field_to_json() in arrow_integration_test/ field.rs does not serialize fields metadata

[pshampanier]

Describe the bug
When calling arrow_integration_test::schema_to_json(schema) metadata at the field level are not serialized.

To Reproduce

#[cfg(test)]
mod tests {
    use arrow_integration_test::schema_to_json;
    use arrow_schema::{DataType, Field, Schema};
    use std::collections::HashMap;

    #[test]
    fn test_schema_to_json() {
        let metadata = [("key1".to_string(), "value1".to_string())].iter().cloned().collect::<HashMap<_, _>>();
        let fields = vec![Field::new("a", DataType::Int32, true).with_metadata(metadata.clone())];
        let schema = Schema::new(fields).with_metadata(metadata.clone());
        let json = schema_to_json(&schema);
        assert_eq!(
            serde_json::to_string_pretty(&json).unwrap(),
            serde_json::to_string_pretty(&serde_json::json!({
                "fields": [
                    {
                        "name": "a",
                        "nullable": true,
                        "type": {
                            "bitWidth": 32,
                            "isSigned": true,
                            "name": "int"
                        },
                        "children": [],
                        "metadata": {
                            "key1": "value1"
                        },
                    },
                ],
                "metadata": {
                    "key1": "value1"
                },
            }))
            .unwrap()
        );
    }
}

Expected behavior
Expected:

{
  "fields": [
    {
      "children": [],
      "metadata": {
        "key1": "value1"
      },
      "name": "a",
      "nullable": true,
      "type": {
        "bitWidth": 32,
        "isSigned": true,
        "name": "int"
      }
    }
  ],
  "metadata": {
    "key1": "value1"
  }
}

Found:

{
  "fields": [
    {
      "children": [],
      "name": "a",
      "nullable": true,
      "type": {
        "bitWidth": 32,
        "isSigned": true,
        "name": "int"
      }
    }
  ],
  "metadata": {
    "key1": "value1"
  }
}

The metadata key is available at the schema level but missing for fields.
Additional context
Tested with arrow version = "53.1.0"

[alamb]

Thanks for the report -- so that sounds like field metadata is being lost somewhere?

[pshampanier]

Not lost, just omitted at serialization:

arrow-rs/arrow-integration-test/src/field.rs

Lines 266 to 296 in 0e9abcd

	pub fn field_to_json(field: &Field) -> serde_json::Value {
	let children: Vec<serde_json::Value> = match field.data_type() {
	DataType::Struct(fields) => fields.iter().map(|x| field_to_json(x.as_ref())).collect(),
	DataType::List(field)
	| DataType::LargeList(field)
	| DataType::FixedSizeList(field, _)
	| DataType::Map(field, _) => vec![field_to_json(field)],
	_ => vec![],
	};
	match field.data_type() {
	DataType::Dictionary(ref index_type, ref value_type) => serde_json::json!({
	"name": field.name(),
	"nullable": field.is_nullable(),
	"type": data_type_to_json(value_type),
	"children": children,
	"dictionary": {
	"id": field.dict_id().unwrap(),
	"indexType": data_type_to_json(index_type),
	"isOrdered": field.dict_is_ordered().unwrap(),
	}
	}),
	_ => serde_json::json!({
	"name": field.name(),
	"nullable": field.is_nullable(),
	"type": data_type_to_json(field.data_type()),
	"children": children
	}),
	}
	}

Line 292 should be:

 "children": children,
 "metadata": serde_json::to_value(field.metadata()).unwrap()

Just like in:

arrow-rs/arrow-integration-test/src/schema.rs

Lines 24 to 29 in 0e9abcd

	pub fn schema_to_json(schema: &Schema) -> serde_json::Value {
	serde_json::json!({
	"fields": schema.fields().iter().map(|f| field_to_json(f.as_ref())).collect::<Vec<_>>(),
	"metadata": serde_json::to_value(schema.metadata()).unwrap()
	})
	}

I tested it, and it's working fine.

[alamb]

Would you be willing to create a PR to fix this issue @pshampanier ?

Thank you