Fix usage with impl trait returning functions

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "culpa"
-version = "1.0.0"
+version = "1.0.1"
 edition = "2018"
 license = "MIT OR Apache-2.0"
 
@@ -10,6 +10,6 @@ keywords = ["error-handling", "exceptions"]
 
 [dependencies.culpa-macros]
 path = "macros"
-version = "=1.0.0"
+version = "=1.0.1"
 
 [workspace]

macros/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "culpa-macros"
-version = "1.0.0"
+version = "1.0.1"
 edition = "2018"
 license = "MIT OR Apache-2.0"
 

macros/src/throws.rs

@@ -13,15 +13,15 @@ use crate::Args;
 pub struct Throws {
     args: Args,
     outer_fn: bool,
-    return_type: Box<syn::Type>,
+    return_type: syn::Type,
 }
 
 impl Throws {
     pub fn new(args: Args) -> Throws {
         Throws {
             args,
             outer_fn: true,
-            return_type: Box::new(syn::parse_quote!(())),
+            return_type: syn::parse_quote!(()),
         }
     }
 
@@ -112,7 +112,16 @@ impl Fold for Throws {
         }
         let return_type = self.args.ret(i);
         let syn::ReturnType::Type(_, ty) = &return_type else { unreachable!() };
-        self.return_type = ty.clone();
+        struct ImplTraitToInfer;
+        impl Fold for ImplTraitToInfer {
+            fn fold_type(&mut self, i: syn::Type) -> syn::Type {
+                match i {
+                    syn::Type::ImplTrait(_) => syn::Type::Infer(syn::parse_quote!(_)),
+                    i => syn::fold::fold_type(self, i),
+                }
+            }
+        }
+        self.return_type = ImplTraitToInfer.fold_type(ty.as_ref().clone());
         return_type
     }
 

tests/throws.rs

@@ -135,6 +135,9 @@ pub fn let_else(a: Option<u8>) -> u8 {
     a
 }
 
+#[throws]
+pub fn impl_trait() -> impl std::fmt::Debug {}
+
 #[throws(i32)]
 #[deny(unreachable_code)]
 pub fn unreachable() {