libstdc++: Add comparisons to std::default_sentinel_t (LWG 3719)

This library defect was recently approved for C++23.

libstdc++-v3/ChangeLog:

	* include/bits/fs_dir.h (directory_iterator): Add comparison
	with std::default_sentinel_t. Remove redundant operator!= for
	C++20.
	* (recursive_directory_iterator): Likewise.
	* include/bits/iterator_concepts.h [!__cpp_lib_concepts]
	(default_sentinel_t, default_sentinel): Define even if concepts
	are not supported.
	* include/bits/regex.h (regex_iterator): Add comparison with
	std::default_sentinel_t. Remove redundant operator!= for C++20.
	(regex_token_iterator): Likewise.
	(regex_token_iterator::_M_end_of_seq()): Add noexcept.
	* testsuite/27_io/filesystem/iterators/lwg3719.cc: New test.
	* testsuite/28_regex/iterators/regex_iterator/lwg3719.cc:
	New test.
	* testsuite/28_regex/iterators/regex_token_iterator/lwg3719.cc:
	New test.

3 files changed, 97 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/27_io/filesystem/iterators/lwg3719.cc b/libstdc++-v3/testsuite/27_io/filesystem/iterators/lwg3719.cc
new file mode 100644
index 00000000000..c19cddc74f9
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/filesystem/iterators/lwg3719.cc
@@ -0,0 +1,39 @@
+// { dg-options "-std=gnu++20" }
+// { dg-do run { target c++20 } }
+// { dg-require-filesystem-ts "" }
+
+#include <filesystem>
+#include <iterator>
+#include <testsuite_hooks.h>
+
+// LWG 3719. Directory iterators should be usable with default sentinel
+
+void
+test_dir_iter()
+{
+  std::filesystem::directory_iterator d0;
+  VERIFY( d0 == std::default_sentinel );
+  std::filesystem::directory_iterator d1(".");
+  VERIFY( d1 != std::default_sentinel );
+
+  static_assert( noexcept(d0 == std::default_sentinel) );
+  static_assert( noexcept(d0 != std::default_sentinel) );
+}
+
+void
+test_recursive_dir_iter()
+{
+  std::filesystem::recursive_directory_iterator d0;
+  VERIFY( d0 == std::default_sentinel );
+  std::filesystem::recursive_directory_iterator d1(".");
+  VERIFY( d1 != std::default_sentinel );
+
+  static_assert( noexcept(d0 == std::default_sentinel) );
+  static_assert( noexcept(d0 != std::default_sentinel) );
+}
+
+int main()
+{
+  test_dir_iter();
+  test_recursive_dir_iter();
+}
diff --git a/libstdc++-v3/testsuite/28_regex/iterators/regex_iterator/lwg3719.cc b/libstdc++-v3/testsuite/28_regex/iterators/regex_iterator/lwg3719.cc
new file mode 100644
index 00000000000..e8c8f79364a
--- /dev/null
+++ b/libstdc++-v3/testsuite/28_regex/iterators/regex_iterator/lwg3719.cc
@@ -0,0 +1,29 @@
+// { dg-options "-std=gnu++20" }
+// { dg-do run { target c++20 } }
+
+#include <regex>
+#include <iterator>
+#include <testsuite_hooks.h>
+
+// LWG 3719. Directory iterators should be usable with default sentinel
+
+void
+test_iter()
+{
+  std::sregex_token_iterator r0;
+  VERIFY( r0 == std::default_sentinel );
+  std::string haystack = "a needle in a haystack";
+  std::regex needle("needle");
+  std::sregex_iterator r1(haystack.begin(), haystack.end(), needle);
+  VERIFY( r1 != std::default_sentinel );
+  ++r1;
+  VERIFY( r1 == std::default_sentinel );
+
+  static_assert( noexcept(r0 == std::default_sentinel) ); // GCC extension
+  static_assert( noexcept(r0 != std::default_sentinel) ); // GCC extension
+}
+
+int main()
+{
+  test_iter();
+}
diff --git a/libstdc++-v3/testsuite/28_regex/iterators/regex_token_iterator/lwg3719.cc b/libstdc++-v3/testsuite/28_regex/iterators/regex_token_iterator/lwg3719.cc
new file mode 100644
index 00000000000..5c36acead74
--- /dev/null
+++ b/libstdc++-v3/testsuite/28_regex/iterators/regex_token_iterator/lwg3719.cc
@@ -0,0 +1,29 @@
+// { dg-options "-std=gnu++20" }
+// { dg-do run { target c++20 } }
+
+#include <regex>
+#include <iterator>
+#include <testsuite_hooks.h>
+
+// LWG 3719. Directory iterators should be usable with default sentinel
+
+void
+test_iter()
+{
+  std::sregex_iterator r0;
+  VERIFY( r0 == std::default_sentinel );
+  std::string haystack = "a needle in a haystack";
+  std::regex needle("needle");
+  std::sregex_iterator r1(haystack.begin(), haystack.end(), needle);
+  VERIFY( r1 != std::default_sentinel );
+  ++r1;
+  VERIFY( r1 == std::default_sentinel );
+
+  static_assert( noexcept(r0 == std::default_sentinel) ); // GCC extension
+  static_assert( noexcept(r0 != std::default_sentinel) ); // GCC extension
+}
+
+int main()
+{
+  test_iter();
+}