[I] Align the logic for variant_get with arrow-cast when Variant::Object value inside a list [arrow-rs]

["klion26 (via GitHub)" <gi...@apache.org>]

klion26 opened a new issue, #10982:
URL: https://github.com/apache/arrow-rs/issues/10982

   By calling `variant_to_string` recursively we drop the `Variant::Object` values inside a list.
   
   arrow-cast doesn't support Objects -> String, but supports them inside a List [via `ArrayFormatter`](https://github.com/apache/arrow-rs/blob/70219af2ffa16615e2fcde5760b0218f5c986ac6/arrow-cast/src/display.rs#L1244-L1261) 🤷 (separate issue maybe?)
   
   regardless of correctness of the Object support above, variant-cast to String shouldn't lose data.
   
   ```rust
     #[test]
     fn reproduce_list_of_objects_utf8_difference() {
         // Build the Variant value: [{"x": 1}]
         let mut variant_builder = VariantBuilder::new();
         let mut variant_list = variant_builder.new_list();
   
         variant_list
             .new_object()
             .with_field("x", 1_i32)
             .finish();
   
         variant_list.finish();
   
         let (metadata, value) = variant_builder.finish();
         let variant = Variant::new(&metadata, &value);
   
         // Current #10114 result
         let variant_output = variant_to_string(&variant).unwrap();
   
         // Build the equivalent Arrow List<Struct<x: Int32>>
         let fields = vec![Field::new("x", DataType::Int32, true)];
         let struct_builder = StructBuilder::from_fields(fields, 1);
         let mut arrow_list = ListBuilder::new(struct_builder);
   
         let struct_builder = arrow_list.values();
         struct_builder
             .field_builder::<Int32Builder>(0)
             .unwrap()
             .append_value(1);
         struct_builder.append(true);
         arrow_list.append(true);
   
         let arrow_list = arrow_list.finish();
   
         // Arrow List<Struct> → Utf8 result
         let casted = cast(&arrow_list, &DataType::Utf8).unwrap();
         let arrow_output = casted.as_string::<i32>().value(0);
   
         assert_eq!(variant_output, "[]");
         assert_eq!(arrow_output, "[{x: 1}]");
   
         // Fails
         assert_eq!(variant_output, arrow_output);
     }
   ```
   
   _Originally posted by @sdf-jkl in https://github.com/apache/arrow-rs/pull/10114#discussion_r3908535499_
               


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Re: [I] Align the logic for variant_get with arrow-cast when Variant::Object value inside a list [arrow-rs]

["sdf-jkl (via GitHub)" <gi...@apache.org>]

sdf-jkl closed issue #10982: Align the logic for variant_get with arrow-cast when Variant::Object value inside a list
URL: https://github.com/apache/arrow-rs/issues/10982


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