tree 50e4625124be170d1f62860d5087a353b0ba9429
parent 10dc416c1d1b9806bdfb5053fa440a5ecd05af16
author Arthur O'Dwyer <arthur.j.odwyer@gmail.com> 1610733596 -0500
committer Copybara-Service <copybara-worker@google.com> 1612517240 -0800

[libc++] Rationalize our treatment of contiguous iterators and __unwrap_iter().

- Implement C++20's changes to `reverse_iterator`, so that it won't be
    accidentally counted as a contiguous iterator in C++20 mode.
- Implement C++20's changes to `move_iterator` as well.
- `move_iterator` should not be contiguous. This fixes a bug where
    we optimized `std::copy`-of-move-iterators in an observable way.
    Add a regression test for that bugfix.
- Add libcxx tests for `__is_cpp17_contiguous_iterator` of all relevant
    standard iterator types. Particularly check that vector::iterator
    is still considered contiguous in all C++ modes, even C++03.

After this patch, there continues to be no supported way to write your
own iterator type in C++17-and-earlier such that libc++ will consider it
"contiguous"; however, we now fully support the C++20 approach (in C++20
mode only). If you want user-defined contiguous iterators in C++17-and-earlier,
libc++'s position is "please upgrade to C++20."

Differential Revision: https://reviews.llvm.org/D94807

GitOrigin-RevId: d41c6d51cbadbbd0f81c6ac0d6628d01b881e2a5