ARROW-4589: [Rust] Projection push down query optimizer rule

rust/datafusion/src/lib.rs

@@ -27,4 +27,5 @@ extern crate sqlparser;
 pub mod dfparser;
 pub mod execution;
 pub mod logicalplan;
+pub mod optimizer;
 pub mod sqlplanner;

rust/datafusion/src/optimizer/mod.rs

@@ -0,0 +1,19 @@
+// 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.
+
+pub mod optimizer;
+pub mod projection_push_down;

rust/datafusion/src/optimizer/optimizer.rs

@@ -0,0 +1,27 @@
+// 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.
+
+//! Query optimizer traits
+
+use crate::logicalplan::LogicalPlan;
+use arrow::error::Result;
+use std::rc::Rc;
+
+/// An optimizer rules performs a transformation on a logical plan to produce an optimized logical plan.
+pub trait OptimizerRule {
+    fn optimize(&mut self, plan: &LogicalPlan) -> Result<Rc<LogicalPlan>>;
+}