[libc++] Tweak how we check constraints on shared_ptr(nullptr_t) (#94996)

This avoids breaking code that should arguably be valid but technically
isn't after enforcing the constraints on shared_ptr's constructors. A
new LWG issue was filed to fix this in the Standard.

This patch applies the expected resolution of this issue to avoid
flip-flopping users whose code should always be considered valid.

See #93071 for more context.

Author: ldionne

libcxx/include/__memory/shared_ptr.h

@@ -404,7 +404,7 @@ struct __shared_ptr_deleter_ctor_reqs {
 };
 
 template <class _Dp, class _Tp>
-using __shared_ptr_nullptr_deleter_ctor_reqs = _And<is_move_constructible<_Dp>, __well_formed_deleter<_Dp, nullptr_t> >;
+using __shared_ptr_nullptr_deleter_ctor_reqs = _And<is_move_constructible<_Dp>, __well_formed_deleter<_Dp, _Tp*> >;
 
 #if defined(_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI)
 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI __attribute__((__trivial_abi__))

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/nullptr_t_deleter.pass.cpp

@@ -32,17 +32,16 @@ int A::count = 0;
 // LWG 3233. Broken requirements for shared_ptr converting constructors
 // https://cplusplus.github.io/LWG/issue3233
 static_assert( std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, test_deleter<int> >::value, "");
-static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, bad_deleter>::value, "");
-static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, no_nullptr_deleter>::value, "");
+static_assert(!std::is_constructible<std::shared_ptr<int>, std::nullptr_t, bad_deleter>::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, no_move_deleter>::value, "");
 
 #if TEST_STD_VER >= 17
-static_assert( std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, test_deleter<int> >::value, "");
+static_assert(std::is_constructible<std::shared_ptr<int[]>, std::nullptr_t, test_deleter<int[]> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, bad_deleter>::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, no_nullptr_deleter>::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, no_move_deleter>::value, "");
 
-static_assert( std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, test_deleter<int> >::value, "");
+static_assert(std::is_constructible<std::shared_ptr<int[5]>, std::nullptr_t, test_deleter<int[5]> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, bad_deleter>::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, no_nullptr_deleter>::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, no_move_deleter>::value, "");

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/nullptr_t_deleter_allocator.pass.cpp

@@ -33,17 +33,21 @@ int A::count = 0;
 // LWG 3233. Broken requirements for shared_ptr converting constructors
 // https://cplusplus.github.io/LWG/issue3233
 static_assert( std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, test_deleter<int>, test_allocator<int> >::value, "");
-static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, bad_deleter, test_allocator<int> >::value, "");
-static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, no_nullptr_deleter, test_allocator<int> >::value, "");
+static_assert(!std::is_constructible<std::shared_ptr<int>, std::nullptr_t, bad_deleter, test_allocator<int> >::value,
+              "");
 static_assert(!std::is_constructible<std::shared_ptr<int>,  std::nullptr_t, no_move_deleter, test_allocator<int> >::value, "");
 
 #if TEST_STD_VER >= 17
-static_assert( std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, test_deleter<int>, test_allocator<int> >::value, "");
+static_assert(
+    std::is_constructible<std::shared_ptr<int[]>, std::nullptr_t, test_deleter<int[]>, test_allocator<int> >::value,
+    "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, bad_deleter, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, no_nullptr_deleter, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[]>,  std::nullptr_t, no_move_deleter, test_allocator<int> >::value, "");
 
-static_assert( std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, test_deleter<int>, test_allocator<int> >::value, "");
+static_assert(
+    std::is_constructible<std::shared_ptr<int[5]>, std::nullptr_t, test_deleter<int[5]>, test_allocator<int> >::value,
+    "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, bad_deleter, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, no_nullptr_deleter, test_allocator<int> >::value, "");
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>,  std::nullptr_t, no_move_deleter, test_allocator<int> >::value, "");

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter.pass.cpp

@@ -115,6 +115,14 @@ int main(int, char**)
     }
 #endif // TEST_STD_VER >= 11
 
+#if TEST_STD_VER >= 14
+    {
+      // See https://github.com/llvm/llvm-project/pull/93071#issuecomment-2158494851
+      auto deleter = [](auto pointer) { delete pointer; };
+      std::shared_ptr<int> p(new int, deleter);
+    }
+#endif
+
   test_function_type();
   return 0;
 }

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter_allocator.pass.cpp

@@ -165,5 +165,13 @@ int main(int, char**)
                                              test_allocator<Derived[4]> >::value, "");
     }
 
+#if TEST_STD_VER >= 14
+    {
+      // See https://github.com/llvm/llvm-project/pull/93071#issuecomment-2158494851
+      auto deleter = [](auto pointer) { delete pointer; };
+      std::shared_ptr<int> p(new int, deleter, std::allocator<int>());
+    }
+#endif
+
   return 0;
 }