From 38a810023a87daede7e4caf2f7057832a1232558 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vojt=C4=9Bch=20Michal?= <vojta.michall@email.cz>
Date: Fri, 21 Nov 2025 08:08:04 +0100
Subject: [PATCH 01/13] Add tests

---
 .../test.cpp                                  | 317 ++++++++++++++----
 1 file changed, 252 insertions(+), 65 deletions(-)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
index 09cb4b1f4b2..2849b219271 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
@@ -15,86 +15,278 @@
 #include <is_permissive.hpp>
 #include <timezone_data.hpp>
 
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__);
+
 using namespace std;
 using namespace std::chrono;
 
-struct not_a_clock {
-    bool rep();
-    static char period;
-    int duration();
-    static float time_point;
-    using is_steady = long;
-    static int now;
+struct real_fake_clock {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
 };
 
-struct real_fake_clock {
-    using rep        = bool;
-    using period     = char;
-    using duration   = float;
-    using time_point = int;
-    static long is_steady;
-    static short now();
+struct rep_missing {
+
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
+};
+
+struct rep_not_type {
+    char rep;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
+};
+
+struct rep_wrong_type {
+    using rep                       = real_fake_clock;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
+};
+
+struct period_missing {
+    using rep = long long;
+
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
 };
 
-struct no_rep {
-    using period     = char;
-    using duration   = float;
-    using time_point = int;
-    static long is_steady;
-    static short now();
+struct period_not_type {
+    using rep = long long;
+    char period;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
 };
 
-struct no_period {
-    using rep        = bool;
-    using duration   = float;
-    using time_point = int;
-    static long is_steady;
-    static short now();
+struct period_wrong_type {
+    using rep                       = long long;
+    using period                    = char;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
 };
 
-struct no_duration {
-    using rep        = bool;
-    using period     = char;
-    using time_point = int;
-    static long is_steady;
-    static short now();
+struct duration_missing {
+    using rep    = long long;
+    using period = micro;
+
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
+};
+
+struct duration_not_type {
+    using rep    = long long;
+    using period = micro;
+    char duration;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
 };
 
-struct no_time_point {
-    using rep      = bool;
-    using period   = char;
-    using duration = float;
-    static long is_steady;
-    static short now();
+struct duration_wrong_type {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = int;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
 };
 
-struct no_steady {
-    using rep        = bool;
-    using period     = char;
-    using duration   = float;
-    using time_point = int;
-    static short now();
+struct duration_slightly_wrong_type {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = milliseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
 };
 
-struct no_now {
-    using rep        = bool;
-    using period     = char;
-    using duration   = float;
-    using time_point = int;
-    static long is_steady;
+struct duration_slightly_wrong_type2 {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = duration<int, micro>;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now();
 };
 
