add const_case_when_eval_rule & const_case_when_rewriter

src/frontend/src/binder/expr/mod.rs

@@ -504,7 +504,7 @@ impl Binder {
                 constant_lookup_inputs.push(input);
             } else {
                 // If at least one condition is not in the simple form / not constant,
-                // we can NOT do the subsequent optimization then
+                // we can NOT do the subsequent optimization pass
                 return false;
             }
 

src/frontend/src/optimizer/plan_expr_rewriter/const_case_when_rewriter.rs

@@ -0,0 +1,13 @@
+// Copyright 2024 RisingWave Labs
+//
+// 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.

src/frontend/src/optimizer/rule/const_case_when_eval_rule.rs

@@ -0,0 +1,29 @@
+// Copyright 2024 RisingWave Labs
+//
+// 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.
+
+use super::super::plan_node::*;
+use super::{BoxedRule, Rule};
+
+pub struct ConstCaseWhenEvalRule {}
+impl Rule for ConstCaseWhenEvalRule {
+    fn apply(&self, plan: PlanRef) -> Option<PlanRef> {
+        todo!()
+    }
+}
+
+impl ConstCaseWhenEvalRule {
+    pub fn create() -> BoxedRule {
+        Box::new(ConstCaseWhenEvalRule {})
+    }
+}