Function validate_field_compatibility

datafusion/common/src/nested_struct.rs:383–415

(
    source_field: &Field,
    target_field: &Field,
)

}

fn validate_field_compatibility(
    source_field: &Field,
    target_field: &Field,
) -> Result<()> {
    if source_field.data_type() == &DataType::Null {
        // Validate that target allows nulls before returning early.
        // It is invalid to cast a NULL source field to a non-nullable target field.
        if !target_field.is_nullable() {
            return _plan_err!(
                "Cannot cast NULL struct field '{}' to non-nullable field '{}'",
                source_field.name(),
                target_field.name()
            );
        }
        return Ok(());
    }

    // Ensure nullability is compatible. It is invalid to cast a nullable
    // source field to a non-nullable target field as this may discard
    // null values.
    if source_field.is_nullable() && !target_field.is_nullable() {
        return _plan_err!(
            "Cannot cast nullable struct field '{}' to non-nullable field",
            target_field.name()
        );
    }

    validate_data_type_compatibility(
        target_field.name(),
        source_field.data_type(),
        target_field.data_type(),
    )
}

/// Validates that `source_type` can be cast to `target_type`, recursively
/// handling container types that wrap structs.