never is trivially const-drop, and add test

compiler/rustc_middle/src/ty/util.rs

@@ -1054,7 +1054,8 @@ pub fn trivial_const_drop<'tcx>(ty: Ty<'tcx>) -> bool {
         | ty::RawPtr(_)
         | ty::Ref(..)
         | ty::FnDef(..)
-        | ty::FnPtr(_) => true,
+        | ty::FnPtr(_)
+        | ty::Never => true,
 
         ty::Opaque(..)
         | ty::Dynamic(..)
@@ -1062,7 +1063,6 @@ pub fn trivial_const_drop<'tcx>(ty: Ty<'tcx>) -> bool {
         | ty::Bound(..)
         | ty::Param(_)
         | ty::Placeholder(_)
-        | ty::Never
         | ty::Foreign(_)
         | ty::Projection(_)
         | ty::Infer(_) => false,

src/test/ui/rfc-2632-const-trait-impl/const-drop.rs

@@ -3,6 +3,7 @@
 #![feature(const_trait_impl)]
 #![feature(const_fn_trait_bound)]
 #![feature(const_mut_refs)]
+#![feature(never_type)]
 #![cfg_attr(precise, feature(const_precise_live_drops))]
 
 struct S<'a>(&'a mut u8);
@@ -77,6 +78,7 @@ fn drop(&mut self) {
     &1,
     &1 as *const i32,
     ConstDropWithBound::<()>,
+    Result::<i32, !>::Ok(1),
 }
 
 fn main() {