fix: Fix scalar op lowering tree walk

bigframes/core/expression.py

@@ -253,6 +253,11 @@ def is_identity(self) -> bool:
     def transform_children(self, t: Callable[[Expression], Expression]) -> Expression:
         ...
 
+    def bottom_up(self, t: Callable[[Expression], Expression]) -> Expression:
+        expr = self.transform_children(lambda child: child.bottom_up(t))
+        expr = t(expr)
+        return expr
+
     def walk(self) -> Generator[Expression, None, None]:
         yield self
         for child in self.children:

bigframes/core/rewrite/op_lowering.py

@@ -44,7 +44,7 @@ def lower_expr_step(expr: expression.Expression) -> expression.Expression:
                     return maybe_rule.lower(expr)
             return expr
 
-        return lower_expr_step(expr.transform_children(lower_expr_step))
+        return expr.bottom_up(lower_expr_step)
 
     def lower_node(node: bigframe_node.BigFrameNode) -> bigframe_node.BigFrameNode:
         if isinstance(

tests/system/small/engines/test_generic_ops.py

@@ -423,3 +423,18 @@ def test_engines_isin_op(scalars_array_value: array_value.ArrayValue, engine):
     )
 
     assert_equivalence_execution(arr.node, REFERENCE_ENGINE, engine)
+
+
+@pytest.mark.parametrize("engine", ["polars", "bq"], indirect=True)
+def test_engines_isin_op_nested_filter(
+    scalars_array_value: array_value.ArrayValue, engine
+):
+    isin_clause = ops.IsInOp((1, 2, 3)).as_expr(expression.deref("int64_col"))
+    filter_clause = ops.invert_op.as_expr(
+        ops.or_op.as_expr(
+            expression.deref("bool_col"), ops.invert_op.as_expr(isin_clause)
+        )
+    )
+    arr = scalars_array_value.filter(filter_clause)
+
+    assert_equivalence_execution(arr.node, REFERENCE_ENGINE, engine)