From 794563c56afac91b7b2f3a9a7f13075d5bed70c2 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Mon, 5 Dec 2022 11:09:45 +0800
Subject: [PATCH 1/5] Test coverage for LWG-3746

---
 tests/std/tests/P1614R2_spaceship/test.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tests/std/tests/P1614R2_spaceship/test.cpp b/tests/std/tests/P1614R2_spaceship/test.cpp
index daeccca953..3b6dc63338 100644
--- a/tests/std/tests/P1614R2_spaceship/test.cpp
+++ b/tests/std/tests/P1614R2_spaceship/test.cpp
@@ -290,6 +290,9 @@ constexpr bool tuple_like_test() {
     return true;
 }
 
+template <class T>
+struct derived_optional : std::optional<T> {};
+
 template <auto SmallVal, decltype(SmallVal) EqualVal, decltype(EqualVal) LargeVal>
 constexpr bool optional_test() {
     using ReturnType = std::compare_three_way_result_t<decltype(SmallVal)>;
@@ -313,6 +316,13 @@ constexpr bool optional_test() {
 
         assert(spaceship_test<ReturnType>(o1, EqualVal, LargeVal));
     }
+    {
+        constexpr std::optional o1(SmallVal);
+        constexpr derived_optional<decltype(SmallVal)> derived1{std::optional(SmallVal)};
+        constexpr derived_optional<decltype(SmallVal)> derived2{std::optional(LargeVal)};
+
+        assert(spaceship_test<ReturnType>(o1, derived1, derived2));
+    }
     {
         constexpr std::optional<decltype(SmallVal)> o1(std::nullopt);
         constexpr std::optional o2(LargeVal);

From 8e4c5e3d8c12310fc93822363f0f0d4c320d0cee Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Mon, 5 Dec 2022 11:10:49 +0800
Subject: [PATCH 2/5] Implement LWG-3746

---
 stl/inc/optional |  2 +-
 stl/inc/xutility | 20 +++++++++++---------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/stl/inc/optional b/stl/inc/optional
index 6b88502722..a86eaa23be 100644
--- a/stl/inc/optional
+++ b/stl/inc/optional
@@ -926,7 +926,7 @@ _NODISCARD constexpr bool operator>=(const _Ty1& _Left, const optional<_Ty2>& _R
 #ifdef __cpp_lib_concepts
 // clang-format off
 _EXPORT_STD template <class _Ty1, class _Ty2>
-    requires (!_Is_specialization_v<_Ty2, optional>)
+    requires (!_Derived_from_specialization_of<_Ty2, optional>)
         && three_way_comparable_with<_Ty1, _Ty2>
 _NODISCARD constexpr compare_three_way_result_t<_Ty1, _Ty2>
     operator<=>(const optional<_Ty1>& _Left, const _Ty2& _Right)
diff --git a/stl/inc/xutility b/stl/inc/xutility
index b8a210a37a..180845258f 100644
--- a/stl/inc/xutility
+++ b/stl/inc/xutility
@@ -400,6 +400,14 @@ using _Algorithm_int_t = conditional_t<is_integral_v<_Ty>, _Ty, ptrdiff_t>;
 template <class _Ty>
 concept _Destructible_object = is_object_v<_Ty> && destructible<_Ty>;
 
+template <template <class...> class _Template, class... _Args>
+void _Derived_from_specialization_impl(const _Template<_Args...>&);
+
+template <class _Ty, template <class...> class _Template>
+concept _Derived_from_specialization_of = requires(const _Ty& _Obj) {
+    _STD _Derived_from_specialization_impl<_Template>(_Obj); // qualified: avoid ADL, handle incomplete types
+};
+
 namespace ranges {
     namespace _Iter_move {
         void iter_move(); // Block unqualified name lookup
@@ -2916,15 +2924,9 @@ namespace ranges {
 
     _EXPORT_STD struct view_base {};
 
-    template <template <class...> class _Template, class... _Args>
-    void _Derived_from_specialization_impl(const _Template<_Args...>&);
-
     template <class _Ty, template <class...> class _Template>
-    concept _Derived_from_specialization_of =
-        is_object_v<_Ty> && requires(const _Ty& _Obj) {
-                                _RANGES _Derived_from_specialization_impl<_Template>(
-                                    _Obj); // qualified: avoid ADL, handle incompletable types
-                            };
+    concept _Strictly_derived_from_specialization_of =
+        is_object_v<_Ty> && _Derived_from_specialization_of<_Ty, _Template>;
 
