Implement P2499R0: `string_view` Range Constructor Should Be `explicit` (#2947)

stl/inc/xstring

@@ -1260,7 +1260,7 @@ public:
             && (!requires {
                 typename remove_reference_t<_Range>::traits_type;
             } || same_as<typename remove_reference_t<_Range>::traits_type, _Traits>))
-    constexpr basic_string_view(_Range&& _Rng) noexcept(
+    constexpr explicit basic_string_view(_Range&& _Rng) noexcept(
         noexcept(_RANGES data(_Rng)) && noexcept(_RANGES size(_Rng))) // strengthened
         : _Mydata(_RANGES data(_Rng)), _Mysize(static_cast<size_t>(_RANGES size(_Rng))) {}
     // clang-format on

stl/inc/yvals_core.h

@@ -316,6 +316,7 @@
 // P2441R2 views::join_with
 // P2442R1 Windowing Range Adaptors: views::chunk, views::slide
 // P2443R1 views::chunk_by
+// P2499R0 string_view Range Constructor Should Be explicit
 // P2549R0 unexpected<E>::error()
 
 // Parallel Algorithms Notes

tests/libcxx/expected_results.txt

@@ -66,6 +66,10 @@ std/utilities/format/format.formatter/format.parse.ctx/begin.pass.cpp FAIL
 std/utilities/format/format.formatter/format.parse.ctx/ctor.pass.cpp FAIL
 std/utilities/format/format.formatter/format.parse.ctx/end.pass.cpp FAIL
 
+# libc++ doesn't yet implement P2499R0
+std/strings/string.view/string.view.cons/from_range.pass.cpp FAIL
+std/strings/string.view/string.view.deduct/range.pass.cpp FAIL
+
 # libc++ doesn't correctly constrain the iterator_traits specialization for common_iterator (https://reviews.llvm.org/D117449)
 std/iterators/predef.iterators/iterators.common/iterator_traits.compile.pass.cpp FAIL
 

tests/libcxx/skipped_tests.txt

@@ -66,6 +66,10 @@ utilities\format\format.formatter\format.parse.ctx\begin.pass.cpp
 utilities\format\format.formatter\format.parse.ctx\ctor.pass.cpp
 utilities\format\format.formatter\format.parse.ctx\end.pass.cpp
 
+# libc++ doesn't yet implement P2499R0
+strings\string.view\string.view.cons\from_range.pass.cpp
+strings\string.view\string.view.deduct\range.pass.cpp
+
 # libc++ doesn't correctly constrain the iterator_traits specialization for common_iterator (https://reviews.llvm.org/D117449)
 iterators\predef.iterators\iterators.common\iterator_traits.compile.pass.cpp
 

tests/std/tests/P0220R1_string_view/test.cpp

@@ -352,7 +352,9 @@ constexpr bool test_case_range_constructor() {
 
     // Also tests some of the constraints:
     static_assert(is_constructible_v<string_view, vector<char>>);
-    static_assert(is_convertible_v<vector<char>, string_view>);
+
+    // P2499R0 string_view Range Constructor Should Be explicit
+    static_assert(!is_convertible_v<vector<char>, string_view>);
 
     static_assert(!is_constructible_v<string_view, deque<char>>); // not contiguous
     static_assert(!is_convertible_v<deque<char>, string_view>);