Fix rolling window result types for empty inputs.

cpp/include/cudf/detail/aggregation/aggregation.hpp

@@ -784,9 +784,10 @@ struct target_type_impl<Source, aggregation::ALL> {
 // Except for chrono types where result is chrono. (Use FloorDiv)
 // TODO: MEAN should be only be enabled for duration types - not for timestamps
 template <typename Source, aggregation::Kind k>
-struct target_type_impl<Source,
-                        k,
-                        std::enable_if_t<!is_chrono<Source>() && (k == aggregation::MEAN)>> {
+struct target_type_impl<
+  Source,
+  k,
+  std::enable_if_t<is_fixed_width<Source>() && !is_chrono<Source>() && (k == aggregation::MEAN)>> {
   using type = double;
 };
 
@@ -1032,7 +1033,7 @@ template <typename Element>
 struct dispatch_aggregation {
 #pragma nv_exec_check_disable
   template <aggregation::Kind k, typename F, typename... Ts>
-  CUDA_HOST_DEVICE_CALLABLE decltype(auto) operator()(F&& f, Ts&&... args) const noexcept
+  CUDA_HOST_DEVICE_CALLABLE decltype(auto) operator()(F&& f, Ts&&... args) const
   {
     return f.template operator()<Element, k>(std::forward<Ts>(args)...);
   }
@@ -1043,7 +1044,7 @@ struct dispatch_source {
   template <typename Element, typename F, typename... Ts>
   CUDA_HOST_DEVICE_CALLABLE decltype(auto) operator()(aggregation::Kind k,
                                                       F&& f,
-                                                      Ts&&... args) const noexcept
+                                                      Ts&&... args) const
   {
     return aggregation_dispatcher(
       k, dispatch_aggregation<Element>{}, std::forward<F>(f), std::forward<Ts>(args)...);

cpp/src/rolling/grouped_rolling.cu

@@ -94,7 +94,7 @@ std::unique_ptr<column> grouped_rolling_window(table_view const& group_keys,
 {
   CUDF_FUNC_RANGE();
 
-  if (input.is_empty()) return empty_like(input);
+  if (input.is_empty()) { return cudf::detail::empty_output(input, aggr); }
 
   CUDF_EXPECTS((group_keys.num_columns() == 0 || group_keys.num_rows() == input.size()),
                "Size mismatch between group_keys and input vector.");
@@ -949,7 +949,7 @@ std::unique_ptr<column> grouped_range_rolling_window(table_view const& group_key
 {
   CUDF_FUNC_RANGE();
 
-  if (input.is_empty()) return empty_like(input);
+  if (input.is_empty()) { return cudf::detail::empty_output(input, aggr); }
 
   CUDF_EXPECTS((group_keys.num_columns() == 0 || group_keys.num_rows() == input.size()),
                "Size mismatch between group_keys and input vector.");

cpp/src/rolling/rolling.cu

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <cudf/detail/aggregation/aggregation.hpp>
 #include "rolling_detail.cuh"
 
 namespace cudf {
@@ -46,7 +47,8 @@ std::unique_ptr<column> rolling_window(column_view const& input,
 {
   CUDF_FUNC_RANGE();
 
-  if (input.is_empty()) return empty_like(input);
+  if (input.is_empty()) { return cudf::detail::empty_output(input, agg); }
+
   CUDF_EXPECTS((min_periods >= 0), "min_periods must be non-negative");
 
   CUDF_EXPECTS((default_outputs.is_empty() || default_outputs.size() == input.size()),
@@ -88,8 +90,9 @@ std::unique_ptr<column> rolling_window(column_view const& input,
 {
   CUDF_FUNC_RANGE();
 
-  if (preceding_window.is_empty() || following_window.is_empty() || input.is_empty())
-    return empty_like(input);
+  if (preceding_window.is_empty() || following_window.is_empty() || input.is_empty()) {
+    return cudf::detail::empty_output(input, agg);
+  }
 
   CUDF_EXPECTS(preceding_window.type().id() == type_id::INT32 &&
                  following_window.type().id() == type_id::INT32,

cpp/src/rolling/rolling_detail.cuh

@@ -309,6 +309,35 @@ struct DeviceRollingRowNumber {
   }
 };
 
+struct agg_specific_empty_output {
+  template <typename InputType, aggregation::Kind op>
+  std::unique_ptr<column> operator()(column_view const& input, rolling_aggregation const& agg) const
+  {
+    using target_type = cudf::detail::target_type_t<InputType, op>;
+
+    if constexpr (std::is_same_v<cudf::detail::target_type_t<InputType, op>, void>) {
+      CUDF_FAIL("Unsupported combination of column-type and aggregation.");
+    }
+
+    if constexpr (cudf::is_fixed_width<target_type>()) {
+      return cudf::make_empty_column(data_type{type_to_id<target_type>()});
+    }
+
+    if constexpr (op == aggregation::COLLECT_LIST) {
+      return cudf::make_lists_column(
+        0, make_empty_column(data_type{type_to_id<offset_type>()}), empty_like(input), 0, {});
+    }
+
+    return empty_like(input);
+  }
+};
+
+std::unique_ptr<column> empty_output(column_view const& input, rolling_aggregation const& agg)
+{
+  return cudf::detail::dispatch_type_and_aggregation(
+    input.type(), agg.kind, agg_specific_empty_output{}, input, agg);
+}
+
 /**
  * @brief Operator for applying a LEAD rolling aggregation on a single window.
  */
@@ -1061,7 +1090,7 @@ std::unique_ptr<column> rolling_window(column_view const& input,
   static_assert(warp_size == cudf::detail::size_in_bits<cudf::bitmask_type>(),
                 "bitmask_type size does not match CUDA warp size");
 
-  if (input.is_empty()) { return empty_like(input); }
+  if (input.is_empty()) { return cudf::detail::empty_output(input, agg); }
 
   if (cudf::is_dictionary(input.type())) {
     CUDF_EXPECTS(agg.kind == aggregation::COUNT_ALL || agg.kind == aggregation::COUNT_VALID ||

cpp/tests/CMakeLists.txt

@@ -280,12 +280,13 @@ ConfigureTest(STREAM_COMPACTION_TEST
 ###################################################################################################
 # - rolling tests ---------------------------------------------------------------------------------
 ConfigureTest(ROLLING_TEST
-    rolling/rolling_test.cpp
-    rolling/grouped_rolling_test.cpp
+    rolling/collect_list_test.cpp
+    rolling/empty_input_test.cpp
     rolling/lead_lag_test.cpp
-    rolling/range_window_bounds_test.cpp
+    rolling/grouped_rolling_test.cpp
     rolling/range_rolling_window_test.cpp
-    rolling/collect_list_test.cpp)
+    rolling/range_window_bounds_test.cpp
+    rolling/rolling_test.cpp)
 
 ###################################################################################################
 # - filling test ----------------------------------------------------------------------------------