Account for C++17 deferred temporary materialization in invocable_r (#1282)

Co-authored-by: Stephan T. Lavavej <[email protected]>

Author: CaseyCarter

stl/inc/type_traits

@@ -1657,6 +1657,32 @@ template <class _From, class _To>
 using is_nothrow_convertible = _Is_nothrow_convertible<_From, _To>;
 #endif // _HAS_CXX20
 
+template <class _Ty>
+_Ty _Returns_exactly() noexcept; // not defined
+
+template <class _From, class _To, class = void>
+struct _Invoke_convertible : false_type {};
+
+template <class _From, class _To>
+struct _Invoke_convertible<_From, _To, void_t<decltype(_Implicitly_convert_to<_To>(_Returns_exactly<_From>()))>>
+    : true_type {};
+
+template <class _From, class _To>
+struct _Invoke_nothrow_convertible : bool_constant<noexcept(_Implicitly_convert_to<_To>(_Returns_exactly<_From>()))> {};
+
+template <class _Result, bool _Nothrow>
+struct _Invoke_traits_common {
+    using type                  = _Result;
+    using _Is_invocable         = true_type;
+    using _Is_nothrow_invocable = bool_constant<_Nothrow>;
+    template <class _Rx>
+    using _Is_invocable_r = bool_constant<disjunction_v<is_void<_Rx>, _Invoke_convertible<type, _Rx>>>;
+    template <class _Rx>
+    using _Is_nothrow_invocable_r = bool_constant<conjunction_v<_Is_nothrow_invocable,
+        disjunction<is_void<_Rx>,
+            conjunction<_Invoke_convertible<type, _Rx>, _Invoke_nothrow_convertible<type, _Rx>>>>>;
+};
+
 template <class _Void, class _Callable>
 struct _Invoke_traits_zero {
     // selected when _Callable isn't callable with zero _Args
@@ -1672,17 +1698,8 @@ template <class _Callable>
 using _Decltype_invoke_zero = decltype(_STD declval<_Callable>()());
 
 template <class _Callable>
-struct _Invoke_traits_zero<void_t<_Decltype_invoke_zero<_Callable>>, _Callable> {
-    // selected when _Callable is callable with zero _Args
-    using type                  = _Decltype_invoke_zero<_Callable>;
-    using _Is_invocable         = true_type;
-    using _Is_nothrow_invocable = bool_constant<noexcept(_STD declval<_Callable>()())>;
-    template <class _Rx>
-    using _Is_invocable_r = bool_constant<disjunction_v<is_void<_Rx>, is_convertible<type, _Rx>>>;
-    template <class _Rx>
-    using _Is_nothrow_invocable_r = bool_constant<
-        conjunction_v<_Is_nothrow_invocable, disjunction<is_void<_Rx>, _Is_nothrow_convertible<type, _Rx>>>>;
-};
+struct _Invoke_traits_zero<void_t<_Decltype_invoke_zero<_Callable>>, _Callable>
+    : _Invoke_traits_common<_Decltype_invoke_zero<_Callable>, noexcept(_STD declval<_Callable>()())> {};
 
 template <class _Void, class... _Types>
 struct _Invoke_traits_nonzero {
@@ -1701,18 +1718,9 @@ using _Decltype_invoke_nonzero = decltype(
 
 template <class _Callable, class _Ty1, class... _Types2>
 struct _Invoke_traits_nonzero<void_t<_Decltype_invoke_nonzero<_Callable, _Ty1, _Types2...>>, _Callable, _Ty1,
-    _Types2...> {
-    // selected when _Callable is callable with nonzero _Args
-    using type                  = _Decltype_invoke_nonzero<_Callable, _Ty1, _Types2...>;
-    using _Is_invocable         = true_type;
-    using _Is_nothrow_invocable = bool_constant<noexcept(_Invoker1<_Callable, _Ty1>::_Call(
-        _STD declval<_Callable>(), _STD declval<_Ty1>(), _STD declval<_Types2>()...))>;
-    template <class _Rx>
-    using _Is_invocable_r = bool_constant<disjunction_v<is_void<_Rx>, is_convertible<type, _Rx>>>;
-    template <class _Rx>
-    using _Is_nothrow_invocable_r = bool_constant<
-        conjunction_v<_Is_nothrow_invocable, disjunction<is_void<_Rx>, _Is_nothrow_convertible<type, _Rx>>>>;
-};
+    _Types2...> : _Invoke_traits_common<_Decltype_invoke_nonzero<_Callable, _Ty1, _Types2...>,
+                      noexcept(_Invoker1<_Callable, _Ty1>::_Call(
+                          _STD declval<_Callable>(), _STD declval<_Ty1>(), _STD declval<_Types2>()...))> {};
 
