[all-commits] [llvm/llvm-project] 40a6be: [libc++] Ensure valid view for view_interface temp...

[Joseph Loser via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 40a6be4346097c008998d702381b07acbc6c9ae2
      https://github.com/llvm/llvm-project/commit/40a6be4346097c008998d702381b07acbc6c9ae2
  Author: Joe Loser <joeloser93 at gmail.com>
  Date:   2021-10-29 (Fri, 29 Oct 2021)

  Changed paths:
    M libcxx/include/__ranges/view_interface.h

  Log Message:
  -----------
  [libc++] Ensure valid view for view_interface template parameter

Some types that inherit from `view_interface` do not meet the
preconditions. This came up during discussion
in https://reviews.llvm.org/D112631. Currently, the behavior is IFNDR,
but the preconditions can be easily checked, so let's do so.

In particular, we know each public member function calls the
`__derived()` private function, so we can do the check there. We
intentionally do it as a `static_assert` instead of a `requires` clause
to avoid hard erroring in some cases, such as with incomplete types. An
example hard error is:

```
llvm-project/build/include/c++/v1/__ranges/view_interface.h:48:14: note: because 'sizeof(_Tp)' would be invalid: invalid application of 'sizeof' to an incomplete type 'MoveOnlyForwardRange'
  requires { sizeof(_Tp); } &&
             ^
llvm-project/build/include/c++/v1/__ranges/view_interface.h:73:26: error: no matching member function for call to '__derived'
    return ranges::begin(__derived()) == ranges::end(__derived());
                         ^~~~~~~~~
llvm-project/libcxx/test/std/ranges/range.utility/view.interface/view.interface.pass.cpp:187:31: note: in instantiation of function template specialization 'std::ranges::view_interface<MoveOnlyForwardRange>::empty<Mov
eOnlyForwardRange>' requested here
  assert(!std::move(moveOnly).empty());
```

Reviewed By: Quuxplusone, Mordante, #libc

Differential Revision: https://reviews.llvm.org/D112665