Function native_borrow_checks 

pub(crate) fn native_borrow_checks<'a>(
    args: impl IntoIterator<Item = (usize, String, &'a Type)>,
    argv: &Ident,
    targets: Option<&[Ident]>,
) -> TokenStream

Check native arguments before conversion can create references. Arity must already be checked, and the caller must be inside the shim’s R unwind boundary. &Self uses ExternalPtr handles and its separate address check.