[libcxx][ranges] removes default_initializable from weakly_incrementable and view

also:

* removes default constructors from predefined iterators
* makes span and string_view views

Partially implements P2325.
Partially resolves LWG3326.

Differential Revision: https://reviews.llvm.org/D102468

libcxx/docs/Cxx2aStatusIssuesStatus.csv

@@ -246,7 +246,7 @@
 "`3323 <https://wg21.link/LWG3323>`__","``*has-tuple-element*``\  helper concept needs ``convertible_to``\ ","Prague","",""
 "`3324 <https://wg21.link/LWG3324>`__","Special-case ``std::strong/weak/partial_order``\  for pointers","Prague","",""
 "`3325 <https://wg21.link/LWG3325>`__","Constrain return type of transformation function for ``transform_view``\ ","Prague","",""
-"`3326 <https://wg21.link/LWG3326>`__","``enable_view``\  has false positives","Prague","",""
+"`3326 <https://wg21.link/LWG3326>`__","``enable_view``\  has false positives","Prague","|In progress|",""
 "`3327 <https://wg21.link/LWG3327>`__","Format alignment specifiers vs. text direction","Prague","|Nothing To Do|",""
 "`3328 <https://wg21.link/LWG3328>`__","Clarify that ``std::string``\  is not good for UTF-8","Prague","",""
 "`3329 <https://wg21.link/LWG3329>`__","``totally_ordered_with``\  both directly and indirectly requires ``common_reference_with``\ ","Prague","|Complete|","13.0"

libcxx/docs/Cxx2aStatusPaperStatus.csv

@@ -194,3 +194,4 @@
 "`P2106 <https://wg21.link/P2106>`__","LWG","Alternative wording for GB315 and GB316","Prague","* *",""
 "`P2116 <https://wg21.link/P2116>`__","LWG","Remove tuple-like protocol support from fixed-extent span","Prague","|Complete|","11.0"
 "`P2231 <https://wg21.link/P2231>`__","LWG","Missing constexpr in std::optional and std::variant","February 2021","|In progress|","13.0"
+"`P2325 <https://wg21.link/P2325>`__","LWG","Views should not be required to be default constructible","June Telecon","|In progress|",""

libcxx/include/__iterator/concepts.h

@@ -71,7 +71,6 @@ concept __signed_integer_like = signed_integral<_Tp>;
 
 template<class _Ip>
 concept weakly_incrementable =
-  default_initializable<_Ip> &&
   movable<_Ip> &&
   requires(_Ip __i) {
     typename iter_difference_t<_Ip>;

libcxx/include/__ranges/concepts.h

@@ -73,7 +73,6 @@ namespace ranges {
   concept view =
     range<_Tp> &&
     movable<_Tp> &&
-    default_initializable<_Tp> &&
     enable_view<_Tp>;
 
   template<class _Range>

libcxx/include/__ranges/enable_view.h

@@ -13,7 +13,6 @@
 #include <__config>
 #include <concepts>
 
-
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif

libcxx/include/iterator

@@ -254,7 +254,6 @@ public:
     typedef void                        reference;
     typedef void                        pointer;
 
-    constexpr back_insert_iterator() noexcept = default; // since C++20
     explicit back_insert_iterator(Container& x);  // constexpr in C++20
     back_insert_iterator& operator=(const typename Container::value_type& value);  // constexpr in C++20
     back_insert_iterator& operator*();  // constexpr in C++20
@@ -278,7 +277,6 @@ public:
     typedef void                         reference;
     typedef void                         pointer;
 
-    constexpr front_insert_iterator() noexcept = default; // since C++20
     explicit front_insert_iterator(Container& x);  // constexpr in C++20
     front_insert_iterator& operator=(const typename Container::value_type& value);  // constexpr in C++20
     front_insert_iterator& operator*();  // constexpr in C++20
@@ -303,7 +301,6 @@ public:
     typedef void                   reference;
     typedef void                   pointer;
 
-    insert_iterator() = default; // since C++20
     insert_iterator(Container& x, typename Container::iterator i);  // constexpr in C++20
     insert_iterator& operator=(const typename Container::value_type& value);  // constexpr in C++20
     insert_iterator& operator*();  // constexpr in C++20
@@ -436,7 +433,6 @@ public:
     typedef traits traits_type;
     typedef basic_ostream<charT,traits> ostream_type;
 
-    constexpr ostream_iterator() noexcept = default; // since C++20
     ostream_iterator(ostream_type& s);
     ostream_iterator(ostream_type& s, const charT* delimiter);
     ostream_iterator(const ostream_iterator& x);
@@ -502,7 +498,6 @@ public:
     typedef basic_streambuf<charT, traits> streambuf_type;
     typedef basic_ostream<charT, traits>   ostream_type;
 
