return error for unused #[convert]s

1 files changed, 9 insertions, 1 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 785827a..73ae723 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -97,6 +97,7 @@ pub fn dynamize(_attr: TokenStream, input: TokenStream) -> TokenStream {
         assoc_type_conversions: HashMap::new(),
         collections: method_attrs.collections,
         type_conversions: method_attrs.type_conversions,
+        used_conversions: Default::default(),
     };
 
     for item in &original_trait.items {
@@ -127,7 +128,7 @@ pub fn dynamize(_attr: TokenStream, input: TokenStream) -> TokenStream {
         if let TraitItem::Method(method) = item {
             let mut signature = method.sig.clone();
 
-            match convert_trait_signature(&mut signature, &type_converter) {
+            match convert_trait_signature(&mut signature, &mut type_converter) {
                 Ok(parsed_method) => objectifiable_methods.push((signature, parsed_method)),
                 Err((span, err)) => match err {
                     MethodError::NonDispatchableMethod => continue,
@@ -181,6 +182,13 @@ pub fn dynamize(_attr: TokenStream, input: TokenStream) -> TokenStream {
         }
     }
 
+    for ty in type_converter.type_conversions.keys() {
+        if !type_converter.used_conversions.contains(ty) {
+            // FUTURE: relax to warning once proc_macro::Diagnostic is stable
+            return abort!(ty.span(), "unused conversion");
+        }
+    }
+
     let mut method_impls: Vec<ImplItemMethod> = Vec::new();
 
     let mut dyn_trait = ItemTrait {