From aaac0f6bffbe11eb090145354f1b82919bb93cb7 Mon Sep 17 00:00:00 2001
From: Michael J Klein <michaeljklein@users.noreply.github.com>
Date: Mon, 29 Apr 2024 15:22:19 -0400
Subject: [PATCH] fix: ensure where clauses propagated to trait default
 definitions (#4894)

# Description

## Problem\*

Resolves https://github.com/noir-lang/noir/issues/4847

## Summary\*

Before this PR, we were simply copying the default definition as an
unresolved `impl` method, without adding in any `where` clauses from the
top level of the `impl`. This PR propagates the `where` clauses into
default definitions when they're used.

For example:

```rust
impl<T> Foo for Bar<T> where T: Foo {
    fn qux(self) -> bool {
                        ^ we want an implicit "where T: Foo" here
      ..
    }
}
```

## Additional Context



## 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.

---------

Co-authored-by: jfecher <jake@aztecprotocol.com>
---
 .../src/hir/resolution/traits.rs              | 11 +++++-----
 compiler/noirc_frontend/src/tests.rs          | 21 +++++++++++++++++++
 .../impl_from_where_impl/Nargo.toml           |  7 +++++++
 .../impl_from_where_impl/src/main.nr          | 15 +++++++++++++
 4 files changed, 49 insertions(+), 5 deletions(-)
 create mode 100644 test_programs/compile_success_empty/impl_from_where_impl/Nargo.toml
 create mode 100644 test_programs/compile_success_empty/impl_from_where_impl/src/main.nr

diff --git a/compiler/noirc_frontend/src/hir/resolution/traits.rs b/compiler/noirc_frontend/src/hir/resolution/traits.rs
index ccae8c6dd0..3d355fd444 100644
--- a/compiler/noirc_frontend/src/hir/resolution/traits.rs
+++ b/compiler/noirc_frontend/src/hir/resolution/traits.rs
@@ -124,6 +124,7 @@ fn resolve_trait_methods(
 
             let mut resolver = Resolver::new(interner, &path_resolver, def_maps, file);
             resolver.add_generics(generics);
+
             resolver.add_existing_generics(&unresolved_trait.trait_def.generics, trait_generics);
             resolver.add_existing_generic("Self", name_span, self_typevar);
             resolver.set_self_type(Some(self_type.clone()));
@@ -207,16 +208,16 @@ fn collect_trait_impl_methods(
 
         if overrides.is_empty() {
             if let Some(default_impl) = &method.default_impl {
+                // copy 'where' clause from unresolved trait impl
+                let mut default_impl_clone = default_impl.clone();
+                default_impl_clone.def.where_clause.extend(trait_impl.where_clause.clone());
+
                 let func_id = interner.push_empty_fn();
                 let module = ModuleId { local_id: trait_impl.module_id, krate: crate_id };
                 let location = Location::new(default_impl.def.span, trait_impl.file_id);
                 interner.push_function(func_id, &default_impl.def, module, location);
                 func_ids_in_trait.insert(func_id);
-                ordered_methods.push((
-                    method.default_impl_module_id,
-                    func_id,
-                    *default_impl.clone(),
-                ));
+                ordered_methods.push((method.default_impl_module_id, func_id, *default_impl_clone));
             } else {
                 let error = DefCollectorErrorKind::TraitMissingMethod {
                     trait_name: interner.get_trait(trait_id).name.clone(),
diff --git a/compiler/noirc_frontend/src/tests.rs b/compiler/noirc_frontend/src/tests.rs
index cf2d7dbe15..b2cc7eee9f 100644
--- a/compiler/noirc_frontend/src/tests.rs
+++ b/compiler/noirc_frontend/src/tests.rs
@@ -746,6 +746,27 @@ mod test {
         }
     }
 
+    #[test]
+    fn test_impl_self_within_default_def() {
+        let src = "
+        trait Bar {
+            fn ok(self) -> Self;
+
+            fn ref_ok(self) -> Self {
+                self.ok()
+            }
+        }
+
+        impl<T> Bar for (T, T) where T: Bar {
+            fn ok(self) -> Self {
+                self
+            }
+        }";
+        let errors = get_program_errors(src);
+        errors.iter().for_each(|err| println!("{:?}", err));
+        assert!(errors.is_empty());
+    }
+
     #[test]
     fn check_trait_as_type_as_fn_parameter() {
         let src = "
diff --git a/test_programs/compile_success_empty/impl_from_where_impl/Nargo.toml b/test_programs/compile_success_empty/impl_from_where_impl/Nargo.toml
new file mode 100644
index 0000000000..5894e457dd
--- /dev/null
+++ b/test_programs/compile_success_empty/impl_from_where_impl/Nargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "impl_from_where_impl"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.27.0"
+
+[dependencies]
diff --git a/test_programs/compile_success_empty/impl_from_where_impl/src/main.nr b/test_programs/compile_success_empty/impl_from_where_impl/src/main.nr
new file mode 100644
index 0000000000..3cec46bdfc
--- /dev/null
+++ b/test_programs/compile_success_empty/impl_from_where_impl/src/main.nr
@@ -0,0 +1,15 @@
+trait Bar {
+    fn ok(self) -> Self;
+
+    fn ref_ok(self) -> Self {
+        self.ok()
+    }
+}
+
+impl<T> Bar for (T, T) where T: Bar {
+    fn ok(self) -> Self {
+        self
+    }
+}
+
+fn main() {}