[libc++] Refactor the test for join_view's default constructor

[ldionne]

Summary

In particular, this removes the need for adding a ad-hoc operator==
to forward_iterator.

[• Quuxplusone]

Wow, that old code was crazy complicated for the fact that this is all it's doing. Nice cleanup.

libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/ctor.default.pass.cpp

30

Rename to JoinView? (I don't understand whatever distinction you're making between JoinX and JoinedX.)
Throughout, I'd rename Iter -> It, and in fact I'd get rid of the custom view helper class in favor of std::subrange:

template <class It>
constexpr void test_default_constructible() {
  using View = std::subrange<It, sentinel_wrapper<It>>;
  using JoinIterator = std::ranges::iterator_t<std::ranges::join_view<View>>;
  static_assert(std::is_default_constructible_v<JoinIterator>);
  JoinIterator it; (void)it;
}

Likewise below.

[ldionne]

Apply review comments.

libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/ctor.default.pass.cpp

30

There's no distinction between JoinedView and JoinView, just my own inconsistency. Thanks for spotting. I'm also fine with renaming Iter to It, but I'll keep view instead of std::subrange in order to keep the test as minimal as possible.

libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/ctor.default.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: libcpp-no-concepts
 // UNSUPPORTED: libcpp-has-no-incomplete-ranges
 
 // iterator() requires default_initializable<OuterIter> = default;
 
-#include <cassert>
 #include <ranges>
 
-#include "test_macros.h"
+#include <cassert>
+#include <type_traits>
+#include "test_iterators.h"
 #include "../types.h"
 
-template<class T>
-struct DefaultCtorParent : std::ranges::view_base {
-  T *ptr_;
-  constexpr DefaultCtorParent(T *ptr) : ptr_(ptr) {}
-
-  constexpr forward_iterator<T *> begin() { return forward_iterator<T *>(ptr_); }
-  constexpr forward_iterator<const T *> begin() const { return forward_iterator<const T *>(ptr_); }
-  constexpr T *end() { return ptr_ + 4; }
-  constexpr const T *end() const { return ptr_ + 4; }
+template <class Iter>
+struct view : std::ranges::view_base {
+  Iter begin() const;
+  sentinel_wrapper<Iter> end() const;
 };
 
-template<class T>
-constexpr bool operator==(const forward_iterator<T*> &lhs, const T *rhs) { return lhs.base() == rhs; }
-template<class T>
-constexpr bool operator==(const T *lhs, const forward_iterator<T*> &rhs) { return rhs.base() == lhs; }
-
-constexpr bool test() {
-  using Base = DefaultCtorParent<ChildView>;
-  // Note, only the outer iterator is default_initializable:
-  static_assert( std::default_initializable<std::ranges::iterator_t<Base>>);
-  static_assert(!std::default_initializable<std::ranges::iterator_t<std::ranges::range_reference_t<Base>>>);
-
-  std::ranges::iterator_t<std::ranges::join_view<Base>> iter1;
-  (void) iter1;
+template <class Iter>
+constexpr void test_default_constructible() {
+  using JoinedView = std::ranges::join_view<view<Iter>>;
+  using JoinIterator = std::ranges::iterator_t<JoinedView>;
+  static_assert(std::is_default_constructible_v<JoinIterator>);
+  JoinIterator it; (void)it;
+}
 
-  static_assert(!std::default_initializable<std::ranges::iterator_t<std::ranges::join_view<ParentView<ChildView>>>>);
+template <class Iter>
+constexpr void test_non_default_constructible() {
+  using JoinedView = std::ranges::join_view<view<Iter>>;
+  using JoinIterator = std::ranges::iterator_t<JoinedView>;
+  static_assert(!std::is_default_constructible_v<JoinIterator>);
+}
 
+constexpr bool test() {
+  test_non_default_constructible<cpp17_input_iterator<ChildView*>>();
+  // NOTE: cpp20_input_iterator can't be used with join_view because it is not copyable.
+  test_default_constructible<forward_iterator<ChildView*>>();
+  test_default_constructible<bidirectional_iterator<ChildView*>>();
+  test_default_constructible<random_access_iterator<ChildView*>>();
+  test_default_constructible<contiguous_iterator<ChildView*>>();
   return true;
 }
 
 int main(int, char**) {
   test();
   static_assert(test());
-
   return 0;
 }