[libc++] Refactor some .fail.cpp tests and fix time_point_cast not SFINAEing away

libcxx/include/__chrono/time_point.h

@@ -95,7 +95,7 @@ struct common_type<chrono::time_point<_Clock, _Duration1>, chrono::time_point<_C
 
 namespace chrono {
 
-template <class _ToDuration, class _Clock, class _Duration>
+template <class _ToDuration, class _Clock, class _Duration, __enable_if_t<__is_duration_v<_ToDuration>, int> = 0>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 time_point<_Clock, _ToDuration>
 time_point_cast(const time_point<_Clock, _Duration>& __t) {
   return time_point<_Clock, _ToDuration>(chrono::duration_cast<_ToDuration>(__t.time_since_epoch()));

libcxx/include/__cxx03/__chrono/time_point.h

@@ -81,7 +81,7 @@ common_type<chrono::time_point<_Clock, _Duration1>, chrono::time_point<_Clock, _
 
 namespace chrono {
 
-template <class _ToDuration, class _Clock, class _Duration>
+template <class _ToDuration, class _Clock, class _Duration, __enable_if_t<__is_duration<_ToDuration>::value, int> = 0>
 inline _LIBCPP_HIDE_FROM_ABI time_point<_Clock, _ToDuration> time_point_cast(const time_point<_Clock, _Duration>& __t) {
   return time_point<_Clock, _ToDuration>(chrono::duration_cast<_ToDuration>(__t.time_since_epoch()));
 }

libcxx/test/std/time/time.duration/time.duration.alg/abs.pass.cpp

@@ -19,9 +19,19 @@
 #include <cassert>
 #include <ratio>
 #include <type_traits>
+#include <utility>
 
 #include "test_macros.h"
 
+template <class T, class = void>
+inline constexpr bool has_abs_v = false;
+
+template <class T>
+inline constexpr bool has_abs_v<T, decltype((void)std::chrono::abs(std::declval<T>()))> = true;
+
+static_assert(has_abs_v<std::chrono::milliseconds>);
+static_assert(!has_abs_v<std::chrono::duration<unsigned>>);
+
 template <class Duration>
 void
 test(const Duration& f, const Duration& d)

libcxx/test/std/time/time.point/time.point.cast/ceil.pass.cpp

@@ -21,6 +21,15 @@
 
 #include "test_macros.h"
 
+template <class T, class = void>
+inline constexpr bool has_ceil_v = false;
+
+template <class T>
+inline constexpr bool has_ceil_v<T, decltype((void)std::chrono::ceil<T>(std::chrono::system_clock::now()))> = true;
+
+static_assert(has_ceil_v<std::chrono::seconds>);
+static_assert(!has_ceil_v<int>);
+
 template <class FromDuration, class ToDuration>
 void
 test(const FromDuration& df, const ToDuration& d)

libcxx/test/std/time/time.point/time.point.cast/floor.pass.cpp

@@ -21,6 +21,15 @@
 
 #include "test_macros.h"
 
+template <class T, class = void>
+inline constexpr bool has_floor_v = false;
+
+template <class T>
+inline constexpr bool has_floor_v<T, decltype((void)std::chrono::floor<T>(std::chrono::system_clock::now()))> = true;
+
+static_assert(has_floor_v<std::chrono::seconds>);
+static_assert(!has_floor_v<int>);
+
 template <class FromDuration, class ToDuration>
 void
 test(const FromDuration& df, const ToDuration& d)

libcxx/test/std/time/time.point/time.point.cast/round.pass.cpp

@@ -21,6 +21,15 @@
 
 #include "test_macros.h"
 
+template <class T, class = void>
+inline constexpr bool has_round_v = false;
+
+template <class T>
+inline constexpr bool has_round_v<T, decltype((void)std::chrono::round<T>(std::chrono::system_clock::now()))> = true;
+
+static_assert(has_round_v<std::chrono::seconds>);
+static_assert(!has_round_v<int>);
+
 template <class FromDuration, class ToDuration>
 void
 test(const FromDuration& df, const ToDuration& d)

libcxx/test/std/time/time.point/time.point.cast/time_point_cast.pass.cpp

@@ -21,6 +21,16 @@
 
 #include "test_macros.h"
 
+template <class T, class = void>
+struct has_time_point_cast : std::false_type {};
+
+template <class T>
+struct has_time_point_cast<T, decltype((void)std::chrono::time_point_cast<T>(std::chrono::system_clock::now()))>
+    : std::true_type {};
+
+static_assert(has_time_point_cast<std::chrono::seconds>::value, "");
+static_assert(!has_time_point_cast<int>::value, "");
+
 template <class FromDuration, class ToDuration>
 void
 test(const FromDuration& df, const ToDuration& d)