-static_assert(is_clock<steady_clock>::value, "steady_clock is not a clock");
-static_assert(is_clock_v<steady_clock>, "steady_clock is not a clock");
-static_assert(is_clock_v<real_fake_clock>, "real_fake_clock is not a clock");
-static_assert(!is_clock_v<not_a_clock>, "not_a_clock is a clock");
+struct time_point_missing {
+    using rep      = long long;
+    using period   = micro;
+    using duration = microseconds;
+
+    constexpr static bool is_steady = false;
+    static time_point<time_point_missing> now();
+};
+
+struct time_point_not_type {
+    using rep      = long long;
+    using period   = micro;
+    using duration = microseconds;
+    char time_point;
+    constexpr static bool is_steady = false;
+    static chrono::time_point<time_point_not_type> now();
+};
+
+struct time_point_wrong_type {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = int;
+    constexpr static bool is_steady = false;
+    static time_point now();
+};
+
+struct time_point_wrong_type2 {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock, nanoseconds>;
+    constexpr static bool is_steady = false;
+    static time_point now();
+};
+
+struct time_point_different_clock_ok {
+    using rep                       = long long;
+    using period                    = milli;
+    using duration                  = milliseconds;
+    using time_point                = time_point<real_fake_clock, milliseconds>;
+    constexpr static bool is_steady = false;
+    static time_point now();
+};
+
+struct is_steady_missing {
+    using rep        = long long;
+    using period     = micro;
+    using duration   = microseconds;
+    using time_point = time_point<real_fake_clock>;
+
+    static time_point now();
+};
+
+struct is_steady_type {
+    using rep        = long long;
+    using period     = micro;
+    using duration   = microseconds;
+    using time_point = time_point<real_fake_clock>;
+    using is_steady  = bool;
+    static time_point now();
+};
+
+struct is_steady_member {
+    using rep        = long long;
+    using period     = micro;
+    using duration   = microseconds;
+    using time_point = time_point<real_fake_clock>;
+    bool is_steady;
+    static time_point now();
+};
+
+struct now_missing {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+};
+
+struct now_type {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    using now                       = time_point;
+};
+
+struct now_not_fun {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static time_point now;
+};
+
+struct now_not_static {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    time_point now();
+};
+
+struct now_wrong_type {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<real_fake_clock>;
+    constexpr static bool is_steady = false;
+    static duration now();
+};
+
+// Check standard clocks
+STATIC_ASSERT(is_clock<steady_clock>::value);
+STATIC_ASSERT(is_clock_v<system_clock>);
+STATIC_ASSERT(is_clock_v<steady_clock>);
+STATIC_ASSERT(is_clock_v<high_resolution_clock>);
+STATIC_ASSERT(is_clock_v<utc_clock>);
+STATIC_ASSERT(is_clock_v<tai_clock>);
+STATIC_ASSERT(is_clock_v<gps_clock>);
+STATIC_ASSERT(is_clock_v<file_clock>);
+
+// Check custom clocks
+STATIC_ASSERT(is_clock_v<real_fake_clock>);
+
+STATIC_ASSERT(!is_clock_v<rep_missing>);
+STATIC_ASSERT(!is_clock_v<rep_not_type>);
+STATIC_ASSERT(!is_clock_v<rep_wrong_type>);
+
+STATIC_ASSERT(!is_clock_v<period_missing>);
+STATIC_ASSERT(!is_clock_v<period_not_type>);
+STATIC_ASSERT(!is_clock_v<period_wrong_type>);
+
+STATIC_ASSERT(!is_clock_v<duration_missing>);
+STATIC_ASSERT(!is_clock_v<duration_not_type>);
+STATIC_ASSERT(!is_clock_v<duration_wrong_type>);
+STATIC_ASSERT(!is_clock_v<duration_slightly_wrong_type>);
+STATIC_ASSERT(!is_clock_v<duration_slightly_wrong_type2>);
+
+STATIC_ASSERT(!is_clock_v<time_point_missing>);
+STATIC_ASSERT(!is_clock_v<time_point_not_type>);
+STATIC_ASSERT(!is_clock_v<time_point_wrong_type>);
+STATIC_ASSERT(!is_clock_v<time_point_wrong_type2>);
+STATIC_ASSERT(is_clock_v<time_point_different_clock_ok>);
+
+STATIC_ASSERT(!is_clock_v<is_steady_missing>);
+STATIC_ASSERT(!is_clock_v<is_steady_type>);
+STATIC_ASSERT(!is_clock_v<is_steady_member>);
+
+STATIC_ASSERT(!is_clock_v<now_missing>);
+STATIC_ASSERT(!is_clock_v<now_type>);
+STATIC_ASSERT(!is_clock_v<now_not_fun>);
+STATIC_ASSERT(!is_clock_v<now_not_static>);
+STATIC_ASSERT(!is_clock_v<now_wrong_type>);
 
