From cec63902c52710ba7df433eda310296f7b7652d2 Mon Sep 17 00:00:00 2001
From: Ary Borenszweig <asterite@gmail.com>
Date: Tue, 23 Jul 2024 17:18:16 -0300
Subject: [PATCH] fix: lookup trait constraints methods in composite types
 (#5595)

# Description

## Problem

Resolves #5186

## Summary

Looking for methods that are bound to trait constraints was already
working for `NamedGeneric`, but when the trait is on a composite type,
like `(T, U)` or even `(T, i32)` methods weren't lookup up in
constraints bound to those types.

We only lookup this in case the regular (`lookup_primitive_method`)
lookup fails to find something.

## Additional Context

None.

## Documentation

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.
---
 .../noirc_frontend/src/elaborator/types.rs    | 80 ++++++++++---------
 compiler/noirc_frontend/src/tests.rs          | 15 ++++
 2 files changed, 58 insertions(+), 37 deletions(-)

diff --git a/compiler/noirc_frontend/src/elaborator/types.rs b/compiler/noirc_frontend/src/elaborator/types.rs
index d5dbb170843..f884d76dbf7 100644
--- a/compiler/noirc_frontend/src/elaborator/types.rs
+++ b/compiler/noirc_frontend/src/elaborator/types.rs
@@ -1211,37 +1211,7 @@ impl<'context> Elaborator<'context> {
                 None
             }
             Type::NamedGeneric(_, _, _) => {
-                let func_id = match self.current_item {
-                    Some(DependencyId::Function(id)) => id,
-                    _ => panic!("unexpected method outside a function"),
-                };
-                let func_meta = self.interner.function_meta(&func_id);
-
-                for constraint in &func_meta.trait_constraints {
-                    if *object_type == constraint.typ {
-                        if let Some(the_trait) = self.interner.try_get_trait(constraint.trait_id) {
-                            for (method_index, method) in the_trait.methods.iter().enumerate() {
-                                if method.name.0.contents == method_name {
-                                    let trait_method = TraitMethodId {
-                                        trait_id: constraint.trait_id,
-                                        method_index,
-                                    };
-                                    return Some(HirMethodReference::TraitMethodId(
-                                        trait_method,
-                                        constraint.trait_generics.clone(),
-                                    ));
-                                }
-                            }
-                        }
-                    }
-                }
-
-                self.push_err(TypeCheckError::UnresolvedMethodCall {
-                    method_name: method_name.to_string(),
-                    object_type: object_type.clone(),
-                    span,
-                });
-                None
+                self.lookup_method_in_trait_constraints(object_type, method_name, span)
             }
             // Mutable references to another type should resolve to methods of their element type.
             // This may be a struct or a primitive type.
@@ -1264,17 +1234,53 @@ impl<'context> Elaborator<'context> {
             other => match self.interner.lookup_primitive_method(&other, method_name) {
                 Some(method_id) => Some(HirMethodReference::FuncId(method_id)),
                 None => {
-                    self.push_err(TypeCheckError::UnresolvedMethodCall {
-                        method_name: method_name.to_string(),
-                        object_type: object_type.clone(),
-                        span,
-                    });
-                    None
+                    // It could be that this type is a composite type that is bound to a trait,
+                    // for example `x: (T, U) ... where (T, U): SomeTrait`
+                    // (so this case is a generalization of the NamedGeneric case)
+                    self.lookup_method_in_trait_constraints(object_type, method_name, span)
                 }
             },
         }
     }
 
+    fn lookup_method_in_trait_constraints(
+        &mut self,
+        object_type: &Type,
+        method_name: &str,
+        span: Span,
+    ) -> Option<HirMethodReference> {
+        let func_id = match self.current_item {
+            Some(DependencyId::Function(id)) => id,
+            _ => panic!("unexpected method outside a function"),
+        };
+        let func_meta = self.interner.function_meta(&func_id);
+
+        for constraint in &func_meta.trait_constraints {
+            if *object_type == constraint.typ {
+                if let Some(the_trait) = self.interner.try_get_trait(constraint.trait_id) {
+                    for (method_index, method) in the_trait.methods.iter().enumerate() {
+                        if method.name.0.contents == method_name {
+                            let trait_method =
+                                TraitMethodId { trait_id: constraint.trait_id, method_index };
+                            return Some(HirMethodReference::TraitMethodId(
+                                trait_method,
+                                constraint.trait_generics.clone(),
+                            ));
+                        }
+                    }
+                }
+            }
+        }
+
+        self.push_err(TypeCheckError::UnresolvedMethodCall {
+            method_name: method_name.to_string(),
+            object_type: object_type.clone(),
+            span,
+        });
+
+        None
+    }
+
     pub(super) fn type_check_call(
         &mut self,
         call: &HirCallExpression,
diff --git a/compiler/noirc_frontend/src/tests.rs b/compiler/noirc_frontend/src/tests.rs
index c29d9b03c7a..80ec22139dd 100644
--- a/compiler/noirc_frontend/src/tests.rs
+++ b/compiler/noirc_frontend/src/tests.rs
@@ -2522,3 +2522,18 @@ fn duplicate_struct_field() {
     assert_eq!(first_def.span().start(), 26);
     assert_eq!(second_def.span().start(), 42);
 }
+
+#[test]
+fn trait_constraint_on_tuple_type() {
+    let src = r#"
+        trait Foo<A> {
+            fn foo(self, x: A) -> bool;
+        }
+
+        fn bar<T, U, V>(x: (T, U), y: V) -> bool where (T, U): Foo<V> {
+            x.foo(y)
+        }
+
+        fn main() {}"#;
+    assert_no_errors(src);
+}