Fix JSON encoding of datetimes with zoneinfo tzinfos

This fixes a bug where datetime objects with `zoneinfo.ZoneInfo`
instances set for `tzinfo` would encode as UTC, ignoring the zoneinfo.
This issue was due to `datetime.utcoffset` being called with `None`
instead of the `datetime` instance. This worked fine for other `tzinfo`
types (like `datetime.timezone`) since those use fixed offsets that
aren't date aware.

This also fixes a bug where `datetime.time` instances with a `tzinfo`
that returns `None` from `datetime.time.utcoffset` were treated as UTC
rather than naive. Quoting from the standard library docs:

> A datetime object d is aware if both of the following hold:
>
> 1. d.tzinfo is not None
> 2. d.tzinfo.utcoffset(d) does not return None
>
> Otherwise, d is naive.
>
> A time object t is aware if both of the following hold:
>
> 1. t.tzinfo is not None
> 2. t.tzinfo.utcoffset(None) does not return None.
>
> Otherwise, t is naive.

Both bugs fixed above were due to incorrect behavior around the 2nd
condition using `utcoffset`.

msgspec/_core.c

@@ -9864,7 +9864,7 @@ ms_encode_date(PyObject *obj, char *out)
 /* Requires 21 bytes of scratch space */
 static int
 ms_encode_time_parts(
-    MsgspecState *mod, PyObject *obj,
+    MsgspecState *mod, PyObject *datetime_or_none,
     uint8_t hour, uint8_t minute, uint8_t second, uint32_t microsecond,
     PyObject *tzinfo, char *out, int out_offset
 ) {
@@ -9883,11 +9883,20 @@ ms_encode_time_parts(
         int32_t offset_days = 0, offset_secs = 0;
 
         if (tzinfo != PyDateTime_TimeZone_UTC) {
-            PyObject *offset = CALL_METHOD_ONE_ARG(tzinfo, mod->str_utcoffset, Py_None);
-            if (offset == NULL) return -1;
-            if (PyDelta_Check(offset)) {
+            PyObject *offset = CALL_METHOD_ONE_ARG(
+                tzinfo, mod->str_utcoffset, datetime_or_none
+            );
+            if (offset == NULL) {
+                return -1;
+            }
+            else if (PyDelta_Check(offset)) {
                 offset_days = PyDateTime_DELTA_GET_DAYS(offset);
                 offset_secs = PyDateTime_DELTA_GET_SECONDS(offset);
+                Py_DECREF(offset);
+            }
+            else if (offset == Py_None) {
+                Py_DECREF(offset);
+                goto done;
             }
             else if (offset != Py_None) {
                 PyErr_SetString(
@@ -9897,7 +9906,6 @@ ms_encode_time_parts(
                 Py_DECREF(offset);
                 return -1;
             }
-            Py_DECREF(offset);
         }
         if (MS_LIKELY(offset_secs == 0)) {
             *p++ = 'Z';
@@ -9935,6 +9943,8 @@ ms_encode_time_parts(
             }
         }
     }
+
+done:
     return p - out;
 }
 
@@ -9950,7 +9960,7 @@ ms_encode_time(MsgspecState *mod, PyObject *obj, char *out)
     uint32_t microsecond = PyDateTime_TIME_GET_MICROSECOND(obj);
     PyObject *tzinfo = MS_TIME_GET_TZINFO(obj);
     return ms_encode_time_parts(
-        mod, obj, hour, minute, second, microsecond, tzinfo, out, 0
+        mod, Py_None, hour, minute, second, microsecond, tzinfo, out, 0
     );
 }
 

tests/test_common.py

@@ -3164,6 +3164,18 @@ def test_encode_time_offset_rounds_to_nearest_minute(self, proto, offset, t_str)
         sol = proto.encode(t_str)
         assert res == sol
 
+    @py39_plus
+    def test_encode_time_zoneinfo(self):
+        import zoneinfo
+
+        try:
+            x = datetime.time(1, 2, 3, 456789, zoneinfo.ZoneInfo("America/Chicago"))
+        except zoneinfo.ZoneInfoNotFoundError:
+            pytest.skip(reason="Failed to load timezone")
+        sol = msgspec.json.encode(x.isoformat())
+        res = msgspec.json.encode(x)
+        assert res == sol
+
     @pytest.mark.parametrize(
         "dt",
         [

tests/test_json.py

@@ -33,6 +33,9 @@
 
 UTC = datetime.timezone.utc
 
+PY39 = sys.version_info[:2] >= (3, 9)
+py39_plus = pytest.mark.skipif(not PY39, reason="3.9+ only")
+
 
 class FruitInt(enum.IntEnum):
     APPLE = -1
@@ -838,6 +841,20 @@ def test_encode_datetime_offset_rounds_to_nearest_minute(self, offset, expected)
         s = msgspec.json.encode(x)
         assert s == expected
 
+    @py39_plus
+    def test_encode_datetime_zoneinfo(self):
+        import zoneinfo
+
+        try:
+            x = datetime.datetime(
+                2023, 1, 2, 3, 4, 5, 678, zoneinfo.ZoneInfo("America/Chicago")
+            )
+        except zoneinfo.ZoneInfoNotFoundError:
+            pytest.skip(reason="Failed to load timezone")
+        sol = msgspec.json.encode(x.isoformat())
+        res = msgspec.json.encode(x)
+        assert res == sol
+
     @pytest.mark.parametrize(
         "dt",
         [