-static_assert(!is_clock_v<no_rep>, "no_rep is a clock");
-static_assert(!is_clock_v<no_period>, "no_period is a clock");
-static_assert(!is_clock_v<no_duration>, "no_duration is a clock");
-static_assert(!is_clock_v<no_time_point>, "no_time_point is a clock");
-static_assert(!is_clock_v<no_steady>, "no_steady is a clock");
-static_assert(!is_clock_v<no_now>, "no_now is a clock");
 
 void test_is_leap_second(const year_month_day& ymd) {
     const sys_days ls{ymd};
@@ -376,11 +568,6 @@ void test_clock_cast() {
     assert(clock_cast<utc_clock>(sys_seconds{sys_days{2000y / January / 1}}).time_since_epoch() == 946'684'822s);
 }
 
-static_assert(is_clock_v<utc_clock>);
-static_assert(is_clock_v<tai_clock>);
-static_assert(is_clock_v<gps_clock>);
-static_assert(is_clock_v<file_clock>);
-
 tzdb copy_tzdb() {
     const auto& my_tzdb = get_tzdb_list().front();
     vector<time_zone> zones;

From 68b732cec4f5be2372b9263c2a5f53536cf590c0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vojt=C4=9Bch=20Michal?= <vojta.michall@email.cz>
Date: Fri, 21 Nov 2025 08:09:22 +0100
Subject: [PATCH 02/13] Perform additional (stricter) checks in
 std::chrono::is_clock_v

---
 stl/inc/__msvc_chrono.hpp | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/stl/inc/__msvc_chrono.hpp b/stl/inc/__msvc_chrono.hpp
index 094f700699d..540f2d109ed 100644
--- a/stl/inc/__msvc_chrono.hpp
+++ b/stl/inc/__msvc_chrono.hpp
@@ -58,15 +58,32 @@ namespace chrono {
         }
     };
 
+    _EXPORT_STD template <class _Rep, class _Period = ratio<1>>
+    class duration;
+
+    _EXPORT_STD template <class _Clock, class _Duration = typename _Clock::duration>
+    class time_point;
+
 #if _HAS_CXX20
     _EXPORT_STD template <class _Clock>
     _NO_SPECIALIZATIONS_OF_VARIABLE_TEMPLATES constexpr bool is_clock_v = requires {
+        // Basic checks from https://eel.is/c++draft/time.traits.is.clock#1
         typename _Clock::rep;
         typename _Clock::period;
         typename _Clock::duration;
         typename _Clock::time_point;
         _Clock::is_steady;
         _Clock::now();
+
+        // Complete checks from https://eel.is/c++draft/tab:time.clock
+        // "An arithmetic type or a class emulating an arithmetic type" is not checked
+        requires _Is_ratio_v<typename _Clock::period>;
+        requires same_as<typename _Clock::duration, duration<typename _Clock::rep, typename _Clock::period>>;
+        requires same_as<typename _Clock::time_point, time_point<_Clock>>
+                     || same_as<typename _Clock::time_point,
+                         time_point<typename _Clock::time_point::clock, typename _Clock::duration>>;
+        { _Clock::is_steady } -> std::same_as<const bool&>;
+        { _Clock::now() } -> std::same_as<typename _Clock::time_point>;
     };
     _EXPORT_STD template <class _Clock>
     struct _NO_SPECIALIZATIONS_CITING("N5014 [time.traits.is.clock]/2") is_clock : bool_constant<is_clock_v<_Clock>> {};
@@ -84,9 +101,6 @@ namespace chrono {
             true;
 #endif // ^^^ !_HAS_CXX20 ^^^
 
-    _EXPORT_STD template <class _Rep, class _Period = ratio<1>>
-    class duration;
-
     template <class _Ty>
     constexpr bool _Is_duration_v = _Is_specialization_v<_Ty, duration>;
 
@@ -203,7 +217,7 @@ namespace chrono {
         _Rep _MyRep; // the stored rep
     };
 
-    _EXPORT_STD template <class _Clock, class _Duration = typename _Clock::duration>
+    _EXPORT_STD template <class _Clock, class _Duration>
     class time_point { // represents a point in time
     public:
         using clock    = _Clock;

