libstdc++: Implement P2210 changes to split_view resolving LWG 3478

This implements the part of P2210R2 "Superior String Splitting" that
resolves LWG 3478.

libstdc++-v3/ChangeLog:

	* include/std/ranges (split_view::_OuterIter::__at_end):
	Check _M_trailing_empty.
	(split_view::_OuterIter::_M_trailing_empty): Define this
	data member.
	(split_view::_OuterIter::operator++): Set _M_trailing_empty
	appropriately.
	(split_view::_OuterIter::operator==): Compare
	_M_trailing_empty.
	* testsuite/std/ranges/adaptors/100479.cc (test03): Expect two
	split parts instead of one.
	* testsuite/std/ranges/adaptors/split.cc (test11): New test.

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 7cb8b2d..5eba691 100644 (file)
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -2879,7 +2879,7 @@ namespace views::__adaptor
 
          constexpr bool
          __at_end() const
-         { return __current() == ranges::end(_M_parent->_M_base); }
+         { return __current() == ranges::end(_M_parent->_M_base) && !_M_trailing_empty; }
 
          // [range.split.outer] p1
          //  Many of the following specifications refer to the notional member
@@ -2909,6 +2909,7 @@ namespace views::__adaptor
          [[no_unique_address]]
            __detail::__maybe_present_t<forward_range<_Vp>,
                                        iterator_t<_Base>> _M_current;
+         bool _M_trailing_empty = false;
 
        public:
          using iterator_concept = conditional_t<forward_range<_Base>,
@@ -2971,7 +2972,10 @@ namespace views::__adaptor
            // 3505. split_view::outer-iterator::operator++ misspecified
            const auto __end = ranges::end(_M_parent->_M_base);
            if (__current() == __end)
-             return *this;
+             {
+               _M_trailing_empty = false;
+               return *this;
+             }
            const auto [__pbegin, __pend] = subrange{_M_parent->_M_pattern};
            if (__pbegin == __pend)
              ++__current();
@@ -2980,7 +2984,11 @@ namespace views::__adaptor
                __current() = ranges::find(std::move(__current()), __end,
                                           *__pbegin);
                if (__current() != __end)
-                 ++__current();
+                 {
+                   ++__current();
+                   if (__current() == __end)
+                     _M_trailing_empty = true;
+                 }
              }
            else
              do
@@ -2990,6 +2998,8 @@ namespace views::__adaptor
                  if (__p == __pend)
                    {
                      __current() = __b;
+                     if (__current() == __end)
+                       _M_trailing_empty = true;
                      break;
                    }
                } while (++__current() != __end);
@@ -3012,7 +3022,10 @@ namespace views::__adaptor
          friend constexpr bool
          operator==(const _OuterIter& __x, const _OuterIter& __y)
            requires forward_range<_Base>
-         { return __x._M_current == __y._M_current; }
+         {
+           return __x._M_current == __y._M_current
+             && __x._M_trailing_empty == __y._M_trailing_empty;
+         }
 
          friend constexpr bool
          operator==(const _OuterIter& __x, default_sentinel_t)

diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/100479.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/100479.cc
index ba10b7b..b166790 100644 (file)
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/100479.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/100479.cc
@@ -95,11 +95,11 @@ test03()
     | views::drop_while([](auto) { return false; })
     | views::filter([](auto) { return true; });
   static_assert(ranges::forward_range<decltype(v)>);
-  VERIFY( ranges::next(v.begin()) == v.end() );
+  VERIFY( ranges::distance(v) == 2 );
   auto w = v;
-  VERIFY( ranges::next(w.begin()) == w.end() );
+  VERIFY( ranges::distance(v) == 2 );
   auto z = std::move(w);
-  VERIFY( ranges::next(z.begin()) == z.end() );
+  VERIFY( ranges::distance(v) == 2 );
   return true;
 }
 

diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/split.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/split.cc
index 9d2cfa8..2158568 100644 (file)
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/split.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/split.cc
@@ -193,6 +193,25 @@ test10()
   VERIFY( ranges::equal(v, (std::string_view[]){"x", "x"}) );
 }
 
+void
+test11()
+{
+  // LWG 3478
+  auto v = views::split("text"sv, "text"sv);
+  auto i = v.begin();
+  VERIFY( ranges::empty(*i++) );
+  VERIFY( ranges::empty(*i++) );
+  VERIFY( i == v.end() );
+
+  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);
+}
+
 int
 main()
 {
@@ -206,4 +225,5 @@ main()
   test08();
   test09();
   test10();
+  test11();
 }