Add check for empty schema in parquet::schema::types::from_thrift_helper

parquet/src/arrow/arrow_writer/mod.rs

@@ -3409,4 +3409,34 @@ mod tests {
             "Arrow: Incompatible type. Field 'temperature' has type Float64, array has type Int32"
         );
     }
+
+    #[test]
+    // https://github.com/apache/arrow-rs/issues/6988
+    fn test_roundtrip_empty_schema() {
+        // create empty record batch with empty schema
+        let empty_batch = RecordBatch::try_new_with_options(
+            Arc::new(Schema::empty()),
+            vec![],
+            &RecordBatchOptions::default().with_row_count(Some(0)),
+        )
+        .unwrap();
+
+        // write to parquet
+        let mut parquet_bytes: Vec<u8> = Vec::new();
+        let mut writer =
+            ArrowWriter::try_new(&mut parquet_bytes, empty_batch.schema(), None).unwrap();
+        writer.write(&empty_batch).unwrap();
+        writer.close().unwrap();
+
+        // read from parquet
+        let bytes = Bytes::from(parquet_bytes);
+        let reader = ParquetRecordBatchReaderBuilder::try_new(bytes).unwrap();
+        assert_eq!(reader.schema(), &empty_batch.schema());
+        let batches: Vec<_> = reader
+            .build()
+            .unwrap()
+            .collect::<ArrowResult<Vec<_>>>()
+            .unwrap();
+        assert_eq!(batches.len(), 0);
+    }
 }

parquet/src/schema/types.rs

@@ -1211,6 +1211,13 @@ fn from_thrift_helper(elements: &[SchemaElement], index: usize) -> Result<(usize
         ));
     }
     let element = &elements[index];
+
+    // Check for empty schema
+    if let (true, None | Some(0)) = (is_root_node, element.num_children) {
+        let builder = Type::group_type_builder(&element.name);
+        return Ok((index + 1, Arc::new(builder.build().unwrap())));
+    }
+
     let converted_type = ConvertedType::try_from(element.converted_type)?;
     // LogicalType is only present in v2 Parquet files. ConvertedType is always
     // populated, regardless of the version of the file (v1 or v2).