From 8417029f1e078196fafc90cf93a59a022d27e811 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vojt=C4=9Bch=20Michal?= <vojta.michall@email.cz>
Date: Fri, 21 Nov 2025 08:16:33 +0100
Subject: [PATCH 03/13] Replace _Clock::now() with _Clock::now to reject
 typedefs

---
 stl/inc/__msvc_chrono.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/stl/inc/__msvc_chrono.hpp b/stl/inc/__msvc_chrono.hpp
index 540f2d109ed..9dfffb642f1 100644
--- a/stl/inc/__msvc_chrono.hpp
+++ b/stl/inc/__msvc_chrono.hpp
@@ -73,7 +73,7 @@ namespace chrono {
         typename _Clock::duration;
         typename _Clock::time_point;
         _Clock::is_steady;
-        _Clock::now();
+        _Clock::now;
 
         // Complete checks from https://eel.is/c++draft/tab:time.clock
         // "An arithmetic type or a class emulating an arithmetic type" is not checked

From aeeea02e4ca1132ecc0ad6a55ad46496c62b97e0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vojt=C4=9Bch=20Michal?= <vojta.michall@email.cz>
Date: Fri, 21 Nov 2025 08:52:44 +0100
Subject: [PATCH 04/13] Replace links in comments with proper reference to the
 standard

---
 stl/inc/__msvc_chrono.hpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/stl/inc/__msvc_chrono.hpp b/stl/inc/__msvc_chrono.hpp
index 9dfffb642f1..105766a52f0 100644
--- a/stl/inc/__msvc_chrono.hpp
+++ b/stl/inc/__msvc_chrono.hpp
@@ -67,7 +67,7 @@ namespace chrono {
 #if _HAS_CXX20
     _EXPORT_STD template <class _Clock>
     _NO_SPECIALIZATIONS_OF_VARIABLE_TEMPLATES constexpr bool is_clock_v = requires {
-        // Basic checks from https://eel.is/c++draft/time.traits.is.clock#1
+        // Basic checks from N5014 [time.traits.is.clock] / 1 
         typename _Clock::rep;
         typename _Clock::period;
         typename _Clock::duration;
@@ -75,7 +75,7 @@ namespace chrono {
         _Clock::is_steady;
         _Clock::now;
 
-        // Complete checks from https://eel.is/c++draft/tab:time.clock
+        // Additional stricter checks from N5014 [time.clock.req] / 2
         // "An arithmetic type or a class emulating an arithmetic type" is not checked
         requires _Is_ratio_v<typename _Clock::period>;
         requires same_as<typename _Clock::duration, duration<typename _Clock::rep, typename _Clock::period>>;

From 290c5eba1f15a1251e4cbe8916ffdc218dcccb66 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vojt=C4=9Bch=20Michal?= <vojta.michall@email.cz>
Date: Fri, 21 Nov 2025 10:09:43 +0100
Subject: [PATCH 05/13] Correct endline character

---
 stl/inc/__msvc_chrono.hpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/stl/inc/__msvc_chrono.hpp b/stl/inc/__msvc_chrono.hpp
index 105766a52f0..55caba6382c 100644
--- a/stl/inc/__msvc_chrono.hpp
+++ b/stl/inc/__msvc_chrono.hpp
@@ -67,7 +67,7 @@ namespace chrono {
 #if _HAS_CXX20
     _EXPORT_STD template <class _Clock>
     _NO_SPECIALIZATIONS_OF_VARIABLE_TEMPLATES constexpr bool is_clock_v = requires {
-        // Basic checks from N5014 [time.traits.is.clock] / 1 
+        // Basic checks from N5014 [time.traits.is.clock]/1
         typename _Clock::rep;
         typename _Clock::period;
         typename _Clock::duration;
@@ -75,7 +75,7 @@ namespace chrono {
         _Clock::is_steady;
         _Clock::now;
 
-        // Additional stricter checks from N5014 [time.clock.req] / 2
+        // Additional stricter checks from N5014 [time.clock.req]/2
         // "An arithmetic type or a class emulating an arithmetic type" is not checked
         requires _Is_ratio_v<typename _Clock::period>;
         requires same_as<typename _Clock::duration, duration<typename _Clock::rep, typename _Clock::period>>;

From a14115e386d4c177e83fc0794ecd6176f31f690c Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 25 Nov 2025 08:57:48 -0800
Subject: [PATCH 06/13] `T::now()` is part of the basic checks.

