From 35a20b4134d98e63e22a4879330c03f2f6577ece Mon Sep 17 00:00:00 2001
From: Andrew Morrow <acm@mongodb.com>
Date: Tue, 4 Jan 2022 18:08:01 -0500
Subject: SERVER-62324 Fix unique_function issues in C++20 mode with VS 2022

---
 src/mongo/stdx/type_traits.h | 33 ---------------------------------
 src/mongo/util/functional.h  |  2 +-
 2 files changed, 1 insertion(+), 34 deletions(-)

diff --git a/src/mongo/stdx/type_traits.h b/src/mongo/stdx/type_traits.h
index 62438228bba..f7187877b2a 100644
--- a/src/mongo/stdx/type_traits.h
+++ b/src/mongo/stdx/type_traits.h
@@ -92,39 +92,6 @@ struct conjunction<B> : B {};
 template <typename B1, typename... B>
 struct conjunction<B1, B...> : std::conditional_t<bool(B1::value), stdx::conjunction<B...>, B1> {};
 
-namespace detail {
-template <typename Func,
-          typename... Args,
-          typename = typename std::result_of<Func && (Args && ...)>::type>
-auto is_invocable_impl(Func&& func, Args&&... args) -> std::true_type;
-auto is_invocable_impl(...) -> std::false_type;
-}  // namespace detail
-
-template <typename Func, typename... Args>
-struct is_invocable
-    : decltype(detail::is_invocable_impl(std::declval<Func>(), std::declval<Args>()...)) {};
-
-namespace detail {
-
-// This helps solve the lack of regular void problem, when passing a 'conversion target' as a
-// parameter.
-
-template <typename R,
-          typename Func,
-          typename... Args,
-          typename ComputedResult = typename std::result_of<Func && (Args && ...)>::type>
-auto is_invocable_r_impl(stdx::type_identity<R>, Func&& func, Args&&... args) ->
-    typename stdx::disjunction<std::is_void<R>,
-                               std::is_same<ComputedResult, R>,
-                               std::is_convertible<ComputedResult, R>>::type;
-auto is_invocable_r_impl(...) -> std::false_type;
-}  // namespace detail
-
-template <typename R, typename Func, typename... Args>
-struct is_invocable_r
-    : decltype(detail::is_invocable_r_impl(
-          stdx::type_identity<R>(), std::declval<Func>(), std::declval<Args>()...)) {};
-
 }  // namespace stdx
 }  // namespace mongo
 
diff --git a/src/mongo/util/functional.h b/src/mongo/util/functional.h
index c30089a64e9..ca968ea9ca6 100644
--- a/src/mongo/util/functional.h
+++ b/src/mongo/util/functional.h
@@ -95,7 +95,7 @@ public:
         // requirements are met.  They must be concrete parameters not template parameters to work
         // around bugs in some compilers that we presently use.  We may be able to revisit this
         // design after toolchain upgrades for C++17.
-        std::enable_if_t<stdx::is_invocable_r<RetType, Functor, Args...>::value, TagType> =
+        std::enable_if_t<std::is_invocable_r<RetType, Functor, Args...>::value, TagType> =
             makeTag(),
         std::enable_if_t<std::is_move_constructible<Functor>::value, TagType> = makeTag(),
         std::enable_if_t<!std::is_same<std::decay_t<Functor>, unique_function>::value, TagType> =
-- 
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