[PATCH 5/5] libstdc++: Implement new views::split as per P2210

[Patrick Palka <ppalka@redhat.com>]

This implements the new views::split as specified by P2210R2 "Superior
string splitting".

libstdc++-v3/ChangeLog:

	* include/std/ranges (__non_propagating_cache::operator bool):
	Define.
	(split_view): Define as per P2210.
	(views::__detail::__can_split_view): Define.
	(views::_Split, views::Split): Define.
	* testsuite/std/ranges/adaptors/100577.cc (test01, test02):
	Test views::split.
	* testsuite/std/ranges/adaptors/split.cc: New test.
	* testsuite/std/ranges/p2325.cc (test08a): New test.
	* testsuite/std/ranges/p2367.cc (test01): Test views::split.
---
 libstdc++-v3/include/std/ranges               | 205 ++++++++++++++++++
 .../testsuite/std/ranges/adaptors/100577.cc   |  16 +-
 .../testsuite/std/ranges/adaptors/split.cc    | 196 +++++++++++++++++
 libstdc++-v3/testsuite/std/ranges/p2325.cc    |  14 ++
 libstdc++-v3/testsuite/std/ranges/p2367.cc    |   1 +
 5 files changed, 430 insertions(+), 2 deletions(-)
 create mode 100644 libstdc++-v3/testsuite/std/ranges/adaptors/split.cc

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 78562924bee..42278f128b8 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1195,6 +1195,10 @@ namespace views::__adaptor
 	  return *this;
 	}
 
+	constexpr explicit
+	operator bool() const noexcept
+	{ return this->_M_is_engaged(); }
+
 	constexpr _Tp&
 	operator*() noexcept
 	{ return this->_M_get(); }
@@ -3278,6 +3282,207 @@ namespace views::__adaptor
     inline constexpr _LazySplit lazy_split;
   } // namespace views
 
