Fix parse() crash on an ISO 8601 date + duration interval

When parse() is given an interval made of a duration and a date-only
endpoint (e.g. "2021-01-01/P1DT1H" or "P1Y/2021-01-01"), base_parse
returns a datetime.date for the endpoint, so pendulum.instance() returns a
Date. _parse then calls Date.add()/Date.subtract() with the duration's
hours/minutes/seconds/microseconds, which Date does not accept, raising
'TypeError: add() got an unexpected keyword argument 'hours''. Endpoints
that carry a time component return a DateTime and worked fine.

Promote a date-only endpoint to a midnight datetime before instance(), so
the interval has DateTime endpoints (matching the time-bearing case and the
function's Interval[DateTime] return type) and add()/subtract() accept the
time components. Fixes #881.

Author: vineethsaivs

src/pendulum/parser.py

@@ -36,6 +36,18 @@ def parse(text: str, **options: t.Any) -> Date | Time | DateTime | Duration:
     return _parse(text, **options)
 
 
+def _as_datetime(value: datetime.date) -> datetime.datetime:
+    # An interval endpoint parsed from a date-only ISO 8601 value (e.g. the
+    # "2021-01-01" in "2021-01-01/P1D") is a datetime.date. Promote it to a
+    # midnight datetime so the interval has DateTime endpoints and so
+    # DateTime.add/subtract accepts the duration's time components below
+    # (Date.add/subtract does not take hours/minutes/seconds/microseconds).
+    if isinstance(value, datetime.datetime):
+        return value
+
+    return datetime.datetime(value.year, value.month, value.day)
+
+
 def _parse(
     text: str, **options: t.Any
 ) -> Date | DateTime | Time | Duration | Interval[DateTime]:
@@ -75,7 +87,9 @@ def _parse(
             duration = parsed.duration
 
             if parsed.start is not None:
-                dt = pendulum.instance(parsed.start, tz=options.get("tz", UTC))
+                dt = pendulum.instance(
+                    _as_datetime(parsed.start), tz=options.get("tz", UTC)
+                )
 
                 return pendulum.interval(
                     dt,
@@ -91,9 +105,7 @@ def _parse(
                     ),
                 )
 
-            dt = pendulum.instance(
-                t.cast("datetime.datetime", parsed.end), tz=options.get("tz", UTC)
-            )
+            dt = pendulum.instance(_as_datetime(parsed.end), tz=options.get("tz", UTC))
 
             return pendulum.interval(
                 dt.subtract(

tests/test_parsing.py

@@ -127,6 +127,24 @@ def test_parse_interval() -> None:
     assert interval.end.offset == 0
 
 
+def test_parse_interval_with_date_and_duration() -> None:
+    # The interval endpoint is a date-only value, so it parses to a
+    # datetime.date rather than a datetime.datetime. See
+    # https://github.com/python-pendulum/pendulum/issues/881
+    interval = pendulum.parse("2021-01-01/P1DT1H")
+
+    assert isinstance(interval, pendulum.Interval)
+    assert_datetime(interval.start, 2021, 1, 1, 0, 0, 0, 0)
+    assert_datetime(interval.end, 2021, 1, 2, 1, 0, 0, 0)
+
+    # The reverse form (duration then a date endpoint) goes through subtract().
+    interval = pendulum.parse("P1Y/2021-01-01")
+
+    assert isinstance(interval, pendulum.Interval)
+    assert_datetime(interval.start, 2020, 1, 1, 0, 0, 0, 0)
+    assert_datetime(interval.end, 2021, 1, 1, 0, 0, 0, 0)
+
+
 def test_parse_now() -> None:
     assert pendulum.parse("now").timezone_name == "UTC"
     assert (