fix: Allow where clause on all functions and improve error message

compiler/noirc_frontend/src/hir/type_check/expr.rs

@@ -859,7 +859,7 @@ impl<'interner> TypeChecker<'interner> {
         method_name: &str,
         expr_id: &ExprId,
     ) -> Option<HirMethodReference> {
-        match object_type {
+        match object_type.follow_bindings() {
             Type::Struct(typ, _args) => {
                 let id = typ.borrow().id;
                 match self.interner.lookup_method(object_type, id, method_name, false) {
@@ -914,12 +914,20 @@ impl<'interner> TypeChecker<'interner> {
                 .interner
                 .lookup_primitive_trait_method_mut(element.as_ref(), method_name)
                 .map(HirMethodReference::FuncId)
-                .or_else(|| self.lookup_method(element, method_name, expr_id)),
+                .or_else(|| self.lookup_method(&element, method_name, expr_id)),
+
             // If we fail to resolve the object to a struct type, we have no way of type
             // checking its arguments as we can't even resolve the name of the function
             Type::Error => None,
 
-            other => match self.interner.lookup_primitive_method(other, method_name) {
+            // The type variable must be unbound at this point since follow_bindings was called
+            Type::TypeVariable(_, TypeVariableKind::Normal) => {
+                let span = self.interner.expr_span(expr_id);
+                self.errors.push(TypeCheckError::TypeAnnotationsNeeded { span });
+                None
+            }
+
+            other => match self.interner.lookup_primitive_method(&other, method_name) {
                 Some(method_id) => Some(HirMethodReference::FuncId(method_id)),
                 None => {
                     self.errors.push(TypeCheckError::UnresolvedMethodCall {

compiler/noirc_frontend/src/parser/errors.rs

@@ -30,8 +30,6 @@ pub enum ParserErrorReason {
     ComptimeDeprecated,
     #[error("{0} are experimental and aren't fully supported yet")]
     ExperimentalFeature(&'static str),
-    #[error("Where clauses are allowed only on functions with generic parameters")]
-    WhereClauseOnNonGenericFunction,
     #[error(
         "Multiple primary attributes found. Only one function attribute is allowed per function"
     )]

compiler/noirc_frontend/src/parser/parser.rs

@@ -177,12 +177,11 @@ fn function_definition(allow_self: bool) -> impl NoirParser<NoirFunction> {
             let ((((attributes, modifiers), name), generics), parameters) = args;
 
             // Validate collected attributes, filtering them into function and secondary variants
-            let attrs = validate_attributes(attributes, span, emit);
-            validate_where_clause(&generics, &where_clause, span, emit);
+            let attributes = validate_attributes(attributes, span, emit);
             FunctionDefinition {
                 span: body_span,
                 name,
-                attributes: attrs,
+                attributes,
                 is_unconstrained: modifiers.0,
                 is_open: modifiers.2,
                 is_internal: modifiers.3,
@@ -412,7 +411,6 @@ fn trait_definition() -> impl NoirParser<TopLevelStatement> {
         .then(trait_body())
         .then_ignore(just(Token::RightBrace))
         .validate(|(((name, generics), where_clause), items), span, emit| {
-            validate_where_clause(&generics, &where_clause, span, emit);
             emit(ParserError::with_reason(ParserErrorReason::ExperimentalFeature("Traits"), span));
             TopLevelStatement::Trait(NoirTrait { name, generics, where_clause, span, items })
         })
@@ -451,12 +449,9 @@ fn trait_function_declaration() -> impl NoirParser<TraitItem> {
         .then(function_return_type().map(|(_, typ)| typ))
         .then(where_clause())
         .then(trait_function_body_or_semicolon)
-        .validate(
-            |(((((name, generics), parameters), return_type), where_clause), body), span, emit| {
-                validate_where_clause(&generics, &where_clause, span, emit);
-                TraitItem::Function { name, generics, parameters, return_type, where_clause, body }
-            },
-        )
+        .map(|(((((name, generics), parameters), return_type), where_clause), body)| {
+            TraitItem::Function { name, generics, parameters, return_type, where_clause, body }
+        })
 }
 
 fn validate_attributes(
@@ -514,17 +509,6 @@ fn validate_struct_attributes(
     struct_attributes
 }
 
-fn validate_where_clause(
-    generics: &Vec<Ident>,
-    where_clause: &Vec<UnresolvedTraitConstraint>,
-    span: Span,
-    emit: &mut dyn FnMut(ParserError),
-) {
-    if !where_clause.is_empty() && generics.is_empty() {
-        emit(ParserError::with_reason(ParserErrorReason::WhereClauseOnNonGenericFunction, span));
-    }
-}
-
 /// Function declaration parameters differ from other parameters in that parameter
 /// patterns are not allowed in declarations. All parameters must be identifiers.
 fn function_declaration_parameters() -> impl NoirParser<Vec<(Ident, UnresolvedType)>> {
@@ -2133,7 +2117,6 @@ mod test {
                 "fn func_name<T>(f: Field, y : pub Field, z : pub [u8;5],) where T: {}",
                 "fn func_name<T>(f: Field, y : pub Field, z : pub [u8;5],) where SomeTrait {}",
                 "fn func_name<T>(f: Field, y : pub Field, z : pub [u8;5],) SomeTrait {}",
-                "fn func_name(f: Field, y : pub Field, z : pub [u8;5],) where T: SomeTrait {}",
                 // A leading plus is not allowed.
                 "fn func_name<T>(f: Field, y : T) where T: + SomeTrait {}",
                 "fn func_name<T>(f: Field, y : T) where T: TraitX + <Y> {}",
@@ -2164,11 +2147,7 @@ mod test {
 
         parse_all_failing(
             trait_definition(),
-            vec![
-                "trait MissingBody",
-                "trait WrongDelimiter { fn foo() -> u8, fn bar() -> u8 }",
-                "trait WhereClauseWithoutGenerics where A: SomeTrait { }",
-            ],
+            vec!["trait MissingBody", "trait WrongDelimiter { fn foo() -> u8, fn bar() -> u8 }"],
         );
     }