Insert AsyncTrait parameter prior to const parameters

Author: taiki-e

src/expand.rs

@@ -414,10 +414,22 @@ fn transform_block(
             if !is_local {
                 self_param.bounds.extend(self_bound);
             }
+            let count = standalone
+                .generics
+                .params
+                .iter()
+                .take_while(|param| {
+                    if let GenericParam::Const(_) = param {
+                        false
+                    } else {
+                        true
+                    }
+                })
+                .count();
             standalone
                 .generics
                 .params
-                .push(GenericParam::Type(self_param));
+                .insert(count, GenericParam::Type(self_param));
             types.push(Ident::new("Self", Span::call_site()));
         }
     }

src/lib.rs

@@ -303,6 +303,8 @@
 //! let object = &value as &dyn ObjectSafe;
 //! ```
 
+#![allow(clippy::match_like_matches_macro)] // matches! requires Rust 1.42
+
 extern crate proc_macro;
 
 mod args;

tests/test.rs

@@ -1,4 +1,7 @@
-#![cfg_attr(async_trait_nightly_testing, feature(specialization, const_generics))]
+#![cfg_attr(
+    async_trait_nightly_testing,
+    feature(min_specialization, min_const_generics)
+)]
 
 use async_trait::async_trait;
 
@@ -1048,3 +1051,29 @@ pub mod issue129 {
         }
     }
 }
+
+// https://github.com/dtolnay/async-trait/issues/134
+#[cfg(async_trait_nightly_testing)]
+pub mod issue134 {
+    use async_trait::async_trait;
+
+    #[async_trait]
+    trait TestTrait {
+        async fn run<const DUMMY: bool>(self) -> ()
+        where
+            Self: Sized,
+        {
+        }
+    }
+
+    pub struct TestStruct;
+
+    #[async_trait]
+    impl TestTrait for TestStruct {
+        async fn run<const DUMMY: bool>(self) -> ()
+        where
+            Self: Sized,
+        {
+        }
+    }
+}