From 7dc7e8e303cf7e5667ceead8fb4320db5f37bf72 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Thu, 27 Mar 2025 17:09:41 +0800
Subject: [PATCH 1/2] Adjust inheritance detection for `enable_view`

---
 stl/inc/optional                              |   5 +-
 stl/inc/xutility                              |  22 +--
 .../P0896R4_ranges_range_machinery/test.cpp   | 143 ++++++++++++++++++
 3 files changed, 155 insertions(+), 15 deletions(-)

diff --git a/stl/inc/optional b/stl/inc/optional
index 14cf3f65127..621d02ff748 100644
--- a/stl/inc/optional
+++ b/stl/inc/optional
@@ -952,8 +952,11 @@ _NODISCARD constexpr bool operator>=(const _Ty1& _Left, const optional<_Ty2>& _R
 }
 
 #if _HAS_CXX20
+template <class _Ty>
+concept _Derived_from_optional = requires(const _Ty& _Obj) { []<class _Uty>(const optional<_Uty>&) {}(_Obj); };
+
 _EXPORT_STD template <class _Ty1, class _Ty2>
-    requires (!_Derived_from_specialization_of<_Ty2, optional>) && three_way_comparable_with<_Ty1, _Ty2>
+    requires (!_Derived_from_optional<_Ty2>) && three_way_comparable_with<_Ty1, _Ty2>
 _NODISCARD constexpr compare_three_way_result_t<_Ty1, _Ty2> operator<=>(const optional<_Ty1>& _Left, const _Ty2& _Right)
     noexcept(noexcept(*_Left <=> _Right)) /* strengthened */ {
     if (_Left) {
diff --git a/stl/inc/xutility b/stl/inc/xutility
index fbce0c9df7c..cd756384c6b 100644
--- a/stl/inc/xutility
+++ b/stl/inc/xutility
@@ -824,14 +824,6 @@ 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 {
 #if defined(__clang__) || defined(__EDG__) // TRANSITION, VSO-1681199
@@ -3424,17 +3416,19 @@ namespace ranges {
 
     _EXPORT_STD struct view_base {};
 
-    template <class _Ty, template <class...> class _Template>
-    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>>
     class view_interface;
 
+    template <class _Ty, class _Uty>
+        requires (!is_same_v<_Ty, view_interface<_Uty>>)
+    void _Strictly_derived_from_view_interface_impl(view_interface<_Uty>*);
+
     _EXPORT_STD template <class _Ty>
-    constexpr bool enable_view =
-        derived_from<_Ty, view_base> || _Strictly_derived_from_specialization_of<_Ty, view_interface>;
+    constexpr bool enable_view = derived_from<_Ty, view_base> || requires {
+        _RANGES _Strictly_derived_from_view_interface_impl<remove_cv_t<_Ty>>(
+            static_cast<remove_cv_t<_Ty>*>(nullptr)); // qualified: avoid ADL, handle incomplete types
+    };
 
     _EXPORT_STD template <class _Ty>
     concept view = range<_Ty> && movable<_Ty> && enable_view<_Ty>;
diff --git a/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp b/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp
index fb4b4d6f98e..83bdb64bc35 100644
--- a/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp
+++ b/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp
@@ -1753,6 +1753,25 @@ static_assert(!ranges::enable_view<const strange_view4&>);
 static_assert(!ranges::enable_view<strange_view4&&>);
 static_assert(!ranges::enable_view<const strange_view4&&>);
 
+// Verify that enable_view<view_interface<T>> is false, i.e., strict derivation is required
+static_assert(!ranges::enable_view<ranges::view_interface<strange_view4>>);
+static_assert(!ranges::enable_view<ranges::view_interface<strange_view5>>);
+
+// Verify that enable_view ignores cv-qualification by default
+template <class T>
+void test_enable_view_cv() { // COMPILE-ONLY
+    static_assert(ranges::enable_view<const T> == ranges::enable_view<T>);
+    static_assert(ranges::enable_view<volatile T> == ranges::enable_view<T>);
+    static_assert(ranges::enable_view<const volatile T> == ranges::enable_view<T>);
+}
+
+void test_enable_view_cv_all() { // COMPILE-ONLY
+    test_enable_view_cv<strange_view4>();
+    test_enable_view_cv<strange_view5>();
+    test_enable_view_cv<ranges::view_interface<strange_view4>>();
+    test_enable_view_cv<ranges::view_interface<strange_view5>>();
+}
+
 // Verify that the derived-from-view_interface mechanism can handle uses of incomplete types whenever possible
 struct incomplet;
 