---
 stl/inc/__msvc_chrono.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/stl/inc/__msvc_chrono.hpp b/stl/inc/__msvc_chrono.hpp
index 55caba6382c..cdf2030242a 100644
--- a/stl/inc/__msvc_chrono.hpp
+++ b/stl/inc/__msvc_chrono.hpp
@@ -73,7 +73,7 @@ namespace chrono {
         typename _Clock::duration;
         typename _Clock::time_point;
         _Clock::is_steady;
-        _Clock::now;
+        _Clock::now();
 
         // Additional stricter checks from N5014 [time.clock.req]/2
         // "An arithmetic type or a class emulating an arithmetic type" is not checked

From f4de01a8bb74c8d2d63619e2ce6c7fb31e90b056 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 25 Nov 2025 09:08:26 -0800
Subject: [PATCH 07/13] Remove unnecessary newlines.

---
 .../test.cpp                                   | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
index 2849b219271..a5c7619f68f 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
@@ -30,7 +30,6 @@ struct real_fake_clock {
 };
 
 struct rep_missing {
-
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
@@ -57,8 +56,7 @@ struct rep_wrong_type {
 };
 
 struct period_missing {
-    using rep = long long;
-
+    using rep                       = long long;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
     constexpr static bool is_steady = false;
@@ -84,9 +82,8 @@ struct period_wrong_type {
 };
 
 struct duration_missing {
-    using rep    = long long;
-    using period = micro;
-
+    using rep                       = long long;
+    using period                    = micro;
     using time_point                = time_point<real_fake_clock>;
     constexpr static bool is_steady = false;
     static time_point now();
@@ -129,10 +126,9 @@ struct duration_slightly_wrong_type2 {
 };
 
 struct time_point_missing {
-    using rep      = long long;
-    using period   = micro;
-    using duration = microseconds;
-
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = microseconds;
     constexpr static bool is_steady = false;
     static time_point<time_point_missing> now();
 };
@@ -178,7 +174,6 @@ struct is_steady_missing {
     using period     = micro;
     using duration   = microseconds;
     using time_point = time_point<real_fake_clock>;
-
     static time_point now();
 };
 
@@ -287,7 +282,6 @@ STATIC_ASSERT(!is_clock_v<now_not_fun>);
 STATIC_ASSERT(!is_clock_v<now_not_static>);
 STATIC_ASSERT(!is_clock_v<now_wrong_type>);
 
-
 void test_is_leap_second(const year_month_day& ymd) {
     const sys_days ls{ymd};
     const auto& leap_seconds = get_tzdb().leap_seconds;

From 62663570e49d73787f0606b81bc409809261c895 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 25 Nov 2025 09:15:02 -0800
Subject: [PATCH 08/13] Use terse `static_assert` in C++20.

---
 .../test.cpp                                  | 80 +++++++++----------
 1 file changed, 39 insertions(+), 41 deletions(-)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
index a5c7619f68f..dbb9367fa1c 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
@@ -15,8 +15,6 @@
 #include <is_permissive.hpp>
 #include <timezone_data.hpp>
 
-#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__);
-
 using namespace std;
 using namespace std::chrono;
 
@@ -240,47 +238,47 @@ struct now_wrong_type {
 };
 
