libstdc++: Add missing initializers for __maybe_present_t members [PR119962]

Data members of type __maybe_present_t where the conditionally present
type might be an aggregate or fundamental type need to be explicitly
value-initialized (rather than implicitly default-initialized), so that
default-initialization of the containing class always results in an
completely initialized object.

	PR libstdc++/119962

libstdc++-v3/ChangeLog:

	* include/std/ranges (join_view::_Iterator::_M_outer): Initialize.
	(lazy_split_view::_OuterIter::_M_current): Initialize.
	(join_with_view::_Iterator::_M_outer_it): Initialize.
	* testsuite/std/ranges/adaptors/join.cc (test15): New test.
	* testsuite/std/ranges/adaptors/join_with/1.cc (test05): New test.
	* testsuite/std/ranges/adaptors/lazy_split.cc (test13): New test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

4 files changed, 30 insertions, 3 deletions

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 3a6710b..efe6296 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -3022,7 +3022,8 @@ namespace views::__adaptor
 	  { _M_satisfy(); }
 
 	  [[no_unique_address]]
-	    __detail::__maybe_present_t<forward_range<_Base>, _Outer_iter> _M_outer;
+	    __detail::__maybe_present_t<forward_range<_Base>, _Outer_iter> _M_outer
+	      = decltype(_M_outer)();
 	  optional<_Inner_iter> _M_inner;
 	  _Parent* _M_parent = nullptr;
 
@@ -3376,7 +3377,8 @@ namespace views::__adaptor
 
 	  [[no_unique_address]]
 	    __detail::__maybe_present_t<forward_range<_Vp>,
-					iterator_t<_Base>> _M_current;
+					iterator_t<_Base>> _M_current
+	      = decltype(_M_current)();
 	  bool _M_trailing_empty = false;
 
 	public:
@@ -7400,7 +7402,8 @@ namespace views::__adaptor
 
     _Parent* _M_parent = nullptr;
     [[no_unique_address]]
-      __detail::__maybe_present_t<forward_range<_Base>, _OuterIter> _M_outer_it;
+      __detail::__maybe_present_t<forward_range<_Base>, _OuterIter> _M_outer_it
+	= decltype(_M_outer_it)();
     variant<_PatternIter, _InnerIter> _M_inner_it;
 
     constexpr _OuterIter&
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/join.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/join.cc
index 2861115..a9395b4 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/join.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/join.cc
@@ -233,6 +233,13 @@ test14()
   VERIFY( ranges::equal(v | views::join, (int[]){1, 2, 3}) );
 }
 
+void
+test15()
+{
+  // PR libstdc++/119962 - __maybe_present_t misses initialization
+  constexpr decltype(views::join(views::single(views::single(0))).begin()) it;
+}
+
 int
 main()
 {
@@ -250,4 +257,5 @@ main()
   test12();
   test13();
   test14();
+  test15();
 }
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/join_with/1.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/join_with/1.cc
index 8ab30a5..4d55c9d 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/join_with/1.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/join_with/1.cc
@@ -94,6 +94,13 @@ test04()
   return true;
 }
 
+void
+test05()
+{
+  // PR libstdc++/119962 - __maybe_present_t misses initialization
+  constexpr decltype(views::join_with(views::single(views::single(0)), 0).begin()) it;
+}
+
 int
 main()
 {
@@ -105,4 +112,5 @@ main()
 #else
   VERIFY(test04());
 #endif
+  test05();
 }
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/lazy_split.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/lazy_split.cc
index 81fc60b..321ae27 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/lazy_split.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/lazy_split.cc
@@ -232,6 +232,13 @@ test12()
   return true;
 }
 
+void
+test13()
+{
+  // PR libstdc++/119962 - __maybe_present_t misses initialization
+  constexpr decltype(views::lazy_split(views::single(0), 0).begin()) it;
+}
+
 int
 main()
 {
@@ -247,4 +254,5 @@ main()
   test10();
   test11();
   static_assert(test12());
+  test13();
 }