libstdc++: Implement LWG 3490 change to drop_while_view::begin()

libstdc++-v3/ChangeLog:

	PR libstdc++/100606
	* include/std/ranges (drop_while_view::begin): Assert the
	precondition added by LWG 3490.

(cherry picked from commit 11784fe27d879a10dc8a79212c37f50d4f7146f3)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 3ef352949dff307d51dbe1884fdc7a488d4f294c..4e01ef57401ae32c5e0c5f1324d7238e840910b0 100644 (file)
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -2389,6 +2389,7 @@ namespace views::__adaptor
        if (_M_cached_begin._M_has_value())
          return _M_cached_begin._M_get(_M_base);
 
+       __glibcxx_assert(_M_pred.has_value());
        auto __it = __detail::find_if_not(ranges::begin(_M_base),
                                          ranges::end(_M_base),
                                          std::cref(*_M_pred));