[PATCH] D152003: [clang] Fix `static_cast` to array of unknown bound

[Mark de Wever via Phabricator via cfe-commits]

Mordante added a comment.

In D152003#4531404 <https://reviews.llvm.org/D152003#4531404>, @Fznamznon wrote:

>> should we try to land that today?
>
> I'm not sure. It causes failures in libc++ testing:
>
>   Failed Tests (3):
>     llvm-libc++-shared.cfg.in :: std/ranges/range.access/end.pass.cpp
>     llvm-libc++-shared.cfg.in :: std/ranges/range.access/rbegin.pass.cpp
>     llvm-libc++-shared.cfg.in :: std/ranges/range.access/rend.pass.cpp
>
> I haven't figured out why. Trying to compile:
>
>   #include <ranges>
>   
>   using RangeCREndT = decltype(std::ranges::crend);
>   static_assert(!std::is_invocable_v<RangeCREndT, int (&)[]>);
>
> fails with this patch only using libc++, libstdc++ is fine. I'm not sure it is my misunderstanding, bug in the patch or bug in libc++.

What do you mean with libstdc++ is fine?
The reduced tests passed with libcstd++ https://godbolt.org/z/nh9v8cedr
The change seems to break libc++.

Based on the bug and this patch I am correct that "transformation" of an array of unknown bounds to anarray of known bounds only happens with an explicit cast and not implicitly?

I have a strong suspicion that this patch changes the test to

  #include <ranges>
  
  using RangeCREndT = decltype(std::ranges::crend);
  static_assert(!std::is_invocable_v<RangeCREndT, int (&)[1]>); // no longer an array of unknown bound so the assert fails

Can you look at the AST output of the failed example to verify my hypothesis? When you think libc++ is wrong can you then post this AST?


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https://reviews.llvm.org/D152003