+  template<forward_range _Vp, forward_range _Pattern>
+    requires view<_Vp> && view<_Pattern>
+      && indirectly_comparable<iterator_t<_Vp>, iterator_t<_Pattern>,
+			       ranges::equal_to>
+  class split_view : public view_interface<split_view<_Vp, _Pattern>>
+  {
+  private:
+    _Pattern _M_pattern = _Pattern();
+    __detail::__non_propagating_cache<subrange<iterator_t<_Vp>>> _M_cached_begin;
+    _Vp _M_base = _Vp();
+
+    struct _Iterator;
+    struct _Sentinel;
+
+  public:
+    split_view() requires (default_initializable<_Vp>
+			   && default_initializable<_Pattern>)
+      = default;
+
+    constexpr
+    split_view(_Vp __base, _Pattern __pattern)
+      : _M_pattern(std::move(__pattern)),
+	_M_base(std::move(__base))
+    { }
+
+    template<forward_range _Range>
+      requires constructible_from<_Vp, views::all_t<_Range>>
+	&& constructible_from<_Pattern, single_view<range_value_t<_Range>>>
+    constexpr
+    split_view(_Range&& __r, range_value_t<_Range> __e)
+      : _M_pattern(views::single(__e)),
+	_M_base(views::all(std::forward<_Range>(__r)))
+    { }
+
+    constexpr _Vp
+    base() const& requires copyable<_Vp>
+    { return _M_base; }
+
+    constexpr _Vp
+    base() &&
+    { return std::move(_M_base); }
+
+    constexpr _Iterator
+    begin()
+    {
+      if (!_M_cached_begin)
+	_M_cached_begin = _M_find_next(ranges::begin(_M_base));
+      return {this, ranges::begin(_M_base), *_M_cached_begin};
+    }
+
+    constexpr auto
+    end()
+    {
+      if constexpr (common_range<_Vp>)
+	return _Iterator{this, ranges::end(_M_base), {}};
+      else
+	return _Sentinel{this};
+    }
+
+    constexpr subrange<iterator_t<_Vp>>
+    _M_find_next(iterator_t<_Vp> __it)
+    {
+      auto [__b, __e] = ranges::search(subrange(__it, ranges::end(_M_base)), _M_pattern);
+      if (__b != ranges::end(_M_base) && ranges::empty(_M_pattern))
+	{
+	  ++__b;
+	  ++__e;
+	}
+      return {__b, __e};
+    }
+
+  private:
+    struct _Iterator
+    {
+    private:
+      split_view* _M_parent = nullptr;
+      iterator_t<_Vp> _M_cur = iterator_t<_Vp>();
+      subrange<iterator_t<_Vp>> _M_next = subrange<iterator_t<_Vp>>();
+      bool _M_trailing_empty = false;
+
+    public:
+      using iterator_concept = forward_iterator_tag;
+      using iterator_category = input_iterator_tag;
+      using value_type = subrange<iterator_t<_Vp>>;
+      using difference_type = range_difference_t<_Vp>;
+
+      _Iterator() requires default_initializable<iterator_t<_Vp>> = default;
+
+      constexpr
+      _Iterator(split_view* __parent,
+		iterator_t<_Vp> __current,
+		subrange<iterator_t<_Vp>> __next)
+	: _M_parent(__parent),
+	  _M_cur(std::move(__current)),
+	  _M_next(std::move(__next))
+      { }
+
+      constexpr iterator_t<_Vp>
+      base() const
+      { return _M_cur; }
+
+      constexpr value_type
+      operator*() const
+      { return {_M_cur, _M_next.begin()}; }
+
+      constexpr _Iterator&
+      operator++()
+      {
+	_M_cur = _M_next.begin();
+	if (_M_cur != ranges::end(_M_parent->_M_base))
+	  {
+	    _M_cur = _M_next.end();
+	    if (_M_cur == ranges::end(_M_parent->_M_base))
+	      {
+		_M_trailing_empty = true;
+		_M_next = {_M_cur, _M_cur};
+	      }
+	    else
+	      _M_next = _M_parent->_M_find_next(_M_cur);
+	  }
+	else
+	  _M_trailing_empty = false;
+	return *this;
+      }
+
+      constexpr _Iterator
+      operator++(int)
+      {
+	auto __tmp = *this;
+	++*this;
+	return __tmp;
+      }
+
+      friend constexpr bool
+      operator==(const _Iterator& __x, const _Iterator& __y)
+      {
+	return __x._M_cur == __y._M_cur
+	  && __x._M_trailing_empty == __y._M_trailing_empty;
+      }
+
+      friend struct _Sentinel;
+    };
+
+    struct _Sentinel
+    {
+    private:
+      sentinel_t<_Vp> _M_end = sentinel_t<_Vp>();
+
+      constexpr bool
+      _M_equal(const _Iterator& __x) const
+      { return __x._M_cur == _M_end && !__x._M_trailing_empty; }
+
+    public:
+      constexpr explicit
+      _Sentinel(split_view* __parent)
+	: _M_end(ranges::end(__parent->_M_base))
+      { }
+
+      friend constexpr bool
+      operator==(const _Iterator& __x, const _Sentinel& __y)
+      { return __y._M_equal(__x); }
+    };
+  };
+
+  template<typename _Range, typename _Pattern>
+    split_view(_Range&&, _Pattern&&)
+      -> split_view<views::all_t<_Range>, views::all_t<_Pattern>>;
+
+  template<forward_range _Range>
+    split_view(_Range&&, range_value_t<_Range>)
+      -> split_view<views::all_t<_Range>, single_view<range_value_t<_Range>>>;
+
+  namespace views
+  {
+    namespace __detail
+    {
+      template<typename _Range, typename _Pattern>
+	concept __can_split_view
+	  = requires { split_view(std::declval<_Range>(), std::declval<_Pattern>()); };
+    } // namespace __detail
+
+    struct _Split : __adaptor::_RangeAdaptor<_Split>
+    {
+      template<viewable_range _Range, typename _Pattern>
+	requires __detail::__can_split_view<_Range, _Pattern>
+	constexpr auto
+	operator()(_Range&& __r, _Pattern&& __f) const
+	{
+	  return split_view(std::forward<_Range>(__r), std::forward<_Pattern>(__f));
+	}
+
+      using _RangeAdaptor<_Split>::operator();
+      static constexpr int _S_arity = 2;
+      template<typename _Pattern>
+	static constexpr bool _S_has_simple_extra_args
+	  = _LazySplit::_S_has_simple_extra_args<_Pattern>;
+    };
+
+    inline constexpr _Split split;
+  } // namespace views
+
   namespace views
   {
     struct _Counted
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc
index 5ef7f3f59a7..81f2a62cfaa 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/100577.cc
@@ -42,8 +42,6 @@ test01()
   static_assert(__adaptor_has_simple_extra_args<decltype(views::lazy_split), char>);
   static_assert(!__adaptor_has_simple_extra_args<decltype(views::lazy_split), std::string>);
 
