fix: Variables from trait constraints being permanently bound over wh…

…en used within a trait impl (#4450)

# Description

## Problem\*

Resolves #4436 

## Summary\*

This issue stemmed from calling another trait method within an impl for
the trait. The trait method required a trait constraint of the same
trait to be valid and was using the trait with its original type
variables. These would later be bound over when an impl was searched for
for this trait.

I've added a somewhat hacky solution of avoiding inserting `t = t`
bindings from the trait constraint when checking identifiers. Avoiding
inserting this binding means `t` in this case will later be instantiated
to a fresh type variable later on in the `instantiate_with_bindings`
call.

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[Exceptional Case]** 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/hir/type_check/expr.rs

@@ -326,7 +326,10 @@ impl<'interner> TypeChecker<'interner> {
             assert_eq!(the_trait.generics.len(), constraint.trait_generics.len());
 
             for (param, arg) in the_trait.generics.iter().zip(&constraint.trait_generics) {
-                bindings.insert(param.id(), (param.clone(), arg.clone()));
+                // Avoid binding t = t
+                if !arg.occurs(param.id()) {
+                    bindings.insert(param.id(), (param.clone(), arg.clone()));
+                }
             }
         }
 

compiler/noirc_frontend/src/hir_def/types.rs

@@ -1558,7 +1558,7 @@ impl Type {
     }
 
     /// True if the given TypeVariableId is free anywhere within self
-    fn occurs(&self, target_id: TypeVariableId) -> bool {
+    pub fn occurs(&self, target_id: TypeVariableId) -> bool {
         match self {
             Type::Array(len, elem) => len.occurs(target_id) || elem.occurs(target_id),
             Type::String(len) => len.occurs(target_id),

test_programs/execution_success/regression_4436/Nargo.toml

@@ -0,0 +1,5 @@
+[package]
+name = "regression_4436"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.22.0"

test_programs/execution_success/regression_4436/src/main.nr

@@ -0,0 +1,31 @@
+trait LibTrait<N> {
+    fn broadcast();
+    fn get_constant() -> Field;
+}
+
+global STRUCT_A_LEN: Field = 3;
+global STRUCT_B_LEN: Field = 5;
+
+struct StructA;
+struct StructB;
+
+impl LibTrait<u32> for StructA {
+    fn broadcast() {
+        Self::get_constant();
+    }
+
+    fn get_constant() -> Field {
+        1
+    }
+}
+impl LibTrait<u64> for StructB {
+    fn broadcast() {
+        Self::get_constant();
+    }
+
+    fn get_constant() -> Field {
+        1
+    }
+}
+
+fn main() {}