Mordante added a subscriber: var-const.
Mordante added a comment.
In D152003#4534963 <https://reviews.llvm.org/D152003#4534963>, @Fznamznon wrote:
>> What do you mean with libstdc++ is fine?
>
> What I mean is when I do (current patch is applied to clang):
>
> source/llvm-project/build/bin/clang++ -std=c++20 t.cpp -c // compilation
> succeeds
I see what you mean now.
> What I'm seeing is that in libc++ there is a bunch of explicit static casts
> in `ranges::__crend::__fn` that endup transformed:
>
> namespace ranges {
> namespace __crend {
>
> struct __fn {
> template <class _Tp>
> requires is_lvalue_reference_v<_Tp&&>
>
> [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
> constexpr auto operator()(_Tp&& __t) const
> noexcept(noexcept(ranges::rend(static_cast<const
> remove_reference_t<_Tp>&>(__t))))
> -> decltype( ranges::rend(static_cast<const
> remove_reference_t<_Tp>&>(__t)))
> { return ranges::rend(static_cast<const
> remove_reference_t<_Tp>&>(__t)); }
>
>
> template <class _Tp>
>
> requires is_rvalue_reference_v<_Tp&&>
>
> [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
> constexpr auto operator()(_Tp&& __t) const
> noexcept(noexcept(ranges::rend(static_cast<const _Tp&&>(__t))))
>
> -> decltype( ranges::rend(static_cast<const _Tp&&>(__t)))
> { return ranges::rend(static_cast<const _Tp&&>(__t)); }
> };
> } // namespace __crend
>
> Is that expected?
I'm not very familiar with ranges but looking at the standard the `static_cast`
is not required. I don't think the original author intended this behaviour
which you implement in this patch. (To be honest I'm a bit surprised by this
change in the language. I wonder how many other (library) developers it will
catch off-guard.)
I agree this is a bug in libc++ and we should fix it. As mentioned I'm not too
familiar with ranges. Maybe @var-const has time, otherwise
we need to wait for @philnik.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D152003/new/
https://reviews.llvm.org/D152003
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