-    constexpr ostreambuf_iterator() noexcept = default; // since C++20
     ostreambuf_iterator(ostream_type& s) noexcept;
     ostreambuf_iterator(streambuf_type* s) noexcept;
     ostreambuf_iterator& operator=(charT c);
@@ -849,9 +844,6 @@ public:
     typedef void reference;
     typedef _Container container_type;
 
-#if _LIBCPP_STD_VER > 17
-    _LIBCPP_INLINE_VISIBILITY constexpr back_insert_iterator() noexcept = default;
-#endif
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 explicit back_insert_iterator(_Container& __x) : container(_VSTD::addressof(__x)) {}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 back_insert_iterator& operator=(const typename _Container::value_type& __value_)
         {container->push_back(__value_); return *this;}
@@ -894,9 +886,6 @@ public:
     typedef void reference;
     typedef _Container container_type;
 
-#if _LIBCPP_STD_VER > 17
-    _LIBCPP_INLINE_VISIBILITY constexpr front_insert_iterator() noexcept = default;
-#endif
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 explicit front_insert_iterator(_Container& __x) : container(_VSTD::addressof(__x)) {}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 front_insert_iterator& operator=(const typename _Container::value_type& __value_)
         {container->push_front(__value_); return *this;}
@@ -927,7 +916,7 @@ class _LIBCPP_TEMPLATE_VIS insert_iterator
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 protected:
     _Container* container;
-    typename _Container::iterator iter;
+    typename _Container::iterator iter; // FIXME: `ranges::iterator_t<Container>` in C++20 mode
 public:
     typedef output_iterator_tag iterator_category;
     typedef void value_type;
@@ -940,9 +929,6 @@ public:
     typedef void reference;
     typedef _Container container_type;
 
-#if _LIBCPP_STD_VER > 17
-    _LIBCPP_INLINE_VISIBILITY insert_iterator() = default;
-#endif
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 insert_iterator(_Container& __x, typename _Container::iterator __i)
         : container(_VSTD::addressof(__x)), iter(__i) {}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 insert_iterator& operator=(const typename _Container::value_type& __value_)
@@ -1061,9 +1047,6 @@ private:
     ostream_type* __out_stream_;
     const char_type* __delim_;
 public:
-#if _LIBCPP_STD_VER > 17
-    _LIBCPP_INLINE_VISIBILITY constexpr ostream_iterator() noexcept = default;
-#endif
     _LIBCPP_INLINE_VISIBILITY ostream_iterator(ostream_type& __s) _NOEXCEPT
         : __out_stream_(_VSTD::addressof(__s)), __delim_(nullptr) {}
     _LIBCPP_INLINE_VISIBILITY ostream_iterator(ostream_type& __s, const _CharT* __delimiter) _NOEXCEPT
@@ -1186,9 +1169,6 @@ public:
 private:
     streambuf_type* __sbuf_;
 public:
-#if _LIBCPP_STD_VER > 17
-    _LIBCPP_INLINE_VISIBILITY constexpr ostreambuf_iterator() noexcept = default;
-#endif
     _LIBCPP_INLINE_VISIBILITY ostreambuf_iterator(ostream_type& __s) _NOEXCEPT
         : __sbuf_(__s.rdbuf()) {}
     _LIBCPP_INLINE_VISIBILITY ostreambuf_iterator(streambuf_type* __s) _NOEXCEPT

libcxx/include/span

@@ -22,6 +22,9 @@ inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max();
 template <class ElementType, size_t Extent = dynamic_extent>
     class span;
 
+template<class ElementType, size_t Extent>
+  inline constexpr bool ranges::enable_view<span<ElementType, Extent>> = true;
+
 template<class ElementType, size_t Extent>
     inline constexpr bool ranges::enable_borrowed_range<span<ElementType, Extent>> = true;
 
@@ -127,6 +130,7 @@ template<class Container>
 #include <__config>
 #include <__debug>
 #include <__ranges/enable_borrowed_range.h>
+#include <__ranges/enable_view.h>
 #include <array>        // for array
 #include <cstddef>      // for byte
 #include <iterator>     // for iterators
@@ -531,6 +535,9 @@ private:
 #if !defined(_LIBCPP_HAS_NO_RANGES)
 template <class _Tp, size_t _Extent>
 inline constexpr bool ranges::enable_borrowed_range<span<_Tp, _Extent> > = true;
+
+template <class _ElementType, size_t _Extent>
+inline constexpr bool ranges::enable_view<span<_ElementType, _Extent>> = true;
 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
 
 //  as_bytes & as_writable_bytes

libcxx/include/string_view

@@ -19,6 +19,9 @@ namespace std {
     template<class charT, class traits = char_traits<charT>>
         class basic_string_view;
 
+    template<class charT, class traits>
+    inline constexpr bool ranges::enable_view<basic_string_view<charT, traits>> = true;
+
     template<class charT, class traits>
     inline constexpr bool ranges::enable_borrowed_range<basic_string_view<charT, traits>> = true;  // C++20
 