 // Check standard clocks
-STATIC_ASSERT(is_clock<steady_clock>::value);
-STATIC_ASSERT(is_clock_v<system_clock>);
-STATIC_ASSERT(is_clock_v<steady_clock>);
-STATIC_ASSERT(is_clock_v<high_resolution_clock>);
-STATIC_ASSERT(is_clock_v<utc_clock>);
-STATIC_ASSERT(is_clock_v<tai_clock>);
-STATIC_ASSERT(is_clock_v<gps_clock>);
-STATIC_ASSERT(is_clock_v<file_clock>);
+static_assert(is_clock<steady_clock>::value);
+static_assert(is_clock_v<system_clock>);
+static_assert(is_clock_v<steady_clock>);
+static_assert(is_clock_v<high_resolution_clock>);
+static_assert(is_clock_v<utc_clock>);
+static_assert(is_clock_v<tai_clock>);
+static_assert(is_clock_v<gps_clock>);
+static_assert(is_clock_v<file_clock>);
 
 // Check custom clocks
-STATIC_ASSERT(is_clock_v<real_fake_clock>);
-
-STATIC_ASSERT(!is_clock_v<rep_missing>);
-STATIC_ASSERT(!is_clock_v<rep_not_type>);
-STATIC_ASSERT(!is_clock_v<rep_wrong_type>);
-
-STATIC_ASSERT(!is_clock_v<period_missing>);
-STATIC_ASSERT(!is_clock_v<period_not_type>);
-STATIC_ASSERT(!is_clock_v<period_wrong_type>);
-
-STATIC_ASSERT(!is_clock_v<duration_missing>);
-STATIC_ASSERT(!is_clock_v<duration_not_type>);
-STATIC_ASSERT(!is_clock_v<duration_wrong_type>);
-STATIC_ASSERT(!is_clock_v<duration_slightly_wrong_type>);
-STATIC_ASSERT(!is_clock_v<duration_slightly_wrong_type2>);
-
-STATIC_ASSERT(!is_clock_v<time_point_missing>);
-STATIC_ASSERT(!is_clock_v<time_point_not_type>);
-STATIC_ASSERT(!is_clock_v<time_point_wrong_type>);
-STATIC_ASSERT(!is_clock_v<time_point_wrong_type2>);
-STATIC_ASSERT(is_clock_v<time_point_different_clock_ok>);
-
-STATIC_ASSERT(!is_clock_v<is_steady_missing>);
-STATIC_ASSERT(!is_clock_v<is_steady_type>);
-STATIC_ASSERT(!is_clock_v<is_steady_member>);
-
-STATIC_ASSERT(!is_clock_v<now_missing>);
-STATIC_ASSERT(!is_clock_v<now_type>);
-STATIC_ASSERT(!is_clock_v<now_not_fun>);
-STATIC_ASSERT(!is_clock_v<now_not_static>);
-STATIC_ASSERT(!is_clock_v<now_wrong_type>);
+static_assert(is_clock_v<real_fake_clock>);
+
+static_assert(!is_clock_v<rep_missing>);
+static_assert(!is_clock_v<rep_not_type>);
+static_assert(!is_clock_v<rep_wrong_type>);
+
+static_assert(!is_clock_v<period_missing>);
+static_assert(!is_clock_v<period_not_type>);
+static_assert(!is_clock_v<period_wrong_type>);
+
+static_assert(!is_clock_v<duration_missing>);
+static_assert(!is_clock_v<duration_not_type>);
+static_assert(!is_clock_v<duration_wrong_type>);
+static_assert(!is_clock_v<duration_slightly_wrong_type>);
+static_assert(!is_clock_v<duration_slightly_wrong_type2>);
+
+static_assert(!is_clock_v<time_point_missing>);
+static_assert(!is_clock_v<time_point_not_type>);
+static_assert(!is_clock_v<time_point_wrong_type>);
+static_assert(!is_clock_v<time_point_wrong_type2>);
+static_assert(is_clock_v<time_point_different_clock_ok>);
+
+static_assert(!is_clock_v<is_steady_missing>);
+static_assert(!is_clock_v<is_steady_type>);
+static_assert(!is_clock_v<is_steady_member>);
+
+static_assert(!is_clock_v<now_missing>);
+static_assert(!is_clock_v<now_type>);
+static_assert(!is_clock_v<now_not_fun>);
+static_assert(!is_clock_v<now_not_static>);
+static_assert(!is_clock_v<now_wrong_type>);
 
 void test_is_leap_second(const year_month_day& ymd) {
     const sys_days ls{ymd};

