[ty] Add cycle handling to lazy_default (#20967)

crates/ty_python_semantic/src/types.rs

@@ -8344,7 +8344,7 @@ impl<'db> TypeVarInstance<'db> {
         Some(TypeVarBoundOrConstraints::Constraints(ty))
     }
 
-    #[salsa::tracked(heap_size=ruff_memory_usage::heap_size)]
+    #[salsa::tracked(cycle_initial=lazy_default_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
     fn lazy_default(self, db: &'db dyn Db) -> Option<Type<'db>> {
         let definition = self.definition(db)?;
         let module = parsed_module(db, definition.file(db)).load(db);
@@ -8391,6 +8391,13 @@ fn lazy_bound_or_constraints_cycle_initial<'db>(
     None
 }
 
+fn lazy_default_cycle_initial<'db>(
+    _db: &'db dyn Db,
+    _self: TypeVarInstance<'db>,
+) -> Option<Type<'db>> {
+    None
+}
+
 /// Where a type variable is bound and usable.
 #[derive(
     Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd, salsa::Update, get_size2::GetSize,