return error for unused #[convert]s

5 files changed, 51 insertions, 22 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 {
diff --git a/src/trait_sig.rs b/src/trait_sig.rs
index a1be44f..ce6f318 100644
--- a/src/trait_sig.rs
+++ b/src/trait_sig.rs
@@ -57,7 +57,7 @@ pub struct SignatureChanges {
 
 pub fn convert_trait_signature(
     signature: &mut Signature,
-    type_converter: &TypeConverter,
+    type_converter: &mut TypeConverter,
 ) -> Result<SignatureChanges, (Span, MethodError)> {
     if is_non_dispatchable(signature) {
         return Err((signature.span(), MethodError::NonDispatchableMethod));
@@ -144,7 +144,7 @@ fn bounds_self_and_has_bound_sized(predicate: &WherePredicate) -> bool {
 
 #[cfg(test)]
 mod tests {
-    use std::collections::HashMap;
+    use std::collections::{HashMap, HashSet};
 
     use quote::{format_ident, quote};
     use syn::{TraitItemMethod, Type};
@@ -161,6 +161,7 @@ mod tests {
             collections: HashMap::new(),
             trait_ident: format_ident!("test"),
             type_conversions: HashMap::new(),
+            used_conversions: HashSet::new(),
         }
     }
 
@@ -172,7 +173,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Ok(SignatureChanges {
                 return_type: TypeTransform::NoOp,
                 ..
@@ -194,7 +195,7 @@ mod tests {
         type_converter.assoc_type_conversions.insert(ident, dest);
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &type_converter),
+            convert_trait_signature(&mut type1.sig, &mut type_converter),
             Ok(SignatureChanges {
                 return_type: TypeTransform::Into,
                 ..
@@ -210,7 +211,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((
                 _,
                 MethodError::Transform(TransformError::AssocTypeWithoutDestType)
@@ -226,7 +227,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::NonDispatchableMethod))
         ));
     }
@@ -239,7 +240,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::NonDispatchableMethod))
         ));
     }
@@ -252,7 +253,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::NonDispatchableMethod))
         ));
     }
@@ -265,7 +266,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::NonDispatchableMethod))
         ));
     }
@@ -278,7 +279,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::Transform(TransformError::UnsupportedType)))
         ));
     }
@@ -291,7 +292,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::Transform(TransformError::UnsupportedType)))
         ));
     }
@@ -304,7 +305,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::Transform(TransformError::UnsupportedType)))
         ));
     }
@@ -317,7 +318,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::Transform(TransformError::UnsupportedType)))
         ));
     }
@@ -330,7 +331,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::AssocTypeInInputs))
         ));
     }
@@ -343,7 +344,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::AssocTypeInInputs))
         ));
     }
@@ -356,7 +357,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::ImplTraitInInputs))
         ));
     }
@@ -369,7 +370,7 @@ mod tests {
         .unwrap();
 
         assert!(matches!(
-            convert_trait_signature(&mut type1.sig, &test_converter()),
+            convert_trait_signature(&mut type1.sig, &mut test_converter()),
             Err((_, MethodError::Transform(TransformError::UnsupportedType)))
         ));
     }
diff --git a/src/transform.rs b/src/transform.rs
index ae345c8..c56bec1 100644
--- a/src/transform.rs
+++ b/src/transform.rs
@@ -1,4 +1,7 @@
-use std::{collections::HashMap, rc::Rc};
+use std::{
+    collections::{HashMap, HashSet},
+    rc::Rc,
+};
 
 use proc_macro2::Span;
 use quote::quote;
@@ -20,6 +23,7 @@ pub struct TypeConverter {
     pub collections: HashMap<Ident, usize>,
     pub trait_ident: Ident,
     pub type_conversions: HashMap<Type, Rc<Convert>>,
+    pub used_conversions: HashSet<Type>,
 }
 
 #[derive(Debug)]
@@ -60,8 +64,12 @@ impl TypeConverter {
         None
     }
 
-    pub fn convert_type(&self, type_: &mut Type) -> Result<TypeTransform, (Span, TransformError)> {
+    pub fn convert_type(
+        &mut self,
+        type_: &mut Type,
+    ) -> Result<TypeTransform, (Span, TransformError)> {
         if let Some(conv) = self.type_conversions.get(type_) {
+            self.used_conversions.insert(conv.original_type.clone());
             *type_ = conv.dest_type.clone();
             return Ok(TypeTransform::Verbatim(conv.clone()));
         }
@@ -223,7 +231,7 @@ impl TypeConverter {
 
 pub fn dynamize_function_bounds(
     generics: &mut Generics,
-    type_converter: &TypeConverter,
+    type_converter: &mut TypeConverter,
 ) -> Result<HashMap<Ident, Vec<TypeTransform>>, (Span, MethodError)> {
     let mut type_param_transforms = HashMap::new();
 
@@ -285,7 +293,7 @@ pub fn dynamize_function_bounds(
 
 fn dynamize_trait_bound(
     bound: &mut TraitBound,
-    type_converter: &TypeConverter,
+    type_converter: &mut TypeConverter,
     type_ident: &Ident,
     type_param_transforms: &mut HashMap<Ident, Vec<TypeTransform>>,
 ) -> Result<(), (Span, MethodError)> {
diff --git a/ui-tests/src/bin/attr_convert_unused.rs b/ui-tests/src/bin/attr_convert_unused.rs
new file mode 100644
index 0000000..b7ee474
--- /dev/null
+++ b/ui-tests/src/bin/attr_convert_unused.rs
@@ -0,0 +1,7 @@
+#[dynamize::dynamize]
+#[convert = |x: Foo| -> Bar {x.baz()}]
+trait Trait {
+    fn test(&self);
+}
+
+fn main() {}
diff --git a/ui-tests/src/bin/attr_convert_unused.stderr b/ui-tests/src/bin/attr_convert_unused.stderr
new file mode 100644
index 0000000..e715236
--- /dev/null
+++ b/ui-tests/src/bin/attr_convert_unused.stderr
@@ -0,0 +1,5 @@
+error: unused conversion
+ --> src/bin/attr_convert_unused.rs:2:17
+  |
+2 | #[convert = |x: Foo| -> Bar {x.baz()}]
+  |                 ^^^