Function variants_for_ty 

pub fn variants_for_ty(
    ty: TyId,
    tys: &Types,
    doc_text: &str,
    files: Option<&HashMap<PathBuf, String>>,
) -> Vec<Completion>

v0.145 (ADR 0169, base gap for #565): the variants offerable for a scrutinee Ty at a pattern position. A user-declared sum’s variants come from source (sum_type_variants); the built-in Result/Option variants do not (they are not declared types, so sum_type_variants can’t see them) and are intrinsic here. This is why match-arm / is completion now fires for a Result/Option scrutinee, not only a user sum.