pub(crate) fn declared_expectation(ty: &Type) -> TokenStreamExpand description
The expression, on a conversion failure’s path, for what a parameter of
type ty declares when the macro has no wording for it: an
Option<String>, with the error bound as e. Only for a type the binding
converts with TryFromSexp, whose __MX_EXPECTATION it reads.
An Either (also under Missing) is worded side by side
(from_r::either_expectation, expected_arm), so one side the macro
does not know no longer leaves the whole parameter without an
expectation; any other type is asked for its __MX_EXPECTATION (a
#[derive(TryFromSexp)] newtype says what its inner type does). The
NULL or of an Option<_> parameter is the prefix’s (nullable).