From c69d605b7dc6a67824778f518c4439304b0a9241 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Thu, 2 Jun 2022 15:14:32 -0700
Subject: [PATCH 1/2] Add regression test of issue 204

---
 tests/test.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tests/test.rs b/tests/test.rs
index 87897b1..6859639 100644
--- a/tests/test.rs
+++ b/tests/test.rs
@@ -1439,3 +1439,13 @@ pub mod issue199 {
         assert_eq!(counter.get(), 1);
     }
 }
+
+// https://github.com/dtolnay/async-trait/issues/204
+pub mod issue204 {
+    use async_trait::async_trait;
+
+    #[async_trait]
+    pub trait Trait {
+        async fn f(arg: &impl Trait);
+    }
+}

From 91401c823b6362ce137fa01739cc67d5a20221a3 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Thu, 2 Jun 2022 15:18:09 -0700
Subject: [PATCH 2/2] Use parentheses to disambiguate impl Trait

---
 src/lifetime.rs | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/lifetime.rs b/src/lifetime.rs
index d8e8d88..7ceda4f 100644
--- a/src/lifetime.rs
+++ b/src/lifetime.rs
@@ -1,7 +1,9 @@
-use proc_macro2::Span;
+use proc_macro2::{Span, TokenStream};
+use std::mem;
 use syn::visit_mut::{self, VisitMut};
 use syn::{
-    parse_quote_spanned, Expr, GenericArgument, Lifetime, Receiver, TypeImplTrait, TypeReference,
+    parse_quote_spanned, token, Expr, GenericArgument, Lifetime, Receiver, Type, TypeImplTrait,
+    TypeParen, TypeReference,
 };
 
 pub struct CollectLifetimes {
@@ -78,6 +80,17 @@ impl VisitMut for AddLifetimeToImplTrait {
         visit_mut::visit_type_impl_trait_mut(self, ty);
     }
 
+    fn visit_type_reference_mut(&mut self, ty: &mut TypeReference) {
+        if let Type::ImplTrait(_) = *ty.elem {
+            let elem = mem::replace(&mut *ty.elem, Type::Verbatim(TokenStream::new()));
+            *ty.elem = Type::Paren(TypeParen {
+                paren_token: token::Paren(ty.and_token.span),
+                elem: Box::new(elem),
+            });
+        }
+        visit_mut::visit_type_reference_mut(self, ty);
+    }
+
     fn visit_expr_mut(&mut self, _e: &mut Expr) {
         // Do not recurse into impl Traits inside of an array length expression.
         //