Macro rustc_middle::TrivialTypeFoldableImpls

macro_rules! TrivialTypeFoldableImpls {
    (for <$tcx:lifetime> { $($ty:ty,)+ }) => { ... };
    ($($ty:ty,)+) => { ... };
}

Used for types that are Copy and which do not care arena allocated data (i.e., don't need to be folded).