fix(experimental elaborator): Fix frontend tests when `--use-elaborat…

…or` flag is specified (noir-lang#5145)

# Description

## Problem\*

Resolves noir-lang#5146

Fixes all failing frontend tests with the elaborator

## Summary\*

This PR includes a few fixes:
- Use `check_trait_impl_method_matches_declaration` to issue errors when
a trait impl method is declared with an incorrect signature.
- `define_function_meta` for default trait functions on impls when
they're copied over. Also make sure to set `self.current_trait_impl` and
`self.self_type` for them as well.
- Use `try_get_trait_implementation` when getting a trait impl may fail
(which may happen if there was a previous error resolving the trait for
that impl). This was triggering on the test where we tried to declare a
trait impl implementing a struct rather than a trait.
- `check_trait_wrong_parameter_type` has a duplicate error on master but
not in the elaborator so I changed the expected error count there.

## Additional Context

After this PR all existing code _should_ work with the elaborator and we
can get the word out to get others testing the `--use-elaborator` flag
for any errors/panics.

## 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.

compiler/noirc_frontend/src/elaborator/mod.rs

@@ -15,7 +15,7 @@ use crate::{
         },
         resolution::{errors::ResolverError, path_resolver::PathResolver, resolver::LambdaContext},
         scope::ScopeForest as GenericScopeForest,
-        type_check::TypeCheckError,
+        type_check::{check_trait_impl_method_matches_declaration, TypeCheckError},
     },
     hir_def::{expr::HirIdent, function::Parameters, traits::TraitConstraint},
     macros_api::{
@@ -851,6 +851,12 @@ impl<'context> Elaborator<'context> {
         self.generics = trait_impl.resolved_generics;
         self.current_trait_impl = trait_impl.impl_id;
 
+        for (module, function, _) in &trait_impl.methods.functions {
+            self.local_module = *module;
+            let errors = check_trait_impl_method_matches_declaration(self.interner, *function);
+            self.errors.extend(errors.into_iter().map(|error| (error.into(), self.file)));
+        }
+
         self.elaborate_functions(trait_impl.methods);
 
         self.self_type = None;
@@ -877,25 +883,26 @@ impl<'context> Elaborator<'context> {
     fn collect_trait_impl(&mut self, trait_impl: &mut UnresolvedTraitImpl) {
         self.local_module = trait_impl.module_id;
         self.file = trait_impl.file_id;
+        self.current_trait_impl = trait_impl.impl_id;
         trait_impl.trait_id = self.resolve_trait_by_path(trait_impl.trait_path.clone());
 
         let self_type = trait_impl.methods.self_type.clone();
         let self_type =
             self_type.expect("Expected struct type to be set before collect_trait_impl");
 
+        self.self_type = Some(self_type.clone());
         let self_type_span = trait_impl.object_type.span;
 
         if matches!(self_type, Type::MutableReference(_)) {
             let span = self_type_span.unwrap_or_else(|| trait_impl.trait_path.span());
             self.push_err(DefCollectorErrorKind::MutableReferenceInTraitImpl { span });
         }
 
-        assert!(trait_impl.trait_id.is_some());
         if let Some(trait_id) = trait_impl.trait_id {
+            self.generics = trait_impl.resolved_generics.clone();
             self.collect_trait_impl_methods(trait_id, trait_impl);
 
             let span = trait_impl.object_type.span.expect("All trait self types should have spans");
-            self.generics = trait_impl.resolved_generics.clone();
             self.declare_methods_on_struct(true, &mut trait_impl.methods, span);
 
             let methods = trait_impl.methods.function_ids();
@@ -945,6 +952,8 @@ impl<'context> Elaborator<'context> {
         }
 
         self.generics.clear();
+        self.current_trait_impl = None;
+        self.self_type = None;
     }
 
     fn get_module_mut(&mut self, module: ModuleId) -> &mut ModuleData {
@@ -1059,6 +1068,7 @@ impl<'context> Elaborator<'context> {
                     let module = self.module_id();
                     let location = Location::new(default_impl.def.span, trait_impl.file_id);
                     self.interner.push_function(func_id, &default_impl.def, module, location);
+                    self.define_function_meta(&mut default_impl_clone, func_id, false);
                     func_ids_in_trait.insert(func_id);
                     ordered_methods.push((
                         method.default_impl_module_id,

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

@@ -237,7 +237,13 @@ pub(crate) fn check_trait_impl_method_matches_declaration(
 
     let impl_ =
         meta.trait_impl.expect("Trait impl function should have a corresponding trait impl");
-    let impl_ = interner.get_trait_implementation(impl_);
+
+    // If the trait implementation is not defined in the interner then there was a previous
+    // error in resolving the trait path and there is likely no trait for this impl.
+    let Some(impl_) = interner.try_get_trait_implementation(impl_) else {
+        return errors;
+    };
+
     let impl_ = impl_.borrow();
     let trait_info = interner.get_trait(impl_.trait_id);
 

compiler/noirc_frontend/src/node_interner.rs

@@ -1145,6 +1145,10 @@ impl NodeInterner {
         }
     }
 
+    pub fn try_get_trait_implementation(&self, id: TraitImplId) -> Option<Shared<TraitImpl>> {
+        self.trait_implementations.get(&id).cloned()
+    }
+
     pub fn get_trait_implementation(&self, id: TraitImplId) -> Shared<TraitImpl> {
         self.trait_implementations[&id].clone()
     }

compiler/noirc_frontend/src/tests.rs

@@ -494,7 +494,10 @@ fn check_trait_wrong_parameter_type() {
     }";
     let errors = get_program_errors(src);
     assert!(!has_parser_error(&errors));
-    assert!(errors.len() == 2, "Expected 2 errors, got: {:?}", errors);
+
+    // This is a duplicate error in the name resolver & type checker.
+    // In the elaborator there is no duplicate and only 1 error is issued
+    assert!(errors.len() <= 2, "Expected 1 or 2 errors, got: {:?}", errors);
 
     for (err, _file_id) in errors {
         match &err {
@@ -593,22 +596,20 @@ fn check_impl_struct_not_trait() {
         bar: Field,
         array: [Field; 2],
     }
-    
+
     struct Default {
         x: Field,
         z: Field, 
     }
     
-    // Default is struct not a trait
+    // Default is a struct not a trait
     impl Default for Foo {
         fn default(x: Field, y: Field) -> Self {
             Self { bar: x, array: [x,y] }
         }
     }
     
-    fn main() {
-    }
-    
+    fn main() {}
     ";
     let errors = get_program_errors(src);
     assert!(!has_parser_error(&errors));