Implement LWG-3900 The allocator_arg_t overloads of generator::promise_type::operator new should not be constrained (#5150)

Co-authored-by: Casey Carter <[email protected]>

Author: frederick-vs-ja

stl/inc/generator

@@ -110,16 +110,18 @@ namespace _Gen_detail {
         }
 
         template <class _Alloc2, class... _Args>
-            requires convertible_to<const _Alloc2&, _Proto_allocator>
         _NODISCARD_RAW_PTR_ALLOC static void* operator new(
             const size_t _Size, allocator_arg_t, const _Alloc2& _Al, const _Args&...) {
+            static_assert(convertible_to<const _Alloc2&, _Proto_allocator>,
+                "Allocator argument must be convertible to the allocator type (N5001 [coro.generator.promise]/18)");
             return _Allocate(static_cast<_Alloc>(static_cast<_Proto_allocator>(_Al)), _Size);
         }
 
         template <class _This, class _Alloc2, class... _Args>
-            requires convertible_to<const _Alloc2&, _Proto_allocator>
         _NODISCARD_RAW_PTR_ALLOC static void* operator new(
             const size_t _Size, const _This&, allocator_arg_t, const _Alloc2& _Al, const _Args&...) {
+            static_assert(convertible_to<const _Alloc2&, _Proto_allocator>,
+                "Allocator argument must be convertible to the allocator type (N5001 [coro.generator.promise]/18)");
             return _Allocate(static_cast<_Alloc>(static_cast<_Proto_allocator>(_Al)), _Size);
         }
 

tests/std/tests/P2502R2_generator_promise/test.cpp

@@ -78,20 +78,18 @@ void test_operator_new(typename Gen::promise_type& p, const Alloc2& alloc2 = {})
     }
 
     // Test 'operator new(size_t, allocator_arg_t, const Alloc2&, const Args&...)'
-    constexpr bool has_op_new2 = HasOperatorNew<Promise, size_t, allocator_arg_t, const Alloc2&, int, int>;
-    static_assert(has_op_new2 == (same_as<Alloc, void> || convertible_to<const Alloc2&, Alloc>) );
-    if constexpr (has_op_new2) {
+    // This operator new is unconstrained.
+    if constexpr (same_as<Alloc, void> || convertible_to<const Alloc2&, Alloc>) {
         const size_t size = __STDCPP_DEFAULT_NEW_ALIGNMENT__;
         void* const mem   = p.operator new(size, allocator_arg, alloc2, 0, 0);
         assert(reinterpret_cast<uintptr_t>(mem) % __STDCPP_DEFAULT_NEW_ALIGNMENT__ == 0);
         p.operator delete(mem, size);
     }
 
     // Test 'operator new(size_t, const This&, allocator_arg_t, const Alloc2&, const Args&...)'
+    // This operator new is unconstrained.
     struct S {};
-    constexpr bool has_op_new3 = HasOperatorNew<Promise, size_t, const S&, allocator_arg_t, const Alloc2&, int, int>;
-    static_assert(has_op_new3 == (same_as<Alloc, void> || convertible_to<const Alloc2&, Alloc>) );
-    if constexpr (has_op_new3) {
+    if constexpr (same_as<Alloc, void> || convertible_to<const Alloc2&, Alloc>) {
         const size_t size = __STDCPP_DEFAULT_NEW_ALIGNMENT__;
         const S s;
         void* const mem = p.operator new(size, s, allocator_arg, alloc2, 0, 0);