<barrier>: Fix constructor's exception specification (#5398)

JMazurkiewicz · web-flow · commit 056a3b4bc704 · 2025-04-22T14:57:58.000-07:00
diff --git a/stl/inc/barrier b/stl/inc/barrier
@@ -77,8 +77,8 @@ public:
 
     using arrival_token = _Arrival_token<_Completion_function>;
 
-    constexpr explicit barrier(
-        const ptrdiff_t _Expected, _Completion_function _Fn = _Completion_function()) noexcept /* strengthened */
+    constexpr explicit barrier(const ptrdiff_t _Expected, _Completion_function _Fn = _Completion_function())
+        noexcept(is_nothrow_move_constructible_v<_Completion_function>) // strengthened
         : _Val(_One_then_variadic_args_t{}, _STD move(_Fn), _Expected << _Barrier_value_shift) {
         _STL_VERIFY(_Expected >= 0 && _Expected <= (max) (),
             "Precondition: expected >= 0 and expected <= max() (N4950 [thread.barrier.class]/9)");
diff --git a/tests/std/tests/P1135R6_barrier/test.cpp b/tests/std/tests/P1135R6_barrier/test.cpp
@@ -4,7 +4,10 @@
 #include <atomic>
 #include <barrier>
 #include <cassert>
+#include <cstddef>
+#include <exception>
 #include <thread>
+#include <type_traits>
 #include <utility>
 
 void test() {
@@ -125,12 +128,28 @@ void test_functor_types() {
     };
     std::barrier b1{1, f1{0, 0, 0}};
     b1.arrive_and_wait();
+    static_assert(std::is_nothrow_constructible_v<std::barrier<f1>, std::ptrdiff_t, f1>); // strengthened
 
     std::barrier b2{1, barrier_callback_function};
     b2.arrive_and_wait();
 
     std::barrier b3{1, []() noexcept {}};
     b3.arrive_and_wait();
+
+    struct f2 {
+        void operator()() noexcept {}
+
+        f2() = default;
+        f2(f2&&) {
+            throw std::exception{};
+        }
+    };
+    try {
+        std::barrier b4{1, f2{}};
+        assert(false);
+        static_assert(!std::is_nothrow_constructible_v<std::barrier<f2>, std::ptrdiff_t, f2>);
+    } catch (const std::exception&) {
+    }
 }
 
 int main() {
