fix: Nested arrays should not get a field in lookup (#18745)

## Which issue does this PR close?

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- Closes #18744 .

## Rationale for this change

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in the issue then this section is not needed.
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your changes and offer better suggestions for fixes.
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Fixes a critical bug, as well as behaves more like avro expects in
regards to arrays.

## What changes are included in this PR?

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is sometimes worth providing a summary of the individual changes in this
PR.
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Removed the sub label from arrays in general

## Are these changes tested?

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Yes

## Are there any user-facing changes?

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Not really

Author: EmilyMatt

datafusion/datasource-avro/src/avro_to_arrow/arrow_array_reader.rs

@@ -132,9 +132,8 @@ impl<R: Read> AvroArrowArrayReader<'_, R> {
                 }
             }
             AvroSchema::Array(schema) => {
-                let sub_parent_field_name = format!("{parent_field_name}.element");
                 Self::child_schema_lookup(
-                    &sub_parent_field_name,
+                    parent_field_name,
                     &schema.items,
                     schema_lookup,
                 )?;
@@ -596,10 +595,7 @@ impl<R: Read> AvroArrowArrayReader<'_, R> {
                     })
                     .collect();
 
-                let sub_parent_field_name =
-                    format!("{}.{}", parent_field_name, list_field.name());
-                let arrays =
-                    self.build_struct_array(&rows, &sub_parent_field_name, fields)?;
+                let arrays = self.build_struct_array(&rows, parent_field_name, fields)?;
                 let data_type = DataType::Struct(fields.clone());
                 ArrayDataBuilder::new(data_type)
                     .len(rows.len())
@@ -1038,7 +1034,7 @@ where
 mod test {
     use crate::avro_to_arrow::{Reader, ReaderBuilder};
     use arrow::array::Array;
-    use arrow::datatypes::DataType;
+    use arrow::datatypes::{DataType, Fields};
     use arrow::datatypes::{Field, TimeUnit};
     use datafusion_common::assert_batches_eq;
     use datafusion_common::cast::{
@@ -1720,4 +1716,92 @@ mod test {
         assert_eq!(2, num_batches);
         assert_eq!(28, sum_id);
     }
+
+    #[test]
+    fn test_list_of_structs_with_custom_field_name() {
+        let schema = apache_avro::Schema::parse_str(
+            r#"
+        {
+          "type": "record",
+          "name": "root",
+          "fields": [
+            {
+              "name": "items",
+              "type": {
+                "type": "array",
+                "items": {
+                  "type": "record",
+                  "name": "item_record",
+                  "fields": [
+                    {
+                      "name": "id",
+                      "type": "long"
+                    },
+                    {
+                      "name": "name",
+                      "type": "string"
+                    }
+                  ]
+                }
+              }
+            }
+          ]
+        }"#,
+        )
+        .unwrap();
+
+        let r1 = apache_avro::to_value(serde_json::json!({
+            "items": [
+                {
+                    "id": 1,
+                    "name": "first"
+                },
+                {
+                    "id": 2,
+                    "name": "second"
+                }
+            ]
+        }))
+        .unwrap()
+        .resolve(&schema)
+        .unwrap();
+
+        let mut w = apache_avro::Writer::new(&schema, vec![]);
+        w.append(r1).unwrap();
+        let bytes = w.into_inner().unwrap();
+
+        // Create an Arrow schema where the list field is NOT named "element"
+        let arrow_schema = Arc::new(arrow::datatypes::Schema::new(vec![Field::new(
+            "items",
+            DataType::List(Arc::new(Field::new(
+                "item", // This is NOT "element"
+                DataType::Struct(Fields::from(vec![
+                    Field::new("id", DataType::Int64, false),
+                    Field::new("name", DataType::Utf8, false),
+                ])),
+                false,
+            ))),
+            false,
+        )]));
+
+        let mut reader = ReaderBuilder::new()
+            .with_schema(arrow_schema)
+            .with_batch_size(10)
+            .build(std::io::Cursor::new(bytes))
+            .unwrap();
+
+        // This used to fail because schema_lookup would have "items.element.id" and "items.element.name"
+        // but build_struct_array will try to look up "items.item.id" and "items.item.name",
+        // Now it it is simply "items.id" and "items.name"
+        let batch = reader.next().unwrap().unwrap();
+
+        let expected = [
+            "+-----------------------------------------------+",
+            "| items                                         |",
+            "+-----------------------------------------------+",
+            "| [{id: 1, name: first}, {id: 2, name: second}] |",
+            "+-----------------------------------------------+",
+        ];
+        assert_batches_eq!(expected, &[batch]);
+    }
 }