@@ -184,6 +187,7 @@ namespace std {
 #include <__config>
 #include <__debug>
 #include <__ranges/enable_borrowed_range.h>
+#include <__ranges/enable_view.h>
 #include <__string>
 #include <algorithm>
 #include <compare>
@@ -654,6 +658,9 @@ private:
 };
 
 #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_RANGES)
+template <class _CharT, class _Traits>
+inline constexpr bool ranges::enable_view<basic_string_view<_CharT, _Traits>> = true;
+
 template <class _CharT, class _Traits>
 inline constexpr bool ranges::enable_borrowed_range<basic_string_view<_CharT, _Traits> > = true;
 #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_RANGES)

libcxx/test/std/containers/views/range_concept_conformance.compile.pass.cpp

@@ -23,13 +23,13 @@ namespace stdr = std::ranges;
 static_assert(std::same_as<stdr::iterator_t<range>, range::iterator>);
 static_assert(stdr::common_range<range>);
 static_assert(stdr::random_access_range<range>);
-static_assert(!stdr::view<range>);
+static_assert(stdr::view<range> && stdr::enable_view<range>);
 static_assert(stdr::sized_range<range>);
 static_assert(stdr::borrowed_range<range>);
 
 static_assert(std::same_as<stdr::iterator_t<range const>, range::iterator>);
 static_assert(stdr::common_range<range const>);
 static_assert(stdr::random_access_range<range const>);
-static_assert(!stdr::view<range const>);
+static_assert(!stdr::view<range const> && !stdr::enable_view<range const>);
 static_assert(stdr::sized_range<range const>);
 static_assert(stdr::borrowed_range<range const>);

libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.winc/subsumption.compile.pass.cpp

@@ -1,33 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: c++03, c++11, c++14, c++17
-// UNSUPPORTED: libcpp-no-concepts
-// UNSUPPORTED: gcc-10
-
-// template<class T>
-// concept weakly_incrementable;
-
-#include <iterator>
-
-#include <concepts>
-
-// clang-format off
-template<std::default_initializable I>
-requires std::movable<I>
-[[nodiscard]] constexpr bool check_subsumption() {
-  return false;
-}
-
-template<std::weakly_incrementable>
-[[nodiscard]] constexpr bool check_subsumption() {
-  return true;
-}
-// clang-format on
-
-static_assert(check_subsumption<int*>());

libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.winc/weakly_incrementable.compile.pass.cpp

@@ -58,10 +58,10 @@ static_assert(!std::weakly_incrementable<floating_difference_type>);
 static_assert(!std::weakly_incrementable<non_const_minus>);
 static_assert(!std::weakly_incrementable<non_integral_minus>);
 static_assert(!std::weakly_incrementable<bad_difference_type_good_minus>);
-static_assert(!std::weakly_incrementable<not_default_initializable>);
 static_assert(!std::weakly_incrementable<not_movable>);
 static_assert(!std::weakly_incrementable<preinc_not_declared>);
 static_assert(!std::weakly_incrementable<postinc_not_declared>);
+static_assert(std::weakly_incrementable<not_default_initializable>);
 static_assert(std::weakly_incrementable<incrementable_with_difference_type>);
 static_assert(std::weakly_incrementable<incrementable_without_difference_type>);
 static_assert(std::weakly_incrementable<difference_type_and_void_minus>);

libcxx/test/std/iterators/predef.iterators/insert.iterators/back.insert.iter.ops/back.insert.iter.cons/default.pass.cpp

@@ -1,38 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: c++03, c++11, c++14, c++17
-
-// <iterator>
-
-// class back_insert_iterator
-
-// constexpr back_insert_iterator() noexcept = default;
-
-#include <iterator>
-#include <vector>
-
-#include "test_macros.h"
-
-struct T { };
-using Container = std::vector<T>;
-
-constexpr bool test() {
-    std::back_insert_iterator<Container> it;
-    (void)it;
-    return true;
-}
-
-int main(int, char**) {
-    ASSERT_NOEXCEPT(std::back_insert_iterator<Container>());
-
-    test();
-    static_assert(test());
-
-    return 0;
-}

libcxx/test/std/iterators/predef.iterators/insert.iterators/front.insert.iter.ops/front.insert.iter.cons/default.pass.cpp

@@ -1,38 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: c++03, c++11, c++14, c++17
-
-// <iterator>
-
-// class front_insert_iterator
-
-// constexpr front_insert_iterator() noexcept = default;
-
-#include <iterator>
-#include <vector>
-
-#include "test_macros.h"
-
-struct T { };
-using Container = std::vector<T>;
-
-constexpr bool test() {
-    std::front_insert_iterator<Container> it;
-    (void)it;
-    return true;
-}
-
-int main(int, char**) {
-    ASSERT_NOEXCEPT(std::front_insert_iterator<Container>());
-
-    test();
-    static_assert(test());
-
-    return 0;
-}

libcxx/test/std/iterators/predef.iterators/insert.iterators/insert.iter.ops/insert.iter.cons/default.pass.cpp