-  // Verify all adaptor closures except for views::lazy_split(pattern) have a simple
-  // operator().
   using views::__adaptor::__closure_has_simple_call_op;
   __closure_has_simple_call_op auto a00 = views::all;
   __closure_has_simple_call_op auto a01 = views::transform(std::identity{});
@@ -57,6 +55,7 @@ test01()
   __closure_has_simple_call_op auto a09 = views::reverse;
   __closure_has_simple_call_op auto a10 = views::keys;
   __closure_has_simple_call_op auto a11 = views::lazy_split(' ');
+  __closure_has_simple_call_op auto a11a = views::split(' ');
   // Verify composition of simple closures is simple.
   __closure_has_simple_call_op auto b
     = (a00 | a01) | (a02 | a03) | (a04 | a05 | a06) | (a07 | a08 | a09 | a10) | a11;
@@ -67,6 +66,12 @@ test01()
   static_assert(!__closure_has_simple_call_op<decltype(a12)>);
   static_assert(!__closure_has_simple_call_op<decltype(a12 | a00)>);
   static_assert(!__closure_has_simple_call_op<decltype(a00 | a12)>);
+
+  // Likewise views::split(non_view_range).
+  auto a12a = views::split(s);
+  static_assert(!__closure_has_simple_call_op<decltype(a12a)>);
+  static_assert(!__closure_has_simple_call_op<decltype(a12a | a00)>);
+  static_assert(!__closure_has_simple_call_op<decltype(a00 | a12a)>);
 }
 
 void
@@ -98,6 +103,13 @@ test02()
   auto a1 = a0 | views::all;
   a1(x); // { dg-error "no match" }
 
