fix: Variables from trait constraints being permanently bound over when used within a trait impl

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

@@ -1526,7 +1526,7 @@
                 Type::Tuple(fields)
             }
             Type::Forall(typevars, typ) => {
                 // Trying to substitute_helper a variable de, substitute_bound_typevarsfined within a nested Forall
                 // is usually impossible and indicative of an error in the type checker somewhere.
                 for var in typevars {
                     assert!(!type_bindings.contains_key(&var.id()));
@@ -1558,7 +1558,7 @@
     }
 
     /// 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() {}