Turn off syn/clone-impls feature

Cargo.toml

@@ -18,7 +18,7 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0.74"
 quote = "1.0.35"
-syn = { version = "2.0.46", default-features = false, features = ["full", "visit-mut", "parsing", "printing", "proc-macro", "clone-impls"] }
+syn = { version = "2.0.46", default-features = false, features = ["full", "visit-mut", "parsing", "printing", "proc-macro"] }
 
 [dev-dependencies]
 futures = "0.3.30"

src/expand.rs

@@ -169,8 +169,8 @@ fn transform_sig(
     sig.fn_token.span = sig.asyncness.take().unwrap().span;
 
     let (ret_arrow, ret) = match &sig.output {
-        ReturnType::Default => (Token![->](Span::call_site()), quote!(())),
-        ReturnType::Type(arrow, ret) => (*arrow, quote!(#ret)),
+        ReturnType::Default => (quote!(->), quote!(())),
+        ReturnType::Type(arrow, ret) => (quote!(#arrow), quote!(#ret)),
     };
 
     let mut lifetimes = CollectLifetimes::new();

src/lifetime.rs

@@ -19,7 +19,7 @@ impl CollectLifetimes {
         }
     }
 
-    fn visit_opt_lifetime(&mut self, reference: Token![&], lifetime: &mut Option<Lifetime>) {
+    fn visit_opt_lifetime(&mut self, reference: &Token![&], lifetime: &mut Option<Lifetime>) {
         match lifetime {
             None => *lifetime = Some(self.next_lifetime(reference.span)),
             Some(lifetime) => self.visit_lifetime(lifetime),
@@ -45,14 +45,14 @@ impl CollectLifetimes {
 impl VisitMut for CollectLifetimes {
     fn visit_receiver_mut(&mut self, arg: &mut Receiver) {
         if let Some((reference, lifetime)) = &mut arg.reference {
-            self.visit_opt_lifetime(*reference, lifetime);
+            self.visit_opt_lifetime(reference, lifetime);
         } else {
             visit_mut::visit_type_mut(self, &mut arg.ty);
         }
     }
 
     fn visit_type_reference_mut(&mut self, ty: &mut TypeReference) {
-        self.visit_opt_lifetime(ty.and_token, &mut ty.lifetime);
+        self.visit_opt_lifetime(&ty.and_token, &mut ty.lifetime);
         visit_mut::visit_type_reference_mut(self, ty);
     }
 

src/receiver.rs

@@ -42,8 +42,8 @@ struct HasMutPat(Option<Token![mut]>);
 
 impl VisitMut for HasMutPat {
     fn visit_pat_ident_mut(&mut self, i: &mut PatIdent) {
-        if let Some(m) = i.mutability {
-            self.0 = Some(m);
+        if let Some(m) = &i.mutability {
+            self.0 = Some(Token![mut](m.span));
         } else {
             visit_mut::visit_pat_ident_mut(self, i);
         }