[libcxx-commits] [PATCH] D111925: [libc++][NFC] Mark LWG3573 as complete

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

Quuxplusone requested changes to this revision.
Quuxplusone added inline comments.


================
Comment at: libcxx/test/std/strings/string.view/string.view.cons/from_iterator_sentinel.pass.cpp:54
+constexpr std::iter_difference_t<I> operator-(throwing_sized_sentinel<I>, std::input_or_output_iterator auto) {
+  throw std::runtime_error("LWG 3573");
+  return {};
----------------
Mordante wrote:
> It's possible to use Clang in a way it won't throw exceptions. This test fails in that context. Please guard all code you added with `#ifndef TEST_HAS_NO_EXCEPTIONS`. 
You should know I'm going to object every time someone adds a global-namespace overloaded operator to a type that already defines its own operators. If `throwing_sized_sentinel<I>` IS-A `sized_sentinel<I>`, then its `operator-` shouldn't be doing anything different from the existing `operator-` of `sized_sentinel<I>`.
Also, although this is a technical nitpick, I believe throwing from `operator-` in this case violates the semantic requirement in https://eel.is/c++draft/iterator.concept.sizedsentinel#2.1 , which defines what `operator-` needs to return in this case (and implicitly defines that it //does// return).
Also, `std::input_or_output_iterator auto` should be `I`, and just generally this code is way more crufty than it could be.

I think we can get by with
```
template<class CharT>
struct ThrowingSentinel {
  friend bool operator==(const CharT*, ThrowingSentinel) noexcept;
  friend int operator-(const CharT *, ThrowingSentinel) noexcept;
  friend int operator-(ThrowingSentinel, const CharT *) { throw 42; }
};

template<class CharT>
void test_throwing() {
  auto val = MAKE_STRING_VIEW(CharT, "test");
  try {
    (void)std::basic_string_view<CharT>(val.begin(), ThrowingSentinel());
    assert(false);
  } catch (int i) {
    assert(i == 42);
  }
}
~~~
  test_throwing<char>();
#ifndef TEST_HAS_NO_WIDE_CHARACTERS
  test_throwing<wchar_t>();
#endif
  test_throwing<char8_t>();
  test_throwing<char16_t>();
  test_throwing<char32_t>();
```
(I marked some undefined functions `noexcept` merely to try to be evil and trick the library into getting some intermediate noexcept-specification wrong. I don't //really// care about those noexcepts. Those functions are undefined because they will never be called.)


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D111925/new/

https://reviews.llvm.org/D111925