* Update to Clang 10 and Visual Studio 2019 version 16.6p2
* re-clang-formats the tree to comply with new clang 10 clang-format
* updates our agents to F series VMs which are faster and cheaper for our build workloads
* defaults scale set to 0 VMs and lets the Azure Pipelines service control all resizing
* fix tests to pass with the new compilers
Co-authored by Casey Carter and Curtis Bezault
`iter_value_t` doesn't detour through `iterator_traits`, so it can be valid for non-iterator types. This breaks `_Is_Source2`, however, which expects `_Iter_value_t` to filter out non-iterator types.
Drive-by: rename `_Is_Source2` to `_Is_Source_impl` to be consistent with how we name trait helpers elsewhere.
Fixes DevCom-953628.
Resolves GH-615 / DevCom-950424.
* Extract _Is_file_not_found to <xfilesystem_abi.h> as __std_is_file_not_found because we also need that in filesystem.cpp.
* Add ERROR_BAD_NETPATH to __std_is_file_not_found.
* Map ERROR_BAD_NETPATH to errc::no_such_file_or_directory.
* Change filesystem tests that look for file not exists behavior to also test bad network paths.
Implements iterator primitive operations `std::ranges::advance`, `std::ranges::next`, `std::ranges::prev`, and `std::ranges::distance`; as well as `std::default_sentinel` and `std::unreachable_sentinel`.
This change reworks the STL's iterator unwrapping machinery to enable unwrapping of C++20 move-only single-pass iterators (and `if constepxr`s all the things). Consequently, `_Iter_ref_t`, `_Iter_value_t`, and `_Iter_diff_t` resolve to `iter_reference_t`, `iter_value_t`, and `iter_difference_t` (respectively) in `__cpp_lib_concepts` (soon to be C++20) mode. This change necessitates some fixes to `unique_copy` and `_Fill_memset_is_safe` which both assume that `_Iter_value_t<T>` is well-formed for any iterator `T`. (`iter_value_t<T>` does not have that property: it is only well-formed when `readable<T>`.)
I notably haven't unified `default_sentinel_t` with `_Default_sentinel` out of an abundance of paranoia. Our `move_iterator` is comparable with `_Default_sentinel`, which is not the case for `std::default_sentinel`.
Drive-by:
* This change `if constexpr`-izes `unique_copy`.
Stephan T. Lavavej
Billy O'Neal
Casey Carter
Jean Philippe
Julie Philip James
Daniel Marshall