@@ -1,26 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: c++03, c++11, c++14, c++17
-
-// <iterator>
-
-// class insert_iterator
-
-// insert_iterator() = default;
-
-#include <iterator>
-#include <vector>
-
-struct T { };
-using Container = std::vector<T>;
-
-int main(int, char**) {
-    std::insert_iterator<Container> it; (void)it;
-    return 0;
-}

libcxx/test/std/iterators/stream.iterators/ostream.iterator/ostream.iterator.cons.des/default.pass.cpp

@@ -1,42 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: c++03, c++11, c++14, c++17
-
-// <iterator>
-
-// class ostream_iterator
-
-// constexpr ostream_iterator() noexcept = default;
-
-#include <iterator>
-#include <string> // char_traits
-
-#include "test_macros.h"
-
-struct MyTraits : std::char_traits<char> {
-    MyTraits();  // This should not be called.
-};
-
-constexpr bool test() {
-    std::ostream_iterator<int> it;
-    (void)it;
-    std::ostream_iterator<int, char, MyTraits> wit;
-    (void)wit;
-    return true;
-}
-
-int main(int, char**) {
-    ASSERT_NOEXCEPT(std::ostream_iterator<int>());
-    ASSERT_NOEXCEPT(std::ostream_iterator<int, char, MyTraits>());
-
-    test();
-    static_assert(test());
-
-    return 0;
-}

libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/ostreambuf.iter.cons/default.pass.cpp

@@ -1,37 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: c++03, c++11, c++14, c++17
-
-// <iterator>
-
-// class ostreambuf_iterator
-
-// constexpr ostreambuf_iterator() noexcept = default;
-
-#include <iterator>
-
-#include "test_macros.h"
-
-constexpr bool test() {
-    std::ostreambuf_iterator<char> it;
-    (void)it;
-    std::ostreambuf_iterator<wchar_t> wit;
-    (void)wit;
-    return true;
-}
-
-int main(int, char**) {
-    ASSERT_NOEXCEPT(std::ostreambuf_iterator<char>());
-    ASSERT_NOEXCEPT(std::ostreambuf_iterator<wchar_t>());
-
-    test();
-    static_assert(test());
-
-    return 0;
-}

libcxx/test/std/ranges/range.req/range.view/view.compile.pass.cpp

@@ -46,7 +46,7 @@ static_assert(std::ranges::range<NotDefaultInit>);
 static_assert(std::movable<NotDefaultInit>);
 static_assert(!std::default_initializable<NotDefaultInit>);
 static_assert(std::ranges::enable_view<NotDefaultInit>);
-static_assert(!std::ranges::view<NotDefaultInit>);
+static_assert(std::ranges::view<NotDefaultInit>);
 
 // The type would be a view, but it doesn't enable it with enable_view
 struct NotExplicitlyEnabled {

libcxx/test/std/ranges/range.req/range.view/view.subsumption.compile.pass.cpp

@@ -43,11 +43,3 @@ namespace subsume_movable {
   constexpr bool test() { return false; }
   static_assert(test<View>());
 }
-
-namespace subsume_default_initializable {
-  template <std::ranges::view>
-  constexpr bool test() { return true; }
-  template <std::default_initializable>
-  constexpr bool test() { return false; }
-  static_assert(test<View>());
-}

libcxx/test/std/strings/string.view/range_concept_conformance.compile.pass.cpp

@@ -22,13 +22,13 @@ namespace stdr = std::ranges;
 static_assert(std::same_as<stdr::iterator_t<std::string_view>, std::string_view::iterator>);
 static_assert(stdr::common_range<std::string_view>);
 static_assert(stdr::random_access_range<std::string_view>);
-static_assert(!stdr::view<std::string_view>);
+static_assert(stdr::view<std::string_view> && stdr::enable_view<std::string_view>);
 static_assert(stdr::sized_range<std::string_view>);
 static_assert(stdr::borrowed_range<std::string_view>);
 
 static_assert(std::same_as<stdr::iterator_t<std::string_view const>, std::string_view::const_iterator>);
 static_assert(stdr::common_range<std::string_view const>);
 static_assert(stdr::random_access_range<std::string_view const>);
-static_assert(!stdr::view<std::string_view const>); // FIXME: string_view needs to be patched so this is true
+static_assert(!stdr::view<std::string_view const> && !stdr::enable_view<std::string_view const>);
 static_assert(stdr::sized_range<std::string_view const>);
 static_assert(stdr::borrowed_range<std::string_view const>);