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The changes in r12-4381 were intended to reduce memory usage, but replacing the __contiguous constant in __string_from_range with the new __is_contiguous variable template caused a regression. The old code checked is_pointer_v<decltype(std::__niter_base(__first))> but he new code just checks is_pointer_v<_InputIterator>. This means that we no longer recognise basic_string::iterator and vector::iterator as contiguous, and so return a temporary basic_string instead of a basic_string_view. This only affects C++17 mode, because the std::contiguous_iterator concept is used in C++20 which gives the right answer for __normal_iterator (and more types as well). The fix is to specialize the new __is_contiguous variable template so it is true for __normal_iterator<T*, C> specializations. The new partial specializations are defined for C++20 too, because it should be cheaper to match the partial specialization than to check whether the std::contiguous_iterator concept is satisfied. libstdc++-v3/ChangeLog: * include/bits/fs_path.h (__detail::__is_contiguous): Add partial specializations for pointers and __normal_iterator.
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