     _EXPORT_STD template <class _Derived>
         requires is_class_v<_Derived> && same_as<_Derived, remove_cv_t<_Derived>>
@@ -2932,7 +2934,7 @@ namespace ranges {
 
     _EXPORT_STD template <class _Ty>
     inline constexpr bool enable_view =
-        derived_from<_Ty, view_base> || _Derived_from_specialization_of<_Ty, view_interface>;
+        derived_from<_Ty, view_base> || _Strictly_derived_from_specialization_of<_Ty, view_interface>;
 
     _EXPORT_STD template <class _Ty>
     concept view = range<_Ty> && movable<_Ty> && enable_view<_Ty>;

From de41462b2fd2fcb61bf3379b74367f38ca71a363 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Mon, 5 Dec 2022 14:34:03 +0800
Subject: [PATCH 3/5] Change the test

---
 tests/std/tests/P1614R2_spaceship/test.cpp | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/tests/std/tests/P1614R2_spaceship/test.cpp b/tests/std/tests/P1614R2_spaceship/test.cpp
index 3b6dc63338..8d33b1cb0e 100644
--- a/tests/std/tests/P1614R2_spaceship/test.cpp
+++ b/tests/std/tests/P1614R2_spaceship/test.cpp
@@ -291,7 +291,9 @@ constexpr bool tuple_like_test() {
 }
 
 template <class T>
-struct derived_optional : std::optional<T> {};
+struct derived_optional : std::optional<T> {
+    friend bool operator==(const derived_optional&, const derived_optional&) = default;
+};
 
 template <auto SmallVal, decltype(SmallVal) EqualVal, decltype(EqualVal) LargeVal>
 constexpr bool optional_test() {
@@ -311,16 +313,13 @@ constexpr bool optional_test() {
 
         assert(spaceship_test<ReturnType>(o1, o1_equal, o2));
     }
-    {
-        constexpr std::optional o1(SmallVal);
-
-        assert(spaceship_test<ReturnType>(o1, EqualVal, LargeVal));
-    }
     {
         constexpr std::optional o1(SmallVal);
         constexpr derived_optional<decltype(SmallVal)> derived1{std::optional(SmallVal)};
         constexpr derived_optional<decltype(SmallVal)> derived2{std::optional(LargeVal)};
 
+        static_assert(!std::three_way_comparable<derived_optional<decltype(SmallVal)>>);
+
         assert(spaceship_test<ReturnType>(o1, derived1, derived2));
     }
     {

From cef1fcff5624310f1a1879cfb78b7f7415017519 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Mon, 5 Dec 2022 14:37:51 +0800
Subject: [PATCH 4/5] Restore an assertion

---
 tests/std/tests/P1614R2_spaceship/test.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tests/std/tests/P1614R2_spaceship/test.cpp b/tests/std/tests/P1614R2_spaceship/test.cpp
index 8d33b1cb0e..46303176e3 100644
--- a/tests/std/tests/P1614R2_spaceship/test.cpp
+++ b/tests/std/tests/P1614R2_spaceship/test.cpp
@@ -320,6 +320,7 @@ constexpr bool optional_test() {
 
         static_assert(!std::three_way_comparable<derived_optional<decltype(SmallVal)>>);
 
+        assert(spaceship_test<ReturnType>(o1, EqualVal, LargeVal));
         assert(spaceship_test<ReturnType>(o1, derived1, derived2));
     }
     {

From 25c849cb47702b81d0d0461cad38ed42d2bfb0df Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Mon, 5 Dec 2022 14:56:07 +0800
Subject: [PATCH 5/5] Clang-format

---
 stl/inc/xutility | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/stl/inc/xutility b/stl/inc/xutility
index 180845258f..f32800f13b 100644
--- a/stl/inc/xutility
+++ b/stl/inc/xutility
@@ -404,9 +404,10 @@ template <template <class...> class _Template, class... _Args>
 void _Derived_from_specialization_impl(const _Template<_Args...>&);
 
 template <class _Ty, template <class...> class _Template>
-concept _Derived_from_specialization_of = requires(const _Ty& _Obj) {
-    _STD _Derived_from_specialization_impl<_Template>(_Obj); // qualified: avoid ADL, handle incomplete types
-};
+concept _Derived_from_specialization_of =
+    requires(const _Ty& _Obj) {
+        _STD _Derived_from_specialization_impl<_Template>(_Obj); // qualified: avoid ADL, handle incomplete types
+    };
 
 namespace ranges {
     namespace _Iter_move {