Fix lint in a very hacky, fragile way.

Author: reitermarkus

compiler/rustc_lint/src/types.rs

@@ -1041,7 +1041,22 @@ fn get_nullable_type<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>>
             // must use an Option<fn(..) -> _> to represent it.
             ty
         }
+        ty::Alias(ty::Projection, alias_ty) => {
+            let ty::AliasTy { def_id, .. } = alias_ty;
+            debug!("get_nullable_type: alias def_id: {:?}", def_id);
 
+            let assoc_item = tcx.associated_item(def_id);
+            debug!("get_nullable_type: alias associated_item: {:?}", assoc_item);
+
+            // FIXME: Call `get_nullable_type` with the resolved `alias_ty`.
+            if assoc_item.name.as_str() == "NonZeroInner" {
+                // `<T as ZeroablePrimitive>::NonZeroInner`'s inner value is the same as `T`.
+                return Some(args.type_at(0));
+            }
+
+            debug!("get_nullable_type: unhandled alias: {:?} while checking {:?}", alias_ty, ty);
+            return None;
+        }
         // We should only ever reach this case if ty_is_known_nonnull is extended
         // to other types.
         ref unhandled => {