feat: Add generic count check for trait methods

compiler/noirc_frontend/src/hir/def_collector/dc_crate.rs

@@ -996,7 +996,13 @@
         new_resolver.set_self_type(Some(self_type.clone()));
 
         if let Some(trait_id) = maybe_trait_id {
-            check_methods_signatures(&mut new_resolver, &impl_methods, trait_id, errors);
+            check_methods_signatures(
+                &mut new_resolver,
+                &impl_methods,
+                trait_id,
+                trait_impl.generics.len(),
+                errors,
+            );
 
             let resolved_trait_impl = Shared::new(TraitImpl {
                 ident: trait_impl.trait_path.last_segment().clone(),
@@ -1028,11 +1034,12 @@
     methods
 }
 
 // TODO(vitkov): Move this out of here and into type_check
 fn check_methods_signatures(
     resolver: &mut Resolver,
     impl_methods: &Vec<(FileId, FuncId)>,
     trait_id: TraitId,
+    trait_impl_generic_count: usize,
     errors: &mut Vec<(CompilationError, FileId)>,
 ) {
     let the_trait = resolver.interner.get_trait(trait_id);
@@ -1043,24 +1050,42 @@
     let _ = the_trait.self_type_typevar.borrow_mut().bind_to(self_type.clone(), the_trait.span);
 
     for (file_id, func_id) in impl_methods {
-        let meta = resolver.interner.function_meta(func_id);
+        let impl_method = resolver.interner.function_meta(func_id);
         let func_name = resolver.interner.function_name(func_id).to_owned();
 
         let mut typecheck_errors = Vec::new();
 
-        // `method` is None in the case where the impl block has a method that's not part of the trait.
+        // This is None in the case where the impl block has a method that's not part of the trait.
         // If that's the case, a `MethodNotInTrait` error has already been thrown, and we can ignore
         // the impl method, since there's nothing in the trait to match its signature against.
-        if let Some(method) =
+        if let Some(trait_method) =
             the_trait.methods.iter().find(|method| method.name.0.contents == func_name)
         {
-            let function_typ = meta.typ.instantiate(resolver.interner);
+            let impl_function_type = impl_method.typ.instantiate(resolver.interner);
+
+            let impl_method_generic_count =
+                impl_method.typ.generic_count() - trait_impl_generic_count;
+            let trait_method_generic_count = trait_method.generics.len();
+
+            if impl_method_generic_count != trait_method_generic_count {
+                let error = DefCollectorErrorKind::MismatchTraitImplementationNumGenerics {
+                    impl_method_generic_count,
+                    trait_method_generic_count,
+                    trait_name: the_trait.name.to_string(),
+                    method_name: func_name.to_string(),
+                    span: impl_method.location.span,
+                };
+                errors.push((error.into(), *file_id));
+            }
 
-            if let Type::Function(params, _, _) = function_typ.0 {
-                if method.arguments.len() == params.len() {
+            if let Type::Function(impl_params, _, _) = impl_function_type.0 {
+                if trait_method.arguments.len() == impl_params.len() {
                     // Check the parameters of the impl method against the parameters of the trait method
+                    let args = trait_method.arguments.iter();
+                    let args_and_params = args.zip(&impl_params).zip(&impl_method.parameters.0);
+
                     for (parameter_index, ((expected, actual), (hir_pattern, _, _))) in
-                        method.arguments.iter().zip(&params).zip(&meta.parameters.0).enumerate()
+                        args_and_params.enumerate()
                     {
                         expected.unify(actual, &mut typecheck_errors, || {
                             TypeCheckError::TraitMethodParameterTypeMismatch {
@@ -1073,33 +1098,28 @@
                         });
                     }
                 } else {
-                    errors.push((
-                        DefCollectorErrorKind::MismatchTraitImplementationNumParameters {
-                            actual_num_parameters: meta.parameters.0.len(),
-                            expected_num_parameters: method.arguments.len(),
-                            trait_name: the_trait.name.to_string(),
-                            method_name: func_name.to_string(),
-                            span: meta.location.span,
-                        }
-                        .into(),
-                        *file_id,
-                    ));
+                    let error = DefCollectorErrorKind::MismatchTraitImplementationNumParameters {
+                        actual_num_parameters: impl_method.parameters.0.len(),
+                        expected_num_parameters: trait_method.arguments.len(),
+                        trait_name: the_trait.name.to_string(),
+                        method_name: func_name.to_string(),
+                        span: impl_method.location.span,
+                    };
+                    errors.push((error.into(), *file_id));
                 }
             }
 
             // Check that impl method return type matches trait return type:
             let resolved_return_type =
-                resolver.resolve_type(meta.return_type.get_type().into_owned());
+                resolver.resolve_type(impl_method.return_type.get_type().into_owned());
 
