Added check before adding constants to constant folding map.

Closes #5967.

crates/cairo-lang-lowering/src/optimizations/const_folding.rs

@@ -95,7 +95,17 @@ pub fn const_folding(db: &dyn LoweringGroup, lowered: &mut FlatLowered) {
             maybe_replace_inputs(&var_info, stmt.inputs_mut());
             match stmt {
                 Statement::Const(StatementConst { value, output }) => {
-                    var_info.insert(*output, VarInfo::Const(value.clone()));
+                    // Preventing the insertion of non-member consts values (such as a `Box` of a
+                    // const).
+                    if matches!(
+                        value,
+                        ConstValue::Int(..)
+                            | ConstValue::Struct(..)
+                            | ConstValue::Enum(..)
+                            | ConstValue::NonZero(..)
+                    ) {
+                        var_info.insert(*output, VarInfo::Const(value.clone()));
+                    }
                 }
                 Statement::Snapshot(stmt) => {
                     if let Some(VarInfo::Const(val)) = var_info.get(&stmt.input.var_id) {

tests/bug_samples/issue5967.cairo

@@ -0,0 +1,23 @@
+#[derive(Drop)]
+pub enum Pattern {
+    Leaf,
+    Boxed: Box<Pattern>
+}
+
+pub fn boxed(pat: Pattern) -> Pattern {
+    return Pattern::Boxed(BoxTrait::new(pat));
+}
+
+pub fn boxed_leaf() -> Pattern {
+    boxed(Pattern::Leaf)
+}
+
+#[inline(never)]
+pub fn boxed_boxed_leaf() -> Pattern {
+    boxed(boxed_leaf())
+}
+
+#[test]
+fn test() {
+    let _ = boxed_boxed_leaf();
+}

tests/bug_samples/lib.cairo

@@ -46,6 +46,7 @@ mod issue5438;
 mod issue5629;
 mod issue5680;
 mod issue5764;
+mod issue5967;
 mod loop_break_in_match;
 mod loop_only_change;
 mod partial_param_local;