+  views::lazy_split(badarg)(x); // { dg-error "deleted function" }
+  (views::lazy_split(badarg) | views::all)(x); // { dg-error "deleted function" }
+  auto a0a = views::split(badarg);
+  a0a(x); // { dg-error "no match" };
+  auto a1a = a0a | views::all;
+  a1a(x); // { dg-error "no match" }
+
   views::take(badarg)(x); // { dg-error "deleted" }
   views::drop(badarg)(x); // { dg-error "deleted" }
   (views::take(badarg) | views::all)(x); // { dg-error "deleted" }
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/split.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/split.cc
new file mode 100644
index 00000000000..9e6726cd07f
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/split.cc
@@ -0,0 +1,196 @@
+// Copyright (C) 2020-2021 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <ranges>
+#include <string>
+#include <string_view>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using __gnu_test::test_range;
+using __gnu_test::forward_iterator_wrapper;
+using __gnu_test::input_iterator_wrapper;
+
+namespace ranges = std::ranges;
+namespace views = std::ranges::views;
+
+using namespace std::literals;
+
+void
+test01()
+{
+  auto from_chars = [] (auto v) {
+    return std::stoi(std::string(v.data(), v.data() + v.size()));
+  };
+  auto ints = "1.2.3.4"sv
+    | views::split('.')
+    | views::transform(from_chars);
+  VERIFY( ranges::equal(ints, (int[]){1,2,3,4}) );
+}
+
+// The following testcases were adapted from lazy_split.cc.
+namespace from_lazy_split_cc
+{
+void
+test01()
+{
+  auto x = "the  quick  brown  fox"sv;
+  auto p = std::string{"  "};
+  auto v = x | views::split(views::all(p)); // views::all is needed here after P2281.
+  auto i = v.begin();
+  VERIFY( ranges::equal(*i++, "the"sv) );
+  VERIFY( ranges::equal(*i++, "quick"sv) );
+  VERIFY( ranges::equal(*i++, "brown"sv) );
+  VERIFY( ranges::equal(*i++, "fox"sv) );
+  VERIFY( i == v.end() );
+}
+
+void
+test02()
+{
+  auto x = "the quick brown fox"sv;
+  auto v = x | views::split(' ');
+  auto i = v.begin();
+  VERIFY( ranges::equal(*i++, "the"sv) );
+  VERIFY( ranges::equal(*i++, "quick"sv) );
+  VERIFY( ranges::equal(*i++, "brown"sv) );
+  VERIFY( ranges::equal(*i++, "fox"sv) );
+  VERIFY( i == v.end() );
+}
+
+void
+test03()
+{
+  char x[] = "the quick brown fox";
+  test_range<char, forward_iterator_wrapper> rx(x, x+sizeof(x)-1);
+  auto v = rx | views::split(' ');
+  auto i = v.begin();
+  VERIFY( ranges::equal(*i++, "the"sv) );
+  VERIFY( ranges::equal(*i++, "quick"sv) );
+  VERIFY( ranges::equal(*i++, "brown"sv) );
+  VERIFY( ranges::equal(*i++, "fox"sv) );
+  VERIFY( i == v.end() );
+}
+
+void
+test04()
+{
+  auto x = "the  quick  brown  fox"sv;
+  std::initializer_list<char> p = {' ', ' '};
+  static_assert(!ranges::view<decltype(p)>);
+  static_assert(std::same_as<decltype(p | views::all),
+			     ranges::ref_view<decltype(p)>>);
+  auto v = x | views::split(views::all(p)); // views::all is needed here after P2281.
+  auto i = v.begin();
+  VERIFY( ranges::equal(*i++, "the"sv) );
+  VERIFY( ranges::equal(*i++, "quick"sv) );
+  VERIFY( ranges::equal(*i++, "brown"sv) );
+  VERIFY( ranges::equal(*i++, "fox"sv) );
+  VERIFY( i == v.end() );
+}
+
+void
+test05()
+{
+  auto as_string = [](ranges::view auto rng) {
+    auto in = rng | views::common;
+    return std::string(in.begin(), in.end());
+  };
+  std::string str
+    = "Now is the time for all good men to come to the aid of their county.";
+  auto rng
+    = str | views::split(' ') | views::transform(as_string) | views::common;
+  std::vector<std::string> words(rng.begin(), rng.end());
+  auto not_space_p = [](char c) { return c != ' '; };
+  VERIFY( ranges::equal(words | views::join,
+			str | views::filter(not_space_p)) );
+}
+
+template<auto split = views::split>
+void
+test06()
+{
+  // Verify SFINAE behavior.
+  std::string s, p;
+  static_assert(!requires { split(); });
+  static_assert(!requires { split(s, p, 0); });
+  static_assert(!requires { split(p)(); });
+  static_assert(!requires { s | split; });
+
+  static_assert(!requires { s | split(p); });
+  static_assert(!requires { split(p)(s); });
+  static_assert(!requires { s | (split(p) | views::all); });
+  static_assert(!requires { (split(p) | views::all)(s); });
+
+  static_assert(requires { s | split(views::all(p)); });
+  static_assert(requires { split(views::all(p))(s); });
+  static_assert(requires { s | (split(views::all(p)) | views::all); });
+  static_assert(requires { (split(views::all(p)) | views::all)(s); });
+
+  auto adapt = split(p);
+  static_assert(requires { s | adapt; });
+  static_assert(requires { adapt(s); });
+
+  auto adapt2 = split(p) | views::all;
+  static_assert(requires { s | adapt2; });
+  static_assert(requires { adapt2(s); });
+}
+
+void
+test10()
+{
+  // LWG 3505
+  auto to_string = [] (auto r) {
+    return std::string(r.begin(), ranges::next(r.begin(), r.end()));
+  };
+  auto v = "xxyx"sv | views::split("xy"sv) | views::transform(to_string);
+  VERIFY( ranges::equal(v, (std::string_view[]){"x", "x"}) );
+}
+
+void
+test11()
+{
+  // LWG 3478
+  static_assert(ranges::distance(views::split("text"sv, "text"sv)) == 2);
+  static_assert(ranges::distance(views::split(" text "sv, ' ')) == 3);
+  static_assert(ranges::distance(views::split(" t e x t "sv, ' ')) == 6);
+  static_assert(ranges::distance(views::split("  text  "sv, "  "sv)) == 3);
+  static_assert(ranges::distance(views::split("  text    "sv, "  "sv)) == 4);
+  static_assert(ranges::distance(views::split("  text     "sv, "  "sv)) == 4);
+  static_assert(ranges::distance(views::split("t"sv, 't')) == 2);
+  static_assert(ranges::distance(views::split("text"sv, ""sv)) == 4);
+}
+} // namespace from_lazy_split_cc
+
+int
+main()
+{
+  test01();
+
+  from_lazy_split_cc::test01();
+  from_lazy_split_cc::test02();
+  from_lazy_split_cc::test03();
+  from_lazy_split_cc::test04();
+  from_lazy_split_cc::test05();
+  from_lazy_split_cc::test06();
+  from_lazy_split_cc::test10();
+  from_lazy_split_cc::test11();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/p2325.cc b/libstdc++-v3/testsuite/std/ranges/p2325.cc
index 4d075409026..d2ebe9af863 100644
--- a/libstdc++-v3/testsuite/std/ranges/p2325.cc
+++ b/libstdc++-v3/testsuite/std/ranges/p2325.cc
@@ -124,6 +124,20 @@ test08()
   static_assert(default_initializable<type4>);
 }
 