 template <class _Callable, class... _Args>
 using _Select_invoke_traits = conditional_t<sizeof...(_Args) == 0, _Invoke_traits_zero<void, _Callable>,

tests/std/tests/VSO_0105317_expression_sfinae/test.cpp

@@ -19,14 +19,16 @@ using namespace std;
 #if _HAS_CXX17
 template <typename Void, typename Callable, typename... Args>
 struct HasInvokeResultT : false_type {
-
     STATIC_ASSERT(!is_invocable_v<Callable, Args...>);
+    STATIC_ASSERT(!is_nothrow_invocable_v<Callable, Args...>);
+    STATIC_ASSERT(!is_invocable_r_v<void, Callable, Args...>);
+    STATIC_ASSERT(!is_nothrow_invocable_r_v<void, Callable, Args...>);
 };
 
 template <typename Callable, typename... Args>
 struct HasInvokeResultT<void_t<invoke_result_t<Callable, Args...>>, Callable, Args...> : true_type {
-
     STATIC_ASSERT(is_invocable_v<Callable, Args...>);
+    STATIC_ASSERT(is_invocable_r_v<void, Callable, Args...>);
 };
 
 template <typename A>
@@ -584,6 +586,12 @@ STATIC_ASSERT(is_nothrow_invocable_r_v<long, Kitty, int>);
 STATIC_ASSERT(is_invocable_r_v<long, Kitty, int, int>);
 STATIC_ASSERT(!is_nothrow_invocable_r_v<long, Kitty, int, int>);
 
+// When the return type is void, does the invocation throw?
+STATIC_ASSERT(is_invocable_r_v<void, Kitty, int>);
+STATIC_ASSERT(is_nothrow_invocable_r_v<void, Kitty, int>);
+STATIC_ASSERT(is_invocable_r_v<void, Kitty, int, int>);
+STATIC_ASSERT(!is_nothrow_invocable_r_v<void, Kitty, int, int>);
+
 struct Puppy {
     explicit Puppy(int);
     Puppy(long) noexcept;
@@ -605,6 +613,38 @@ STATIC_ASSERT(is_nothrow_invocable_r_v<Puppy, Kitty, int>);
 STATIC_ASSERT(is_invocable_r_v<Zebra, Kitty, int>);
 STATIC_ASSERT(!is_nothrow_invocable_r_v<Zebra, Kitty, int>);
 
+#if defined(__clang__) || defined(__EDG__) // TRANSITION, VSO-1026729
+// Defend against regression of VSO-963790, in which is_invocable_r mishandles non-movable return types
+struct NonMovable {
+    NonMovable(NonMovable&&)      = delete;
+    NonMovable(const NonMovable&) = delete;
+};
+
+template <bool Nothrow>
+NonMovable getNonMovable() noexcept(Nothrow);
+
+STATIC_ASSERT(is_invocable_r_v<NonMovable, decltype(&getNonMovable<false>)>);
+STATIC_ASSERT(is_invocable_r_v<NonMovable, decltype(&getNonMovable<true>)>);
+STATIC_ASSERT(!is_nothrow_invocable_r_v<NonMovable, decltype(&getNonMovable<false>)>);
+STATIC_ASSERT(is_nothrow_invocable_r_v<NonMovable, decltype(&getNonMovable<true>)>);
+
+template <bool Nothrow>
+struct ConvertsToNonMovable {
+    operator NonMovable() const noexcept(Nothrow);
+};
+
+template <bool Nothrow, bool NothrowReturn>
+ConvertsToNonMovable<NothrowReturn> getConvertsToNonMovable() noexcept(Nothrow);
+
+STATIC_ASSERT(is_invocable_r_v<NonMovable, decltype(&getConvertsToNonMovable<false, false>)>);
+STATIC_ASSERT(is_invocable_r_v<NonMovable, decltype(&getConvertsToNonMovable<false, true>)>);
+STATIC_ASSERT(is_invocable_r_v<NonMovable, decltype(&getConvertsToNonMovable<true, false>)>);
+STATIC_ASSERT(is_invocable_r_v<NonMovable, decltype(&getConvertsToNonMovable<true, true>)>);
+STATIC_ASSERT(!is_nothrow_invocable_r_v<NonMovable, decltype(&getConvertsToNonMovable<false, false>)>);
+STATIC_ASSERT(!is_nothrow_invocable_r_v<NonMovable, decltype(&getConvertsToNonMovable<false, true>)>);
+STATIC_ASSERT(!is_nothrow_invocable_r_v<NonMovable, decltype(&getConvertsToNonMovable<true, false>)>);
+STATIC_ASSERT(is_nothrow_invocable_r_v<NonMovable, decltype(&getConvertsToNonMovable<true, true>)>);
+#endif // TRANSITION, VSO-1026729
 #endif // _HAS_CXX17