[GitHub] [arrow] westonpace commented on a diff in pull request #13537: ARROW-16988: [C++] Introduce Substrait ToProto/FromProto conversion options

[GitBox <gi...@apache.org>]

westonpace commented on code in PR #13537:
URL: https://github.com/apache/arrow/pull/13537#discussion_r920302519


##########
cpp/src/arrow/engine/substrait/options.h:
##########
@@ -0,0 +1,55 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you 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.
+
+// This API is EXPERIMENTAL.
+
+#pragma once
+
+namespace arrow {
+namespace engine {
+
+/// How strictly to adhere to the input structure when converting between Substrait and
+/// Acero representations of a plan. This allows the user to trade conversion accuracy
+/// for performance and lenience.
+enum class ConversionStrictness {
+  /// Prevent information loss by rejecting incoming plans that use features or contain
+  /// metadata that cannot be exactly represented in the output format in a way that
+  /// will round-trip. Relations/nodes must map one-to-one.

Review Comment:
   ```suggestion
     /// will round-trip. Relations/nodes must map one-to-one.
     ///
     /// For example, any "hint" that Acero does not recognize will cause
     /// conversion to fail.
   ```



##########
cpp/src/arrow/engine/substrait/options.h:
##########
@@ -0,0 +1,55 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you 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.
+
+// This API is EXPERIMENTAL.
+
+#pragma once
+
+namespace arrow {
+namespace engine {
+
+/// How strictly to adhere to the input structure when converting between Substrait and
+/// Acero representations of a plan. This allows the user to trade conversion accuracy
+/// for performance and lenience.
+enum class ConversionStrictness {
+  /// Prevent information loss by rejecting incoming plans that use features or contain
+  /// metadata that cannot be exactly represented in the output format in a way that
+  /// will round-trip. Relations/nodes must map one-to-one.
+  PEDANTIC,
+
+  /// When an incoming plan uses a feature that cannot be exactly represented in the
+  /// output format, attempt to emulate that feature as opposed to immediately
+  /// rejecting the plan. For example, a Substrait SortRel with a complex sort key
+  /// expression may be emulated using a project-order-project triple. Relations/nodes
+  /// will thus map one-to-many.

Review Comment:
   ```suggestion
     /// expression may be emulated using a project-order-project triple.
   ```
   
   I'm not sure this last sentence is needed.  I could imagine a scenario might exist where this would result in a many-to-one as well (or one to zero) if a node is deemed supplementary.



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