Function validate_struct_compatibility

datafusion/common/src/nested_struct.rs:345–381

Validates compatibility between source and target struct fields for casting operations. This function implements comprehensive struct compatibility checking by examining: - Field name matching between source and target structs - Type castability for each matching field (including recursive struct validation) - Proper handling of missing fields (target fields not in source are allowed - filled wit

(
    source_fields: &[FieldRef],
    target_fields: &[FieldRef],
)

/// ```
///
pub fn validate_struct_compatibility(
    source_fields: &[FieldRef],
    target_fields: &[FieldRef],
) -> Result<()> {
    let has_overlap = has_one_of_more_common_fields(source_fields, target_fields);
    if !has_overlap {
        return _plan_err!(
            "Cannot cast struct with {} fields to {} fields because there is no field name overlap",
            source_fields.len(),
            target_fields.len()
        );
    }

    // Check compatibility for each target field
    for target_field in target_fields {
        // Look for matching field in source by name
        if let Some(source_field) = source_fields
            .iter()
            .find(|f| f.name() == target_field.name())
        {
            validate_field_compatibility(source_field, target_field)?;
        } else {
            // Target field is missing from source
            // If it's non-nullable, we cannot fill it with NULL
            if !target_field.is_nullable() {
                return _plan_err!(
                    "Cannot cast struct: target field '{}' is non-nullable but missing from source. \
                     Cannot fill with NULL.",
                    target_field.name()
                );
            }
        }
    }

    // Extra fields in source are OK - they'll be ignored
    Ok(())
}

fn validate_field_compatibility(
    source_field: &Field,