-            method.return_type.unify(&resolved_return_type, &mut typecheck_errors, || {
-                let ret_type_span =
-                    meta.return_type.get_type().span.expect("return type must always have a span");
+            trait_method.return_type.unify(&resolved_return_type, &mut typecheck_errors, || {
+                let ret_type_span = impl_method.return_type.get_type().span;
+                let expr_span = ret_type_span.expect("return type must always have a span");
 
-                TypeCheckError::TypeMismatch {
-                    expected_typ: method.return_type.to_string(),
-                    expr_typ: meta.return_type().to_string(),
-                    expr_span: ret_type_span,
-                }
+                let expected_typ = trait_method.return_type.to_string();
+                let expr_typ = impl_method.return_type().to_string();
+                TypeCheckError::TypeMismatch { expr_typ, expected_typ, expr_span }
             });
 
             errors.extend(typecheck_errors.iter().cloned().map(|e| (e.into(), *file_id)));

compiler/noirc_frontend/src/hir/def_collector/errors.rs

@@ -41,14 +41,22 @@
     OverlappingImplNote { span: Span },
     #[error("Cannot `impl` a type defined outside the current crate")]
     ForeignImpl { span: Span, type_name: String },
-    #[error("Mismatch number of parameters in of trait implementation")]
+    #[error("Mismatched number of parameters in trait implementation")]
     MismatchTraitImplementationNumParameters {
         actual_num_parameters: usize,
         expected_num_parameters: usize,
         trait_name: String,
         method_name: String,
         span: Span,
     },
+    #[error("Mismatched number of generics in impl method")]
+    MismatchTraitImplementationNumGenerics {
+        impl_method_generic_count: usize,
+        trait_method_generic_count: usize,
+        trait_name: String,
+        method_name: String,
+        span: Span,
+    },
     #[error("Method is not defined in trait")]
     MethodNotInTrait { trait_name: Ident, impl_method: Ident },
     #[error("Only traits can be implemented")]
@@ -67,7 +75,7 @@
     TraitImplOrphaned { span: Span },
 
     // Aztec feature flag errors
     // TODO(benesjan): https://github.com/AztecProtocol/aztec-packages/issues/2905
     #[cfg(feature = "aztec")]
     #[error("Aztec dependency not found. Please add aztec as a dependency in your Cargo.toml")]
     AztecNotFound {},
@@ -174,8 +182,21 @@
                 method_name,
                 span,
             } => {
+                let plural = if expected_num_parameters == 1 { "" } else { "s" };
+                let primary_message = format!(
+                    "`{trait_name}::{method_name}` expects {expected_num_parameters} parameter{plural}, but this method has {actual_num_parameters}");
+                Diagnostic::simple_error(primary_message, "".to_string(), span)
+            }
+            DefCollectorErrorKind::MismatchTraitImplementationNumGenerics {
+                impl_method_generic_count,
+                trait_method_generic_count,
+                trait_name,
+                method_name,
+                span,
+            } => {
+                let plural = if trait_method_generic_count == 1 { "" } else { "s" };
                 let primary_message = format!(
-                    "Method `{method_name}` of trait `{trait_name}` needs {expected_num_parameters} parameters, but has {actual_num_parameters}");
+                    "`{trait_name}::{method_name}` expects {trait_method_generic_count} generic{plural}, but this method has {impl_method_generic_count}");
                 Diagnostic::simple_error(primary_message, "".to_string(), span)
             }
             DefCollectorErrorKind::MethodNotInTrait { trait_name, impl_method } => {

compiler/noirc_frontend/src/hir_def/types.rs

@@ -560,6 +560,21 @@ impl Type {
                 .all(|(_, field)| field.is_valid_for_program_input()),
         }
     }
+
+    /// Returns the number of `Forall`-quantified type variables on this type.
+    /// Returns 0 if this is not a Type::Forall
+    pub fn generic_count(&self) -> usize {
+        match self {
+            Type::Forall(generics, _) => generics.len(),
+            Type::TypeVariable(type_variable, _) | Type::NamedGeneric(type_variable, _) => {
+                match &*type_variable.borrow() {
+                    TypeBinding::Bound(binding) => binding.generic_count(),
+                    TypeBinding::Unbound(_) => 0,
+                }
+            }
+            _ => 0,
+        }
+    }
 }
 
 impl std::fmt::Display for Type {

tooling/nargo_cli/tests/compile_failure/trait_incorrect_generic_count/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "trait_incorrect_generic_count"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.18.0"
+
+[dependencies]

tooling/nargo_cli/tests/compile_failure/trait_incorrect_generic_count/src/main.nr

@@ -0,0 +1,13 @@
+
+fn main(){
+    let x: u32 = 0;
+    x.trait_fn();
+}
+
+trait Trait {
+    fn trait_fn<T>(x: T) -> T {}
+}
+
+impl Trait for u32 {
+    fn trait_fn<A, B>(x: A) -> A { x }
+}