From e9b070dbf92b26f3c247c3d96367b1b8736afe5d Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 25 Nov 2025 09:22:08 -0800
Subject: [PATCH 09/13] Include `<ratio>`.

---
 tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
index dbb9367fa1c..bb816ffa1a0 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
@@ -9,6 +9,7 @@
 #include <filesystem>
 #include <functional>
 #include <iterator>
+#include <ratio>
 #include <type_traits>
 #include <utility>
 

From dce37e0fcc07c1cbcac821b2e1bed11d4d540609 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 25 Nov 2025 09:24:19 -0800
Subject: [PATCH 10/13] `constexpr static` => `static constexpr`

---
 .../test.cpp                                  | 44 +++++++++----------
 1 file changed, 22 insertions(+), 22 deletions(-)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
index bb816ffa1a0..c1a44bd84f4 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
@@ -24,7 +24,7 @@ struct real_fake_clock {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -32,7 +32,7 @@ struct rep_missing {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -41,7 +41,7 @@ struct rep_not_type {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -50,7 +50,7 @@ struct rep_wrong_type {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -58,7 +58,7 @@ struct period_missing {
     using rep                       = long long;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -67,7 +67,7 @@ struct period_not_type {
     char period;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -76,7 +76,7 @@ struct period_wrong_type {
     using period                    = char;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -84,7 +84,7 @@ struct duration_missing {
     using rep                       = long long;
     using period                    = micro;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -93,7 +93,7 @@ struct duration_not_type {
     using period = micro;
     char duration;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -102,7 +102,7 @@ struct duration_wrong_type {
     using period                    = micro;
     using duration                  = int;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -111,7 +111,7 @@ struct duration_slightly_wrong_type {
     using period                    = micro;
     using duration                  = milliseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -120,7 +120,7 @@ struct duration_slightly_wrong_type2 {
     using period                    = micro;
     using duration                  = duration<int, micro>;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -128,7 +128,7 @@ struct time_point_missing {
     using rep                       = long long;
     using period                    = micro;
     using duration                  = microseconds;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point<time_point_missing> now();
 };
 
@@ -137,7 +137,7 @@ struct time_point_not_type {
     using period   = micro;
     using duration = microseconds;
     char time_point;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static chrono::time_point<time_point_not_type> now();
 };
 
@@ -146,7 +146,7 @@ struct time_point_wrong_type {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = int;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -155,7 +155,7 @@ struct time_point_wrong_type2 {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock, nanoseconds>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -164,7 +164,7 @@ struct time_point_different_clock_ok {
     using period                    = milli;
     using duration                  = milliseconds;
     using time_point                = time_point<real_fake_clock, milliseconds>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now();
 };
 
@@ -199,7 +199,7 @@ struct now_missing {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
 };
 
 struct now_type {
@@ -207,7 +207,7 @@ struct now_type {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     using now                       = time_point;
 };
 
@@ -216,7 +216,7 @@ struct now_not_fun {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static time_point now;
 };
 
@@ -225,7 +225,7 @@ struct now_not_static {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     time_point now();
 };
 
@@ -234,7 +234,7 @@ struct now_wrong_type {
     using period                    = micro;
     using duration                  = microseconds;
     using time_point                = time_point<real_fake_clock>;
-    constexpr static bool is_steady = false;
+    static constexpr bool is_steady = false;
     static duration now();
 };
 

From 960d51c128402bda42572577f9ac622963202c11 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 25 Nov 2025 09:59:33 -0800
Subject: [PATCH 11/13] `is_steady_member` => `is_steady_not_static`

