libstdc++: Add valid range checks to std::span constructors [PR98421]

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

libstdc++-v3/ChangeLog:

	PR libstdc++/98421
	* include/std/span (span(Iter, size_type), span(Iter, Iter)):
	Add valid range checks.
	* testsuite/23_containers/span/cons_1_assert_neg.cc: New test.
	* testsuite/23_containers/span/cons_2_assert_neg.cc: New test.

libstdc++-v3/include/std/span

@@ -160,6 +160,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    {
 	      __glibcxx_assert(__count == _Extent);
 	    }
+	  __glibcxx_requires_valid_range(__first, __first + __count);
 	}
 
       template<contiguous_iterator _It, sized_sentinel_for<_It> _End>
@@ -175,6 +176,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    {
 	      __glibcxx_assert((__last - __first) == _Extent);
 	    }
+	  __glibcxx_requires_valid_range(__first, __last);
 	}
 
       template<size_t _ArrayExtent>

libstdc++-v3/testsuite/23_containers/span/cons_1_assert_neg.cc

+// { dg-options "-std=gnu++2a" }
+// { dg-do run { xfail *-*-* } }
+// { dg-require-effective-target c++2a }
+
+#undef _GLIBCXX_DEBUG
+#define _GLIBCXX_DEBUG
+#include <span>
+#include <vector>
+
+int main()
+{
+  std::vector<int> v(2);
+  std::span<int, std::dynamic_extent> s(v.begin(), 3);
+}

libstdc++-v3/testsuite/23_containers/span/cons_2_assert_neg.cc

+// { dg-options "-std=gnu++2a" }
+// { dg-do run { xfail *-*-* } }
+// { dg-require-effective-target c++2a }
+
+#undef _GLIBCXX_DEBUG
+#define _GLIBCXX_DEBUG
+#include <span>
+#include <vector>
+
+int main()
+{
+  std::vector<int> v(2), w(1);
+  std::span<int, std::dynamic_extent> s(v.begin(), w.end());
+}