Explicitly disable groupby on unsupported key types.

cpp/src/groupby/groupby.cu

@@ -55,6 +55,9 @@ groupby::groupby(table_view const& keys,
     _column_order{column_order},
     _null_precedence{null_precedence}
 {
+  auto is_list  = [](auto const& col) { return col.type().id() == cudf::type_id::LIST; };
+  auto has_list = std::any_of(keys.begin(), keys.end(), is_list);
+  CUDF_EXPECTS(not has_list, "Groupby does not support LIST columns as keys.");
 }
 
 // Select hash vs. sort groupby implementation

cpp/tests/CMakeLists.txt

@@ -62,6 +62,7 @@ ConfigureTest(GROUPBY_TEST
     groupby/count_tests.cpp
     groupby/groups_tests.cpp
     groupby/keys_tests.cpp
+    groupby/lists_tests.cpp
     groupby/m2_tests.cpp
     groupby/min_tests.cpp
     groupby/max_scan_tests.cpp

cpp/tests/groupby/lists_tests.cpp

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2021, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <tests/groupby/groupby_test_util.hpp>
+
+#include <cudf_test/base_fixture.hpp>
+#include <cudf_test/column_wrapper.hpp>
+#include <cudf_test/iterator_utilities.hpp>
+#include <cudf_test/type_lists.hpp>
+
+#include <cudf/detail/aggregation/aggregation.hpp>
+
+namespace cudf {
+namespace test {
+
+template <typename V>
+struct groupby_lists_test : public cudf::test::BaseFixture {
+};
+
+TYPED_TEST_SUITE(groupby_lists_test, cudf::test::FixedWidthTypes);
+
+namespace {
+// Checking with a single aggregation, and aggregation column.
+// This test is orthogonal to the aggregation type; it focuses on testing the grouping
+// with LISTS keys.
+auto sum_agg() { return cudf::make_sum_aggregation<groupby_aggregation>(); }
+
+void test_sort_based_sum_agg(column_view const& keys, column_view const& values)
+{
+  test_single_agg(
+    keys, values, keys, values, sum_agg(), force_use_sort_impl::YES, null_policy::INCLUDE);
+}
+
+void test_hash_based_sum_agg(column_view const& keys, column_view const& values)
+{
+  test_single_agg(
+    keys, values, keys, values, sum_agg(), force_use_sort_impl::NO, null_policy::INCLUDE);
+}
+
+}  // namespace
+
+TYPED_TEST(groupby_lists_test, top_level_lists_are_unsupported)
+{
+  // Test that grouping on LISTS columns fails visibly.
+
+  // clang-format off
+  auto keys   = lists_column_wrapper<TypeParam, int32_t> { {1,1},  {2,2},  {3,3},   {1,1},   {2,2} };
+  auto values = fixed_width_column_wrapper<int32_t>      {     0,      1,      2,      3,       4  };
+  // clang-format on
+
+  EXPECT_THROW(test_sort_based_sum_agg(keys, values), cudf::logic_error);
+  EXPECT_THROW(test_hash_based_sum_agg(keys, values), cudf::logic_error);
+}
+
+}  // namespace test
+}  // namespace cudf

cpp/tests/groupby/structs_tests.cpp

@@ -22,8 +22,6 @@
 #include <cudf_test/type_lists.hpp>
 
 #include <cudf/detail/aggregation/aggregation.hpp>
-#include "cudf/aggregation.hpp"
-#include "cudf/types.hpp"
 
 using namespace cudf::test::iterators;
 
@@ -34,7 +32,7 @@ template <typename V>
 struct groupby_structs_test : public cudf::test::BaseFixture {
 };
 
-TYPED_TEST_CASE(groupby_structs_test, cudf::test::FixedWidthTypes);
+TYPED_TEST_SUITE(groupby_structs_test, cudf::test::FixedWidthTypes);
 
 using V       = int32_t;  // Type of Aggregation Column.
 using M0      = int32_t;  // Type of STRUCT's first (i.e. 0th) member.
@@ -79,27 +77,43 @@ void print_agg_results(column_view const& keys, column_view const& vals)
   }
 }
 
-void test_sum_agg(column_view const& keys,
-                  column_view const& values,
-                  column_view const& expected_keys,
-                  column_view const& expected_values)
+void test_sort_based_sum_agg(column_view const& keys,
+                             column_view const& values,
+                             column_view const& expected_keys,
+                             column_view const& expected_values)
 {
   test_single_agg(keys,
                   values,
                   expected_keys,
                   expected_values,
                   sum_agg(),
-                  force_use_sort_impl::NO,
+                  force_use_sort_impl::YES,
                   null_policy::INCLUDE);
+}
+
+void test_hash_based_sum_agg(column_view const& keys,
+                             column_view const& values,
+                             column_view const& expected_keys,
+                             column_view const& expected_values)
+{
   test_single_agg(keys,
                   values,
                   expected_keys,
                   expected_values,
                   sum_agg(),
-                  force_use_sort_impl::YES,
+                  force_use_sort_impl::NO,
                   null_policy::INCLUDE);
 }
 
+void test_sum_agg(column_view const& keys,
+                  column_view const& values,
+                  column_view const& expected_keys,
+                  column_view const& expected_values)
+{
+  test_sort_based_sum_agg(keys, values, expected_keys, expected_values);
+  test_hash_based_sum_agg(keys, values, expected_keys, expected_values);
+}
+
 }  // namespace
 
 TYPED_TEST(groupby_structs_test, basic)
@@ -312,7 +326,8 @@ TYPED_TEST(groupby_structs_test, lists_are_unsupported)
   // clang-format on
   auto keys = structs{{member_0, member_1}};
 
-  EXPECT_THROW(test_sum_agg(keys, values, keys, values), cudf::logic_error);
+  EXPECT_THROW(test_sort_based_sum_agg(keys, values, keys, values), cudf::logic_error);
+  EXPECT_THROW(test_hash_based_sum_agg(keys, values, keys, values), cudf::logic_error);
 }
 
 }  // namespace test