[PATCH] libstdc++: Fix up implementation of LWG 3533 [PR101589]

[Patrick Palka via Gcc-patches]

In r12-569 I accidentally applied the LWG 3533 change that
was intended for elements_view::iterator::base to
elements_view::base instead.

This patch corrects this, and also applies the corresponding LWG 3533
change to lazy_split_view::inner-iter::base now that we implement P2210.

Tested on x86_64-pc-linux-gnu, does this look OK for trunk and release
branches?

        PR libstdc++/101589

libstdc++-v3/ChangeLog:

        * include/std/ranges (lazy_split_view::_InnerIter::base): Make
        the const& overload unconstrained and return a const reference
        as per LWG 3533.  Make unconditionally noexcept.
        (elements_view::base): Revert accidental r12-569 change.
        (elements_view::_Iterator::base): Make the const& overload
        unconstrained and return a const reference as per LWG 3533.
        Make unconditionally noexcept.
---
 libstdc++-v3/include/std/ranges | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index d791e15d096..50b414e8c8c 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -3103,8 +3103,8 @@ namespace views::__adaptor
            : _M_i(std::move(__i))
          { }
 
-         constexpr iterator_t<_Base>
-         base() const& requires copyable<iterator_t<_Base>>
+         constexpr const iterator_t<_Base>&
+         base() const& noexcept
          { return _M_i_current(); }
 
          constexpr iterator_t<_Base>
@@ -3786,8 +3786,8 @@ namespace views::__adaptor
        : _M_base(std::move(base))
       { }
 
-      constexpr const _Vp&
-      base() const & noexcept
+      constexpr _Vp
+      base() const& requires copy_constructible<_Vp>
       { return _M_base; }
 
       constexpr _Vp
@@ -3913,9 +3913,8 @@ namespace views::__adaptor
            : _M_current(std::move(i._M_current))
          { }
 
-         constexpr iterator_t<_Base>
-         base() const&
-           requires copyable<iterator_t<_Base>>
+         constexpr const iterator_t<_Base>&
+         base() const& noexcept
          { return _M_current; }
 
          constexpr iterator_t<_Base>
-- 
2.32.0.349.gdaab8a564f