[GitHub] [arrow-datafusion] jackwener commented on a diff in pull request #3810: Make expression manipulation consistent and easier to use: `combine/split filter` `conjunction`, etc

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

jackwener commented on code in PR #3810:
URL: https://github.com/apache/arrow-datafusion/pull/3810#discussion_r994609709


##########
datafusion/optimizer/src/utils.rs:
##########
@@ -424,31 +468,74 @@ mod tests {
     use super::*;
     use arrow::datatypes::DataType;
     use datafusion_common::Column;
-    use datafusion_expr::{binary_expr, col, lit, utils::expr_to_columns};
+    use datafusion_expr::{col, lit, utils::expr_to_columns};
     use std::collections::HashSet;
     use std::ops::Add;
 
     #[test]
-    fn combine_zero_filters() {
-        let result = combine_filters(&[]);
-        assert_eq!(result, None);
+    fn test_split_conjunction() {

Review Comment:
   IMO, I think we can add test for `conjunction()`. At the same time, we can check the tree structure of this expression by using `match`.
   
   ```rs
   expr is (A B) C;
   
   /// using `match` to check.
   match expr {
      And(
         And(
            B,
            C
         ),
         C
      )
   }
   ```
   
   [A, B, C ,D , E] -> (((A B) C) (D E)) is different from ((((A B) C) D) E).
   
   we can see the result of `conjunction()` in the UT
   
   



##########
datafusion/optimizer/src/utils.rs:
##########
@@ -51,62 +51,106 @@ pub fn optimize_children(
     from_plan(plan, &new_exprs, &new_inputs)
 }
 
-/// converts "A AND B AND C" => [A, B, C]
-pub fn split_conjunction<'a>(predicate: &'a Expr, predicates: &mut Vec<&'a Expr>) {
-    match predicate {
+/// Splits a conjunctive [`Expr`] such as `A AND B AND C` => `[A, B, C]`
+///
+/// See [`split_conjunction_owned`] for more details and an example.
+pub fn split_conjunction(expr: &Expr) -> Vec<&Expr> {
+    split_conjunction_impl(expr, vec![])
+}
+
+fn split_conjunction_impl<'a>(expr: &'a Expr, mut exprs: Vec<&'a Expr>) -> Vec<&'a Expr> {
+    match expr {
         Expr::BinaryExpr {
             right,
             op: Operator::And,
             left,
         } => {
-            split_conjunction(left, predicates);
-            split_conjunction(right, predicates);
+            let exprs = split_conjunction_impl(left, exprs);
+            split_conjunction_impl(right, exprs)
         }
-        Expr::Alias(expr, _) => {
-            split_conjunction(expr, predicates);
+        Expr::Alias(expr, _) => split_conjunction_impl(expr, exprs),

Review Comment:
   👍



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