs, &item);
     let blanket_impl = mk_blanket_impl(&attrs, &item);
-    let output = quote! {
+
+    quote! {
+        #maybe_allow_async_lint
         #item
+
         #variant
-        #blanket_impl
-    };
 
-    output.into()
+        #blanket_impl
+    }
+    .into()
 }
 
 fn mk_variant(attrs: &Attrs, tr: &ItemTrait) -> TokenStream {