Make join_view and join_with_view iterators default-constructible (the forgotten part of P2770R0) (#4264)

stl/inc/ranges

@@ -3809,9 +3809,7 @@ namespace ranges {
             using value_type      = range_value_t<_InnerRng<_Const>>;
             using difference_type = common_type_t<range_difference_t<_Base>, range_difference_t<_InnerRng<_Const>>>;
 
-            // clang-format off
-            _Iterator() requires default_initializable<_OuterIter> = default;
-            // clang-format on
+            _Iterator() = default;
 
             constexpr _Iterator(_Iterator<!_Const> _It)
                 requires _Const && convertible_to<iterator_t<_Vw>, _OuterIter>
@@ -4265,9 +4263,7 @@ namespace ranges {
             using value_type      = common_type_t<iter_value_t<_InnerIter>, iter_value_t<_PatternIter>>;
             using difference_type = _Common_diff_t<_OuterIter, _InnerIter, _PatternIter>;
 
-            // clang-format off
-            _Iterator() requires default_initializable<_OuterIter> = default;
-            // clang-format on
+            _Iterator() = default;
 
             constexpr _Iterator(_Iterator<!_Const> _It)
                 requires _Const && convertible_to<iterator_t<_Vw>, _OuterIter>

tests/libcxx/expected_results.txt

@@ -1202,9 +1202,6 @@ std/ranges/range.adaptors/range.join/range.join.iterator/star.pass.cpp:0 FAIL
 # Not analyzed. constexpr evaluation fails in ranges::swap.
 std/ranges/range.adaptors/range.join/range.join.iterator/iter.swap.pass.cpp:0 FAIL
 
-# Not analyzed. Fails static_assert(std::is_default_constructible_v<JoinIterator>).
-std/ranges/range.adaptors/range.join/range.join.iterator/ctor.default.pass.cpp FAIL
-
 # Not analyzed. constexpr evaluation fails in assert(element_moved == 1).
 std/ranges/range.adaptors/range.lazy.split/ctor.range.pass.cpp:0 FAIL
 std/ranges/range.adaptors/range.split/ctor.range.pass.cpp:0 FAIL

tests/std/tests/P0896R4_views_join/test.cpp

@@ -177,6 +177,16 @@ constexpr bool test_one(Outer&& rng, Expected&& expected) {
             }
         }
 
+        // Also validate that join_view iterators are default-constructible
+        {
+            STATIC_ASSERT(is_default_constructible_v<iterator_t<R>>);
+            [[maybe_unused]] iterator_t<R> i;
+            if constexpr (CanMemberBegin<const R>) {
+                STATIC_ASSERT(is_default_constructible_v<iterator_t<const R>>);
+                [[maybe_unused]] iterator_t<const R> ci;
+            }
+        }
+
         // Validate join_view::end
         static_assert(CanMemberEnd<R>);
         static_assert(CanMemberEnd<const R>

tests/std/tests/P2441R2_views_join_with/test.cpp

@@ -219,6 +219,16 @@ constexpr void test_one(Outer&& rng, Delimiter&& delimiter, Expected&& expected)
         }
     }
 
+    // Also validate that join_with_view iterators are default-constructible
+    {
+        STATIC_ASSERT(is_default_constructible_v<iterator_t<R>>);
+        [[maybe_unused]] iterator_t<R> i;
+        if constexpr (CanMemberBegin<const R>) {
+            STATIC_ASSERT(is_default_constructible_v<iterator_t<const R>>);
+            [[maybe_unused]] iterator_t<const R> ci;
+        }
+    }
+
     // Validate join_with_view::end
     static_assert(CanMemberEnd<R>);
     static_assert(CanMemberEnd<const R>