Function no_na_requirement 

pub(crate) fn no_na_requirement(ty: &Type) -> String

What a no_na parameter of Rust type ty must satisfy, without the parameter name: must not contain NA for a value holding several values (no_na_holds_several), else must not be NA.

Shared by the R guard and the Rust check that the C wrapper runs after the conversion (see no_na_message), so both word a failure alike.