@@ -1768,6 +1787,80 @@ inline constexpr bool ranges::enable_view<strange_view> = true;
 template <>
 inline constexpr bool ranges::enable_view<strange_view3> = false;
 
+// Test types that satisfy `view` only when being cv-qualified.
+
+struct view_when_const1 : ranges::view_base {
+    view_when_const1(const view_when_const1&&);
+    const view_when_const1& operator=(const view_when_const1&&) const;
+
+    friend void swap(const view_when_const1&, const view_when_const1&);
+
+    int* begin() const;
+    int* end() const;
+};
+
+struct view_when_const2 : ranges::view_interface<view_when_const2> {
+    view_when_const2(const view_when_const2&&);
+    const view_when_const2& operator=(const view_when_const2&&) const;
+
+    friend void swap(const view_when_const2&, const view_when_const2&);
+
+    int* begin() const;
+    int* end() const;
+
+    // avoid checking ranges::view_interface<view_when_const2>::size()
+    void size()       = delete;
+    void size() const = delete;
+};
+
+struct view_when_volatile1 : ranges::view_base {
+    view_when_volatile1(volatile view_when_volatile1&&);
+    volatile view_when_volatile1& operator=(volatile view_when_volatile1&&) volatile;
+
+    friend void swap(volatile view_when_volatile1&, volatile view_when_volatile1&);
+
+    int* begin() volatile;
+    int* end() volatile;
+};
+
+struct view_when_volatile2 : ranges::view_interface<view_when_volatile2> {
+    view_when_volatile2(volatile view_when_volatile2&&);
+    volatile view_when_volatile2& operator=(volatile view_when_volatile2&&) volatile;
+
+    friend void swap(volatile view_when_volatile2&, volatile view_when_volatile2&);
+
+    int* begin() volatile;
+    int* end() volatile;
+
+    // avoid checking ranges::view_interface<view_when_volatile2>::size()
+    void size()       = delete;
+    void size() const = delete;
+};
+
+struct view_when_const_volatile1 : ranges::view_base {
+    view_when_const_volatile1(const volatile view_when_const_volatile1&&);
+    const volatile view_when_const_volatile1& operator=(const volatile view_when_const_volatile1&&) const volatile;
+
+    friend void swap(const volatile view_when_const_volatile1&, const volatile view_when_const_volatile1&);
+
+    int* begin() const volatile;
+    int* end() const volatile;
+};
+
+struct view_when_const_volatile2 : ranges::view_interface<view_when_const_volatile2> {
+    view_when_const_volatile2(const volatile view_when_const_volatile2&&);
+    const volatile view_when_const_volatile2& operator=(const volatile view_when_const_volatile2&&) const volatile;
+
+    friend void swap(const volatile view_when_const_volatile2&, const volatile view_when_const_volatile2&);
+
+    int* begin() const volatile;
+    int* end() const volatile;
+
+    // avoid checking ranges::view_interface<view_when_const_volatile2>::size()
+    void size()       = delete;
+    void size() const = delete;
+};
+
 namespace exhaustive_size_and_view_test {
     template <class Rng, bool IsView = false, class Iterator = invalid_type, class Size = invalid_type>
     constexpr bool test() {
@@ -1869,6 +1962,56 @@ namespace exhaustive_size_and_view_test {
     static_assert(test<strange_view5&, false, I, S>());
     static_assert(test<strange_view5 const, false, CI, S>());
     static_assert(test<strange_view5 const&, false, CI, S>());
+
+    static_assert(test<view_when_const1, false, I, S>());
+    static_assert(test<view_when_const1 const, true, I, S>());
+    static_assert(test<view_when_const1&, false, I, S>());
+    static_assert(test<view_when_const1 const&, false, I, S>());
+
+    static_assert(test<view_when_const2, false, I, S>());
+    static_assert(test<view_when_const2 const, true, I, S>());
+    static_assert(test<view_when_const2&, false, I, S>());
+    static_assert(test<view_when_const2 const&, false, I, S>());
+
+    static_assert(test<view_when_volatile1, false, I, S>());
+    static_assert(test<view_when_volatile1 const, false>());
+    static_assert(test<view_when_volatile1&, false, I, S>());
+    static_assert(test<view_when_volatile1 const&, false>());
+
+    static_assert(test<view_when_volatile2, false, I, S>());
+    static_assert(test<view_when_volatile2 const, false>());
+    static_assert(test<view_when_volatile2&, false, I, S>());
+    static_assert(test<view_when_volatile2 const&, false>());
+
+    static_assert(test<view_when_volatile1 volatile, true, I, S>());
+    static_assert(test<view_when_volatile1 const volatile, false>());
+    static_assert(test<view_when_volatile1 volatile&, false, I, S>());
+    static_assert(test<view_when_volatile1 const volatile&, false>());
+
+    static_assert(test<view_when_volatile2 volatile, true, I, S>());
+    static_assert(test<view_when_volatile2 const volatile, false>());
+    static_assert(test<view_when_volatile2 volatile&, false, I, S>());
+    static_assert(test<view_when_volatile2 const volatile&, false>());
+
+    static_assert(test<view_when_const_volatile1, false, I, S>());
+    static_assert(test<view_when_const_volatile1 const, false, I, S>());
+    static_assert(test<view_when_const_volatile1&, false, I, S>());
+    static_assert(test<view_when_const_volatile1 const&, false, I, S>());
+
+    static_assert(test<view_when_const_volatile2, false, I, S>());
+    static_assert(test<view_when_const_volatile2 const, false, I, S>());
+    static_assert(test<view_when_const_volatile2&, false, I, S>());
+    static_assert(test<view_when_const_volatile2 const&, false, I, S>());
+
+    static_assert(test<view_when_const_volatile1 volatile, false, I, S>());
+    static_assert(test<view_when_const_volatile1 const volatile, true, I, S>());
+    static_assert(test<view_when_const_volatile1 volatile&, false, I, S>());
+    static_assert(test<view_when_const_volatile1 const volatile&, false, I, S>());
+
+    static_assert(test<view_when_const_volatile2 volatile, false, I, S>());
+    static_assert(test<view_when_const_volatile2 const volatile, true, I, S>());
+    static_assert(test<view_when_const_volatile2 volatile&, false, I, S>());
+    static_assert(test<view_when_const_volatile2 const volatile&, false, I, S>());
 } // namespace exhaustive_size_and_view_test
 