---
 .../tests/P0355R7_calendars_and_time_zones_clocks/test.cpp    | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
index c1a44bd84f4..beb21099553 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
@@ -185,7 +185,7 @@ struct is_steady_type {
     static time_point now();
 };
 
-struct is_steady_member {
+struct is_steady_not_static {
     using rep        = long long;
     using period     = micro;
     using duration   = microseconds;
@@ -273,7 +273,7 @@ static_assert(is_clock_v<time_point_different_clock_ok>);
 
 static_assert(!is_clock_v<is_steady_missing>);
 static_assert(!is_clock_v<is_steady_type>);
-static_assert(!is_clock_v<is_steady_member>);
+static_assert(!is_clock_v<is_steady_not_static>);
 
 static_assert(!is_clock_v<now_missing>);
 static_assert(!is_clock_v<now_type>);

From e350ce8bfad9ccdd55af079b6ab567095007db0d Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 25 Nov 2025 10:09:00 -0800
Subject: [PATCH 12/13] Add `time_point_wrong_type3`, `is_steady_wrong_type`.

---
 .../test.cpp                                  | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
index beb21099553..3cc7ea83fa9 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
@@ -159,6 +159,15 @@ struct time_point_wrong_type2 {
     static time_point now();
 };
 
+struct time_point_wrong_type3 {
+    using rep                       = long long;
+    using period                    = micro;
+    using duration                  = microseconds;
+    using time_point                = time_point<time_point_wrong_type3, nanoseconds>;
+    static constexpr bool is_steady = false;
+    static time_point now();
+};
+
 struct time_point_different_clock_ok {
     using rep                       = long long;
     using period                    = milli;
@@ -194,6 +203,15 @@ struct is_steady_not_static {
     static time_point now();
 };
 
+struct is_steady_wrong_type {
+    using rep                      = long long;
+    using period                   = micro;
+    using duration                 = microseconds;
+    using time_point               = time_point<real_fake_clock>;
+    static constexpr int is_steady = 0;
+    static time_point now();
+};
+
 struct now_missing {
     using rep                       = long long;
     using period                    = micro;
@@ -269,11 +287,13 @@ static_assert(!is_clock_v<time_point_missing>);
 static_assert(!is_clock_v<time_point_not_type>);
 static_assert(!is_clock_v<time_point_wrong_type>);
 static_assert(!is_clock_v<time_point_wrong_type2>);
+static_assert(!is_clock_v<time_point_wrong_type3>);
 static_assert(is_clock_v<time_point_different_clock_ok>);
 
 static_assert(!is_clock_v<is_steady_missing>);
 static_assert(!is_clock_v<is_steady_type>);
 static_assert(!is_clock_v<is_steady_not_static>);
+static_assert(!is_clock_v<is_steady_wrong_type>);
 
 static_assert(!is_clock_v<now_missing>);
 static_assert(!is_clock_v<now_type>);

From c5ba2a8fa8c2649b339ec08fa65a14ae03321feb Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 25 Nov 2025 10:51:33 -0800
Subject: [PATCH 13/13] Reported VSO-2649325 "C1XX incorrectly handles
 `requires { C::now(); }` when `now` is a type".

---
 .../std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp  | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
index 3cc7ea83fa9..8a2af4a0d1a 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_clocks/test.cpp
@@ -296,7 +296,9 @@ static_assert(!is_clock_v<is_steady_not_static>);
 static_assert(!is_clock_v<is_steady_wrong_type>);
 
 static_assert(!is_clock_v<now_missing>);
+#if defined(__clang__) || defined(__EDG__) // TRANSITION, VSO-2649325
 static_assert(!is_clock_v<now_type>);
+#endif // ^^^ no workaround ^^^
 static_assert(!is_clock_v<now_not_fun>);
 static_assert(!is_clock_v<now_not_static>);
 static_assert(!is_clock_v<now_wrong_type>);