[gcc r16-3604] libstdc++: Make join_view::_Iterator::_M_get_inner noexcept [PR121804]

[Patrick Palka]

https://gcc.gnu.org/g:8e971d665a9922a73de3a37ec8e04aea975e0993

commit r16-3604-g8e971d665a9922a73de3a37ec8e04aea975e0993
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Sep 5 13:14:16 2025 -0400

    libstdc++: Make join_view::_Iterator::_M_get_inner noexcept [PR121804]
    
    Since this helper (added in r16-3576-g7f7f1878eedd80) is used in the
    noexcept-spec of iter_move and iter_swap, it in turn needs an accurate
    noexcept-spec.
    
            PR libstdc++/121804
    
    libstdc++-v3/ChangeLog:
    
            * include/std/ranges (join_view::_Iterator::_M_get_inner):
            Mark noexcept.
            * testsuite/std/ranges/adaptors/join.cc (test16): New test.
    
    Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

Diff:
---
 libstdc++-v3/include/std/ranges                    |  4 ++--
 libstdc++-v3/testsuite/std/ranges/adaptors/join.cc | 12 ++++++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index bae50d06ca81..f493da56203b 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -2935,7 +2935,7 @@ namespace views::__adaptor
 	  }
 
 	  constexpr _Inner_iter&
-	  _M_get_inner()
+	  _M_get_inner() noexcept
 	  {
 	    if constexpr (forward_iterator<_Inner_iter>)
 	      return _M_inner;
@@ -2944,7 +2944,7 @@ namespace views::__adaptor
 	  }
 
 	  constexpr const _Inner_iter&
-	  _M_get_inner() const
+	  _M_get_inner() const noexcept
 	  {
 	    if constexpr (forward_iterator<_Inner_iter>)
 	      return _M_inner;
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/join.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/join.cc
index a9395b489919..db7749045c23 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/join.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/join.cc
@@ -240,6 +240,17 @@ test15()
   constexpr decltype(views::join(views::single(views::single(0))).begin()) it;
 }
 
+void
+test16()
+{
+  // PR libstdc++/121804 - join_view::iterator::_M_get_inner should be noexcept
+  std::vector<std::vector<int>> vv;
+  ranges::join_view j{vv};
+  auto jit = j.begin();
+  static_assert(noexcept(ranges::iter_move(jit)));
+  static_assert(noexcept(ranges::iter_swap(jit, jit)));
+}
+
 int
 main()
 {
@@ -258,4 +269,5 @@ main()
   test13();
   test14();
   test15();
+  test16();
 }