 // Validate output_range

From 36c07ed5edd1a54c84addf47a229e66189a24c93 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Fri, 28 Mar 2025 07:50:04 +0800
Subject: [PATCH 2/2] Reported DevCom-10880933, workaround for EDG

---
 stl/inc/optional | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/stl/inc/optional b/stl/inc/optional
index 621d02ff748..8e8e0a4745a 100644
--- a/stl/inc/optional
+++ b/stl/inc/optional
@@ -952,8 +952,16 @@ _NODISCARD constexpr bool operator>=(const _Ty1& _Left, const optional<_Ty2>& _R
 }
 
 #if _HAS_CXX20
+#ifdef __EDG__ // TRANSITION, DevCom-10880933
 template <class _Ty>
-concept _Derived_from_optional = requires(const _Ty& _Obj) { []<class _Uty>(const optional<_Uty>&) {}(_Obj); };
+void _Derived_from_optional_impl(const optional<_Ty>&);
+
+template <class _Ty>
+concept _Derived_from_optional = requires(const _Ty& __obj) { _STD _Derived_from_optional_impl(__obj); };
+#else // ^^^ workaround / no workaround vvv
+template <class _Ty>
+concept _Derived_from_optional = requires(const _Ty& __obj) { []<class _Uty>(const optional<_Uty>&) {}(__obj); };
+#endif // ^^^ no workaround ^^^
 
 _EXPORT_STD template <class _Ty1, class _Ty2>
     requires (!_Derived_from_optional<_Ty2>) && three_way_comparable_with<_Ty1, _Ty2>