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

[Hristo Hristov via libcxx-commits]

================
@@ -73,21 +75,64 @@ static_assert(std::ranges::sized_range<SizedRandomAccessView>);
 struct CommonView : std::ranges::view_base {
   int* begin_;
   int* end_;
-  constexpr explicit CommonView(int* b, int* e) : begin_(b), end_(e) { }
-  constexpr int *begin() const { return begin_; }
-  constexpr int *end() const { return end_; }
+  constexpr explicit CommonView(int* b, int* e) : begin_(b), end_(e) {}
+  constexpr int* begin() const { return begin_; }
+  constexpr int* end() const { return end_; }
 };
 static_assert(std::ranges::view<CommonView>);
 static_assert(std::ranges::common_range<CommonView>);
 
 struct NonCommonView : std::ranges::view_base {
   int* begin_;
   int* end_;
-  constexpr explicit NonCommonView(int* b, int* e) : begin_(b), end_(e) { }
-  constexpr int *begin() const { return begin_; }
+  constexpr explicit NonCommonView(int* b, int* e) : begin_(b), end_(e) {}
+  constexpr int* begin() const { return begin_; }
   constexpr auto end() const { return sentinel_wrapper<int*>(end_); }
 };
-static_assert( std::ranges::view<NonCommonView>);
+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>;
+
+template <bool Simple>
+struct NonCommonBaseView : std::ranges::view_base {
+  int* begin_;
+  int* end_;
+  constexpr explicit NonCommonBaseView(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()
+    requires(!Simple)
----------------
H-G-Hristov wrote:

Is this `requires(!Simple)` necessary for this test?

https://github.com/llvm/llvm-project/pull/153674