fix: allow assignment of time points of resolutions other than that of a system clock (#2481)

include/pybind11/chrono.h

@@ -140,7 +140,7 @@ public:
         }
         else return false;
 
-        value = system_clock::from_time_t(std::mktime(&cal)) + msecs;
+        value = time_point_cast<Duration>(system_clock::from_time_t(std::mktime(&cal)) + msecs);
         return true;
     }
 

tests/test_chrono.cpp

@@ -12,6 +12,24 @@
 #include <pybind11/chrono.h>
 #include <chrono>
 
+struct different_resolutions {
+    using time_point_h = std::chrono::time_point<
+        std::chrono::system_clock, std::chrono::hours>;
+    using time_point_m = std::chrono::time_point<
+        std::chrono::system_clock, std::chrono::minutes>;
+    using time_point_s = std::chrono::time_point<
+        std::chrono::system_clock, std::chrono::seconds>;
+    using time_point_ms = std::chrono::time_point<
+        std::chrono::system_clock, std::chrono::milliseconds>;
+    using time_point_us = std::chrono::time_point<
+        std::chrono::system_clock, std::chrono::microseconds>;
+    time_point_h timestamp_h;
+    time_point_m timestamp_m;
+    time_point_s timestamp_s;
+    time_point_ms timestamp_ms;
+    time_point_us timestamp_us;
+};
+
 TEST_SUBMODULE(chrono, m) {
     using system_time = std::chrono::system_clock::time_point;
     using steady_time = std::chrono::steady_clock::time_point;
@@ -53,4 +71,14 @@ TEST_SUBMODULE(chrono, m) {
     m.def("test_nano_timepoint", [](timestamp start, timespan delta) -> timestamp {
         return start + delta;
     });
+
+    // Test different resolutions
+    py::class_<different_resolutions>(m, "different_resolutions")
+        .def(py::init<>())
+        .def_readwrite("timestamp_h", &different_resolutions::timestamp_h)
+        .def_readwrite("timestamp_m", &different_resolutions::timestamp_m)
+        .def_readwrite("timestamp_s", &different_resolutions::timestamp_s)
+        .def_readwrite("timestamp_ms", &different_resolutions::timestamp_ms)
+        .def_readwrite("timestamp_us", &different_resolutions::timestamp_us)
+        ;
 }

tests/test_chrono.py

@@ -200,3 +200,13 @@ def test_nano_timepoint():
     time = datetime.datetime.now()
     time1 = m.test_nano_timepoint(time, datetime.timedelta(seconds=60))
     assert(time1 == time + datetime.timedelta(seconds=60))
+
+
+def test_chrono_different_resolutions():
+    resolutions = m.different_resolutions()
+    time = datetime.datetime.now()
+    resolutions.timestamp_h = time
+    resolutions.timestamp_m = time
+    resolutions.timestamp_s = time
+    resolutions.timestamp_ms = time
+    resolutions.timestamp_us = time