libstdc++: [_GLIBCXX_DEBUG] Fix assignment of value-initialized iterator [PR112477]

Now that _M_Detach do not reset iterator _M_version value we need to reset it when
the iterator is attached to a new sequence, even if this sequencer is null when
assigning a value-initialized iterator. In this case _M_version shall be resetted to 0.

libstdc++-v3/ChangeLog:

	PR libstdc++/112477
	* src/c++11/debug.cc
	(_Safe_iterator_base::_M_attach): Reset _M_version to 0 if attaching to null
	sequence.
	(_Safe_iterator_base::_M_attach_single): Likewise.
	(_Safe_local_iterator_base::_M_attach): Likewise.
	(_Safe_local_iterator_base::_M_attach_single): Likewise.
	* testsuite/23_containers/map/debug/112477.cc: New test case.

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

1 files changed, 20 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/23_containers/map/debug/112477.cc b/libstdc++-v3/testsuite/23_containers/map/debug/112477.cc
new file mode 100644
index 0000000..bde613b
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/map/debug/112477.cc
@@ -0,0 +1,20 @@
+// { dg-do run { target c++11 } }
+// { dg-require-debug-mode "" }
+
+// PR libstdc++/112477
+
+#include <map>
+
+int main()
+{
+  using M = std::map<int, int>;
+  using I = M::iterator;
+
+  M map{ {1, 1}, {2, 2} };
+
+  I it1 = map.begin();
+  it1 = I{};
+
+  I it2{};
+  (void)(it1 == it2);
+}