Function variants_of 

pub fn variants_of(
    ty: TyId,
    types: &HashMap<String, Arc<TypeDecl>>,
    tys: &Types,
) -> Option<Vec<VariantInfo>>

pub since P6.4 (#1157, Decision A) — see VariantInfo’s own doc comment for why bynk-emit needs this exact function rather than a re-derived copy (R5.11, for the IR side).