[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #2357: WIP: simplify_expressions no longer panics on unsupported evaluations

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

alamb commented on code in PR #2357:
URL: https://github.com/apache/arrow-datafusion/pull/2357#discussion_r860189248


##########
datafusion/core/src/optimizer/simplify_expressions.rs:
##########
@@ -400,9 +402,9 @@ impl<'a> ConstEvaluator<'a> {
     }
 
     /// Internal helper to evaluates an Expr
-    pub(crate) fn evaluate_to_scalar(&self, expr: Expr) -> Result<ScalarValue> {
+    pub(crate) fn evaluate_to_scalar(&self, expr: &Expr) -> Result<ScalarValue> {
         if let Expr::Literal(s) = expr {
-            return Ok(s);
+            return Ok(s.clone());

Review Comment:
   The `clone` is unfortunate -- I wonder if there is some way to pass it back. Like for example a signature such as  he following (aka return the `Expr` as the error if the evaluation doesn't work)?
   
   Maybe with some debugging messages on error (via `debug!`) would be sufficent?
   
   ```rust
       pub(crate) fn evaluate_to_scalar(&self, expr: Expr) -> std::result::Result<ScalarValue, Expr> {
   ```



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