Workaround for LLVM-46269 constrained destructor ordering (#2630)

stl/inc/iterator

@@ -618,15 +618,14 @@ public:
         }
     }
 
-    // clang-format off
-    constexpr ~_Variantish() requires is_trivially_destructible_v<_It> && is_trivially_destructible_v<_Se> = default;
-    // clang-format on
-
     constexpr ~_Variantish() {
         _Raw_clear();
     }
 
+    // TRANSITION, LLVM-46269, destructor order is significant
     // clang-format off
+    constexpr ~_Variantish() requires is_trivially_destructible_v<_It> && is_trivially_destructible_v<_Se> = default;
+
     constexpr _Variantish& operator=(const _Variantish&) requires is_trivially_destructible_v<_It>
         && is_trivially_destructible_v<_Se>
         && is_trivially_copy_constructible_v<_It>

stl/inc/ranges

@@ -271,17 +271,16 @@ namespace ranges {
             is_nothrow_constructible_v<_Ty, _Types...>) // strengthened
             : _Val(_STD forward<_Types>(_Args)...), _Engaged{true} {}
 
-        // clang-format off
-        ~_Copyable_box() requires is_trivially_destructible_v<_Ty> = default;
-        // clang-format on
-
         constexpr ~_Copyable_box() {
             if (_Engaged) {
                 _Val.~_Ty();
             }
         }
 
+        // TRANSITION, LLVM-46269, destructor order is significant
         // clang-format off
+        ~_Copyable_box() requires is_trivially_destructible_v<_Ty> = default;
+
         _Copyable_box(const _Copyable_box&) requires is_trivially_copy_constructible_v<_Ty> = default;
         // clang-format on
 
@@ -474,17 +473,16 @@ namespace ranges {
     public:
         constexpr _Defaultabox() noexcept {}
 
-        // clang-format off
-        ~_Defaultabox() requires is_trivially_destructible_v<_Ty> = default;
-        // clang-format on
-
         constexpr ~_Defaultabox() {
             if (_Engaged) {
                 _Val.~_Ty();
             }
         }
 
+        // TRANSITION, LLVM-46269, destructor order is significant
         // clang-format off
+        ~_Defaultabox() requires is_trivially_destructible_v<_Ty> = default;
+
         _Defaultabox(const _Defaultabox&)
             requires copy_constructible<_Ty> && is_trivially_copy_constructible_v<_Ty> = default;
         // clang-format on
@@ -693,6 +691,7 @@ namespace ranges {
             }
         }
 
+        // TRANSITION, LLVM-46269, destructor order is significant
         // clang-format off
         ~_Non_propagating_cache() requires is_trivially_destructible_v<_Ty> = default;
         // clang-format on

tests/std/tests/P0896R4_common_iterator/test.cpp

@@ -311,6 +311,29 @@ constexpr bool test_lwg_3574() {
     return true;
 }
 
+// Validate that _Variantish works when fed with a non-trivially-destructible type
+void test_non_trivially_destructible_type() { // COMPILE-ONLY
+    struct non_trivially_destructible_input_iterator {
+        using difference_type = int;
+        using value_type      = int;
+
+        ~non_trivially_destructible_input_iterator() {}
+
+        non_trivially_destructible_input_iterator& operator++() {
+            return *this;
+        }
+        void operator++(int) {}
+        int operator*() const {
+            return 0;
+        }
+        bool operator==(default_sentinel_t) const {
+            return true;
+        }
+    };
+
+    common_iterator<non_trivially_destructible_input_iterator, default_sentinel_t> it;
+}
+
 int main() {
     with_writable_iterators<instantiator, P>::call();
     static_assert(with_writable_iterators<instantiator, P>::call());

tests/std/tests/P0896R4_views_join/test.cpp

@@ -471,6 +471,38 @@ struct Immovable {
     Immovable& operator=(Immovable&&) = delete;
 };
 
+// Validate that the _Defaultabox primary template works when fed with a non-trivially-destructible type
+void test_non_trivially_destructible_type() { // COMPILE-ONLY
+    struct non_trivially_destructible_input_iterator {
+        using difference_type = int;
+        using value_type      = int;
+
+        ~non_trivially_destructible_input_iterator() {}
+
+        // To test the correct specialization of _Defaultabox, this type must not be default constructible.
+        non_trivially_destructible_input_iterator() = delete;
+
+        non_trivially_destructible_input_iterator& operator++() {
+            return *this;
+        }
+        void operator++(int) {}
+        int operator*() const {
+            return 0;
+        }
+        bool operator==(default_sentinel_t) const {
+            return true;
+        }
+    };
+
+    using Inner = ranges::subrange<non_trivially_destructible_input_iterator, default_sentinel_t>;
+
+    auto r = views::empty<Inner> | views::join;
+    (void) r.begin();
+
+    // Also validate _Non_propagating_cache
+    auto r2 = views::empty<Inner> | views::transform([](Inner& r) { return r; }) | views::join;
+}
+
 int main() {
     // Validate views
     constexpr string_view expected = "Hello World!"sv;

tests/std/tests/P0896R4_views_single/test.cpp

@@ -139,6 +139,20 @@ static_assert(same_as<ranges::single_view<const char*>, decltype(views::single("
 void double_function(double);
 static_assert(same_as<ranges::single_view<void (*)(double)>, decltype(views::single(double_function))>);
 
+// Validate that the _Copyable_box primary template works when fed with a non-trivially-destructible type
+void test_non_trivially_destructible_type() { // COMPILE-ONLY
+    struct non_trivially_destructible {
+        non_trivially_destructible() = default;
+        ~non_trivially_destructible() {}
+
+        // To test the correct specialization of _Copyable_box, this type must not be copy assignable.
+        non_trivially_destructible(const non_trivially_destructible&) = default;
+        non_trivially_destructible& operator=(const non_trivially_destructible&) = delete;
+    };
+
+    (void) views::single(non_trivially_destructible{});
+}
+
 int main() {
     static_assert(test_one_type(42, 42));
     test_one_type(42, 42);