[libc++] LWG4012: common_view::begin/end are missing the simple-view check (#153674)

close #105320

libcxx/docs/Status/Cxx2cIssues.csv

@@ -46,7 +46,7 @@
 "`LWG3975 <https://wg21.link/LWG3975>`__","Specializations of ``basic_format_context`` should not be permitted","2024-03 (Tokyo)","|Nothing To Do|","","`#105317 <https://github.com/llvm/llvm-project/issues/105317>`__",""
 "`LWG3984 <https://wg21.link/LWG3984>`__","``ranges::to``'s recursion branch may be ill-formed","2024-03 (Tokyo)","|Complete|","19","`#105318 <https://github.com/llvm/llvm-project/issues/105318>`__",""
 "`LWG4011 <https://wg21.link/LWG4011>`__","""`Effects`: Equivalent to return"" in ``[span.elem]``","2024-03 (Tokyo)","|Nothing To Do|","","`#105319 <https://github.com/llvm/llvm-project/issues/105319>`__",""
-"`LWG4012 <https://wg21.link/LWG4012>`__","``common_view::begin/end`` are missing the ``simple-view`` check","2024-03 (Tokyo)","","","`#105320 <https://github.com/llvm/llvm-project/issues/105320>`__",""
+"`LWG4012 <https://wg21.link/LWG4012>`__","``common_view::begin/end`` are missing the ``simple-view`` check","2024-03 (Tokyo)","|Complete|","23","`#105320 <https://github.com/llvm/llvm-project/issues/105320>`__",""
 "`LWG4013 <https://wg21.link/LWG4013>`__","``lazy_split_view::outer-iterator::value_type`` should not provide default constructor","2024-03 (Tokyo)","","","`#105321 <https://github.com/llvm/llvm-project/issues/105321>`__",""
 "`LWG4016 <https://wg21.link/LWG4016>`__","container-insertable checks do not match what container-inserter does","2024-03 (Tokyo)","|Complete|","20","`#105322 <https://github.com/llvm/llvm-project/issues/105322>`__",""
 "`LWG4023 <https://wg21.link/LWG4023>`__","Preconditions of ``std::basic_streambuf::setg/setp``","2024-03 (Tokyo)","|Complete|","19","`#105323 <https://github.com/llvm/llvm-project/issues/105323>`__",""

libcxx/test/std/ranges/range.adaptors/range.common.view/begin.pass.cpp

@@ -51,6 +51,12 @@ constexpr bool test() {
     assert(begin == std::ranges::begin(view));
   }
 
+  {
+    NonSimpleNonCommonView view{buf, buf + 8};
+    std::ranges::common_view<NonSimpleNonCommonView> common(view);
+    static_assert(!std::is_same_v<decltype(common.begin()), decltype(std::as_const(common).begin())>);
+  }
+
   return true;
 }
 

libcxx/test/std/ranges/range.adaptors/range.common.view/end.pass.cpp

@@ -39,6 +39,12 @@ constexpr bool test() {
     assert(base(end) == buf + 8);
   }
 
+  {
+    NonSimpleNonCommonView view{buf, buf + 8};
+    std::ranges::common_view<NonSimpleNonCommonView> common(view);
+    static_assert(!std::is_same_v<decltype(common.end()), decltype(std::as_const(common).end())>);
+  }
+
   return true;
 }
 

libcxx/test/std/ranges/range.adaptors/range.common.view/types.h

@@ -90,4 +90,37 @@ struct NonCommonView : std::ranges::view_base {
 static_assert( std::ranges::view<NonCommonView>);
 static_assert(!std::ranges::common_range<NonCommonView>);
 
+template <class T>
+concept HasConstBegin = requires(const T& ct) { ct.begin(); };
+
+template <class T>
+concept HasBegin = requires(T& t) { t.begin(); };
+
+template <class T>
+concept HasConstAndNonConstBegin = HasConstBegin<T> && requires(T& t, const T& ct) {
+  requires !std::same_as<decltype(t.begin()), decltype(ct.begin())>;
+};
+
+template <class T>
+concept HasOnlyNonConstBegin = HasBegin<T> && !HasConstBegin<T>;
+
+template <class T>
+concept HasOnlyConstBegin = HasConstBegin<T> && !HasConstAndNonConstBegin<T>;
+
+struct NonSimpleNonCommonView : std::ranges::view_base {
+  int* begin_;
+  int* end_;
+  constexpr explicit NonSimpleNonCommonView(int* b, int* e) : begin_(b), end_(e) {}
+  constexpr auto begin() const { return static_cast<const int*>(begin_); }
+  constexpr auto end() const { return sentinel_wrapper<const int*>(end_); }
+  constexpr int* begin() { return begin_; }
+  constexpr auto end() { return sentinel_wrapper<int*>(end_); }
+};
+
+static_assert(!HasOnlyNonConstBegin<std::ranges::common_view<NonSimpleNonCommonView>>);
+static_assert(!HasOnlyConstBegin<std::ranges::common_view<NonSimpleNonCommonView>>);
+static_assert(HasConstAndNonConstBegin<std::ranges::common_view<NonSimpleNonCommonView>>);
+static_assert(HasConstBegin<const std::ranges::common_view<NonSimpleNonCommonView>>);
+static_assert(HasOnlyConstBegin<const std::ranges::common_view<NonSimpleNonCommonView>>);
+
 #endif // TEST_STD_RANGES_RANGE_ADAPTORS_RANGE_COMMON_VIEW_TYPES_H