From 5b1280600d2129bf9b2ce8b73343878533b82056 Mon Sep 17 00:00:00 2001
From: Allison Vacanti <allison.vacanti@kitware.com>
Date: Fri, 20 Dec 2019 16:17:30 -0500
Subject: [PATCH] Cleanup reference types when using declval.

When expanding variadic parameter packs in ArrayHandleDecorator
implementations, make sure that the types used are appropriate.
Since std::declval is used to test whether or not a method with
specific arguments exists, it is important that the reference types
are correct to ensure that the detection works as expected.

Portals are always passed to implementation functions as rvalue
references, and array handles are always passed as lvalue refs.
---
 vtkm/cont/ArrayHandleDecorator.h | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/vtkm/cont/ArrayHandleDecorator.h b/vtkm/cont/ArrayHandleDecorator.h
index 95af9e594..2ef8d9419 100644
--- a/vtkm/cont/ArrayHandleDecorator.h
+++ b/vtkm/cont/ArrayHandleDecorator.h
@@ -125,11 +125,9 @@ template <typename DecoratorImplT, template <typename...> class List, typename..
 struct IsFunctorInvertibleImpl<DecoratorImplT, List<PortalTs...>>
 {
 private:
-  using PortalList = brigand::list<typename std::decay<PortalTs>::type...>;
-
   template <
     typename T,
-    typename U = decltype(std::declval<T>().CreateInverseFunctor(std::declval<PortalTs>()...))>
+    typename U = decltype(std::declval<T>().CreateInverseFunctor(std::declval<PortalTs&&>()...))>
   static std::true_type InverseExistsTest(int);
 
   template <typename T>
@@ -147,7 +145,8 @@ struct GetFunctorTypeImpl;
 template <typename DecoratorImplT, template <typename...> class List, typename... PortalTs>
 struct GetFunctorTypeImpl<DecoratorImplT, List<PortalTs...>>
 {
-  using type = decltype(std::declval<DecoratorImplT>().CreateFunctor(std::declval<PortalTs>()...));
+  using type =
+    decltype(std::declval<DecoratorImplT>().CreateFunctor(std::declval<PortalTs&&>()...));
 };
 
 // Deduces the type returned by DecoratorImplT::CreateInverseFunctor when given
@@ -160,7 +159,7 @@ template <typename DecoratorImplT, template <typename...> class List, typename..
 struct GetInverseFunctorTypeImpl<std::true_type, DecoratorImplT, List<PortalTs...>>
 {
   using type =
-    decltype(std::declval<DecoratorImplT>().CreateInverseFunctor(std::declval<PortalTs>()...));
+    decltype(std::declval<DecoratorImplT>().CreateInverseFunctor(std::declval<PortalTs&&>()...));
 };
 
 template <typename DecoratorImplT, typename PortalList>
@@ -328,19 +327,19 @@ using GetInverseFunctorType =
 // - So we jump through some decltype/declval hoops here to get this to work:
 template <typename... ArrayTs>
 using GetPortalConstControlList =
-  brigand::list<decltype((GetPortalConstControl(std::declval<ArrayTs>())))...>;
+  brigand::list<decltype((GetPortalConstControl(std::declval<ArrayTs&>())))...>;
 
 template <typename Device, typename... ArrayTs>
 using GetPortalConstExecutionList =
-  brigand::list<decltype((GetPortalInput(std::declval<ArrayTs>(), Device{})))...>;
+  brigand::list<decltype((GetPortalInput(std::declval<ArrayTs&>(), Device{})))...>;
 
 template <typename... ArrayTs>
 using GetPortalControlList =
-  brigand::list<decltype((GetPortalControl(std::declval<ArrayTs>())))...>;
+  brigand::list<decltype((GetPortalControl(std::declval<ArrayTs&>())))...>;
 
 template <typename Device, typename... ArrayTs>
 using GetPortalExecutionList =
-  brigand::list<decltype((GetPortalInPlace(std::declval<ArrayTs>(), Device{})))...>;
+  brigand::list<decltype((GetPortalInPlace(std::declval<ArrayTs&>(), Device{})))...>;
 
 template <typename DecoratorImplT, typename... ArrayTs>
 struct DecoratorStorageTraits