[libc++] [chrono] Fix year_month_weekday::ok() implementation.

[mclow.lists]

The code here looks fine to me, but I want to think about the tests for a bit.
Thanks for the patch.

libcxx/include/chrono

1861

There's no need to remove this at this time.

[mclow.lists]

libcxx/test/std/utilities/time/time.cal/time.cal.ymwd/time.cal.ymwd.members/ok.pass.cpp

59–68

How about a test for the 0th Wednesday, and the -1st Tuesday?

[curdeius]

• Add tests. Update Returns commment according to [time.cal.ymwd.members]/21.

[mclow.lists]

LGTM, thanks.

libcxx/include/chrono

inline constexpr weekday  operator--(int) noexcept { weekday __tmp = *this; --(*this); return __tmp; }
          constexpr weekday& operator+=(const days& __dd) noexcept;
          constexpr weekday& operator-=(const days& __dd) noexcept;
   inline constexpr unsigned c_encoding()   const noexcept { return __wd; }
   inline constexpr unsigned iso_encoding() const noexcept { return __wd == 0u ? 7 : __wd; }
   inline constexpr bool ok() const noexcept { return __wd <= 6; }
          constexpr weekday_indexed operator[](unsigned __index) const noexcept;
          constexpr weekday_last    operator[](last_spec) const noexcept;
 
+  // TODO: Make private?
   static constexpr unsigned char __weekday_from_days(int __days) noexcept;
 };
 
 
 // https://howardhinnant.github.io/date_algorithms.html#weekday_from_days
 inline constexpr
 unsigned char weekday::__weekday_from_days(int __days) noexcept
 {
public:
     inline constexpr unsigned                          index() const noexcept { return __wdi.index(); }
     inline constexpr chrono::weekday_indexed weekday_indexed() const noexcept { return __wdi; }
 
     inline constexpr                       operator sys_days() const noexcept { return   sys_days{__to_days()}; }
     inline explicit constexpr operator            local_days() const noexcept { return local_days{__to_days()}; }
     inline constexpr bool ok() const noexcept
     {
         if (!__y.ok() || !__m.ok() || !__wdi.ok()) return false;
-    //  TODO: make sure it's a valid date
-        return true;
+        if (__wdi.index() <= 4) return true;
+        auto __nth_weekday_day =
+            __wdi.weekday() -
+            chrono::weekday{static_cast<sys_days>(__y / __m / 1)} +
+            days{(__wdi.index() - 1) * 7 + 1};
+        return static_cast<unsigned>(__nth_weekday_day.count()) <=
+               static_cast<unsigned>((__y / __m / last).day());
     }
 
     static constexpr year_month_weekday __from_days(days __d) noexcept;
     constexpr days __to_days() const noexcept;
 };
 
 inline constexpr
 year_month_weekday year_month_weekday::__from_days(days __d) noexcept

libcxx/test/std/utilities/time/time.cal/time.cal.ymwd/time.cal.ymwd.members/ok.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++98, c++03, c++11, c++14, c++17
 
 // <chrono>
 // class year_month_weekday;
 
 // constexpr bool ok() const noexcept;
-//  Returns: m_.ok() && y_.ok().
+//  Returns: If any of y_­.ok(), m_­.ok(), or wdi_­.ok() is false, returns false.
+//           Otherwise, if *this represents a valid date, returns true.
+//           Otherwise, returns false.
 
 #include <chrono>
 #include <type_traits>
 #include <cassert>
 
 #include "test_macros.h"
 
 int main(int, char**)
 {
     using year               = std::chrono::year;
     using month              = std::chrono::month;
     using weekday            = std::chrono::weekday;
     using weekday_indexed    = std::chrono::weekday_indexed;
     using year_month_weekday = std::chrono::year_month_weekday;
 
-    constexpr month January = std::chrono::January;
-    constexpr weekday Tuesday = std::chrono::Tuesday;
+    constexpr month January     = std::chrono::January;
+    constexpr weekday Monday    = std::chrono::Monday;
+    constexpr weekday Tuesday   = std::chrono::Tuesday;
+    constexpr weekday Wednesday = std::chrono::Wednesday;
+    constexpr weekday Thursday  = std::chrono::Thursday;
+    constexpr weekday Friday    = std::chrono::Friday;
+    constexpr weekday Saturday  = std::chrono::Saturday;
+    constexpr weekday Sunday    = std::chrono::Sunday;
 
     ASSERT_NOEXCEPT(                std::declval<const year_month_weekday>().ok());
     ASSERT_SAME_TYPE(bool, decltype(std::declval<const year_month_weekday>().ok()));
 
     static_assert(!year_month_weekday{}.ok(), "");
 
     static_assert(!year_month_weekday{year{-32768}, month{}, weekday_indexed{}}.ok(),           ""); // All three bad
 
     static_assert(!year_month_weekday{year{-32768}, January, weekday_indexed{Tuesday, 1}}.ok(), ""); // Bad year
     static_assert(!year_month_weekday{year{2019},   month{}, weekday_indexed{Tuesday, 1}}.ok(), ""); // Bad month
     static_assert(!year_month_weekday{year{2019},   January, weekday_indexed{} }.ok(),          ""); // Bad day
 
     static_assert(!year_month_weekday{year{-32768}, month{}, weekday_indexed{Tuesday, 1}}.ok(), ""); // Bad year & month
     static_assert(!year_month_weekday{year{2019},   month{}, weekday_indexed{} }.ok(),          ""); // Bad month & day
     static_assert(!year_month_weekday{year{-32768}, January, weekday_indexed{} }.ok(),          ""); // Bad year & day
 
+    static_assert(!year_month_weekday{year{2019},   January, weekday_indexed{Tuesday, static_cast<unsigned>(-1)}}.ok(), ""); // Bad index.
+    static_assert(!year_month_weekday{year{2019},   January, weekday_indexed{Wednesday, 0}}.ok(), "");                       // Bad index.
+
     static_assert( year_month_weekday{year{2019},   January, weekday_indexed{Tuesday, 1}}.ok(), ""); // All OK
+    static_assert( year_month_weekday{year{2019},   January, weekday_indexed{Tuesday, 4}}.ok(), ""); // All OK
+
+    static_assert(!year_month_weekday{year{2019},   January, weekday_indexed{Monday, 5}}.ok(),    ""); // Bad index
+    static_assert( year_month_weekday{year{2019},   January, weekday_indexed{Tuesday, 5}}.ok(),   ""); // All OK
+    static_assert( year_month_weekday{year{2019},   January, weekday_indexed{Wednesday, 5}}.ok(), ""); // All OK
+    static_assert( year_month_weekday{year{2019},   January, weekday_indexed{Thursday, 5}}.ok(),  ""); // All OK
+    static_assert(!year_month_weekday{year{2019},   January, weekday_indexed{Friday, 5}}.ok(),    ""); // Bad index
+    static_assert(!year_month_weekday{year{2019},   January, weekday_indexed{Saturday, 5}}.ok(),  ""); // Bad index
+    static_assert(!year_month_weekday{year{2019},   January, weekday_indexed{Sunday, 5}}.ok(),    ""); // Bad index
 
     for (unsigned i = 0; i <= 50; ++i)
     {
         year_month_weekday ym{year{2019}, January, weekday_indexed{Tuesday, i}};
         assert((ym.ok() == weekday_indexed{Tuesday, i}.ok()));
     }
 
     for (unsigned i = 0; i <= 50; ++i)