[GitHub] [arrow-datafusion] avantgardnerio commented on a diff in pull request #2892: Adds optional serde support to datafusion-proto

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

avantgardnerio commented on code in PR #2892:
URL: https://github.com/apache/arrow-datafusion/pull/2892#discussion_r920312561


##########
datafusion/proto/src/lib.rs:
##########
@@ -75,19 +78,32 @@ mod roundtrip_tests {
     use std::fmt::Formatter;
     use std::sync::Arc;
 
+    #[cfg(feature = "serde")]
+    fn roundtrip_serde_test(proto: &protobuf::LogicalExprNode) {
+        let string = serde_json::to_string(proto).unwrap();
+        let back: protobuf::LogicalExprNode = serde_json::from_str(&string).unwrap();
+        assert_eq!(proto, &back);
+    }
+
+    #[cfg(not(feature = "serde"))]
+    fn roundtrip_serde_test(_proto: &protobuf::LogicalExprNode) {}
+
     // Given a DataFusion logical Expr, convert it to protobuf and back, using debug formatting to test
     // equality.
-    macro_rules! roundtrip_expr_test {
-        ($initial_struct:ident, $ctx:ident) => {
-            let proto: protobuf::LogicalExprNode = (&$initial_struct).try_into().unwrap();
+    fn roundtrip_expr_test<T, E>(initial_struct: T, ctx: SessionContext)
+    where
+        for<'a> &'a T: TryInto<protobuf::LogicalExprNode, Error = E> + Debug,
+        E: Debug,
+    {
+        let proto: protobuf::LogicalExprNode = (&initial_struct).try_into().unwrap();
+        let round_trip: Expr = parse_expr(&proto, &ctx).unwrap();

Review Comment:
   Thanks for making this PR! I'm sure it's a step in the correct direction, but after cloning it, I'm having trouble figuring out how to extend it to include `LogicalPlan`s as well. There appears to be no equivalent `parse_plan()`?
   
   If I'm reading this correctly, it looks like the protobuf generator generated an entirely separate copy of all the Expr & LogicalPlan enums, and we created some fairly large functions to convert back and forth between them like `parse_expr`? If so the next step would be to write `parse_plan`?
   
   It does look from other tests like we are able to roundtrip plans to protobuf, so maybe I am missing something. When I tried: 
   
   ```
           let protobuf =
               protobuf::LogicalPlanNode::try_from_logical_plan(&topk_plan, &extension_codec)?;
           let string = serde_json::to_string(&protobuf).unwrap();
           ```
           
           I get 
           
           ```
           139  |         let string = serde_json::to_string(&protobuf).unwrap();
        |                      --------------------- ^^^^^^^^^ the trait `serde::ser::Serialize` is not implemented for `LogicalPlanNode`
        |                      |
        |                      required by a bound introduced by this call
        ```
        Sorry, I'm a bit lost. Any help is appreciated :)



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