Function external_member_signatures 

fn external_member_signatures<'gcx>(
    gcx: Gcx<'gcx>,
    hir: &Hir<'gcx>,
    base: &Expr<'gcx>,
    member_name: Symbol,
    explicit_arg_count: usize,
) -> Vec<(Visibility, StateMutability)>

(visibility, state_mutability) for every callable member named member_name. When explicit_arg_count matches one or more overloads, narrows to those; otherwise returns the full set. Preserves overloads (no unique collapse).