Function parse_composite_unique_attribute 

pub fn parse_composite_unique_attribute(
    raw: &str,
) -> Result<ParsedCompositeUnique, String>

Parses @@unique([field1, field2, ...], where: "...") into its ordered list of local field names plus an optional partial-index predicate. Callers are responsible for checking that each name resolves to a real scalar field on the model.