+void
+test08a()
+{
+  // Verify split_view is conditionally default constructible.
+  using type1 = ranges::split_view<ranges::ref_view<int[2]>, ranges::single_view<int>>;
+  static_assert(!default_initializable<type1>);
+  using type2 = ranges::split_view<ranges::single_view<int>, ranges::ref_view<int[2]>>;
+  static_assert(!default_initializable<type2>);
+  using type3 = ranges::split_view<ranges::ref_view<int[2]>, ranges::ref_view<int[2]>>;
+  static_assert(!default_initializable<type3>);
+  using type4 = ranges::split_view<ranges::single_view<int>, ranges::single_view<int>>;
+  static_assert(default_initializable<type4>);
+}
+
 void
 test09()
 {
diff --git a/libstdc++-v3/testsuite/std/ranges/p2367.cc b/libstdc++-v3/testsuite/std/ranges/p2367.cc
index 5228b021602..70a0304593f 100644
--- a/libstdc++-v3/testsuite/std/ranges/p2367.cc
+++ b/libstdc++-v3/testsuite/std/ranges/p2367.cc
@@ -45,4 +45,5 @@ test01()
 
   // Verify changes to views::lazy_split.
   auto v6 = views::lazy_split(x, 5u);
+  auto v7 = views::split(x, 5u);
 }
-- 
2.32.0.93.g670b81a890