[libcxx-commits] [PATCH] D115686: [libc++] [ranges] Introduce _LIBCPP_AUTO_CAST(x) for auto(x)

[Arthur O'Dwyer via Phabricator via libcxx-commits]

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Clang is gaining `auto(x)` support in D113393 <https://reviews.llvm.org/D113393>, but sadly there seems to be no feature-test macro for it.

Use this where C++20 specifies we should use `auto(x)`; stop using `__decay_copy(x)`, which calls more move-constructors than it should.
Add regression tests.

Drive-by fix some places in `std::ranges::size` that were perfect-forwarding when they shouldn't; this affects one test case. Did this only because I was touching those lines already: `__decay_copy(forward(x))` becomes just `_LIBCPP_AUTO_CAST(x)`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D115686

Files:
  libcxx/include/CMakeLists.txt
  libcxx/include/__ranges/access.h
  libcxx/include/__ranges/size.h
  libcxx/include/__utility/auto_cast.h
  libcxx/include/module.modulemap
  libcxx/include/utility
  libcxx/test/std/ranges/range.access/range.access.begin/begin.pass.cpp
  libcxx/test/std/ranges/range.access/range.access.end/end.pass.cpp
  libcxx/test/std/ranges/range.access/range.prim/size.pass.cpp

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