libstdc++: extraneous begin in cartesian_product_view::end [PR107572]

ranges::begin() isn't guaranteed to be equality-preserving for non-forward
ranges, so in cartesian_product_view::end we need to avoid needlessly
calling begin() on the first range (which could be non-forward) in the
case where __empty_tail is false as per its specification.

Since we're already using a variadic lambda to compute __empty_tail, we
might as well use that same lambda to build up the tuple of iterators
instead of building it separately via e.g. std::apply or __tuple_transform.

	PR libstdc++/107572

libstdc++-v3/ChangeLog:

	* include/std/ranges (cartesian_product_view::end): When
	building the tuple of iterators, avoid calling ranges::begin on
	the first range if __empty_tail is false.
	* testsuite/std/ranges/cartesian_product/1.cc (test07): New test.

0 files changed, 0 insertions, 0 deletions