cycling exclusions: supress spurious warning for exclusion points

* Closes #5659

cylc/flow/cycling/iso8601.py

@@ -269,8 +269,14 @@ def build_exclusions(self, excl_points):
         for point in excl_points:
             try:
                 # Try making an ISO8601Sequence
-                exclusion = ISO8601Sequence(point, self.exclusion_start_point,
-                                            self.exclusion_end_point)
+                exclusion = ISO8601Sequence(
+                    point,
+                    self.exclusion_start_point,
+                    self.exclusion_end_point,
+                    # disable warnings which are logged when exclusion is a
+                    # time point
+                    zero_duration_warning=False,
+                )
                 self.exclusion_sequences.append(exclusion)
             except (AttributeError, TypeError, ValueError):
                 # Try making an ISO8601Point
@@ -284,7 +290,20 @@ class ISO8601Sequence(SequenceBase):
 
     """A sequence of ISO8601 date time points separated by an interval.
     Note that an ISO8601Sequence object (may) contain
-    ISO8601ExclusionSequences"""
+    ISO8601ExclusionSequences
+
+    Args:
+        dep_section:
+            The full sequence expresion.
+        context_start_point:
+            Sequence start point from the global context.
+        context_end_point:
+            Sequence end point from the global context.
+        zero_duration_warning:
+            If `False`, then zero-duration recurrence warnings will be turned
+            off. This is set for exclusion parsing.
+
+    """
 
     TYPE = CYCLER_TYPE_ISO8601
     TYPE_SORT_KEY = CYCLER_TYPE_SORT_KEY_ISO8601
@@ -303,8 +322,13 @@ def get_async_expr(cls, start_point=None):
             return "R1"
         return "R1/" + str(start_point)
 
-    def __init__(self, dep_section, context_start_point=None,
-                 context_end_point=None):
+    def __init__(
+        self,
+        dep_section,
+        context_start_point=None,
+        context_end_point=None,
+        zero_duration_warning=True,
+    ):
         SequenceBase.__init__(
             self, dep_section, context_start_point, context_end_point)
         self.dep_section = dep_section
@@ -344,7 +368,9 @@ def __init__(self, dep_section, context_start_point=None,
         # Parse_recurrence returns an isodatetime TimeRecurrence object
         # and a list of exclusion strings.
         self.recurrence, excl_points = self.abbrev_util.parse_recurrence(
-            dep_section)
+            dep_section,
+            zero_duration_warning=zero_duration_warning,
+        )
 
         # Determine the exclusion start point and end point
         try:

cylc/flow/time_parser.py

@@ -206,9 +206,23 @@ def parse_recurrence(
         self,
         expression: str,
         context_start_point: Optional['TimePoint'] = None,
-        context_end_point: Optional['TimePoint'] = None
+        context_end_point: Optional['TimePoint'] = None,
+        zero_duration_warning: bool = True,
     ) -> Tuple[TimeRecurrence, list]:
-        """Parse an expression in abbrev. or full ISO recurrence format."""
+        """Parse an expression in abbrev. or full ISO recurrence format.
+
+        Args:
+            expression:
+                The recurrence expression to parse.
+            context_start_point:
+                Sequence start point from the global context.
+            context_end_point:
+                Sequence end point from the global context.
+            zero_duration_warning:
+                If `False`, then zero-duration recurrence warnings will be
+                turned off. This is set for exclusion parsing.
+
+        """
         expression, exclusions = parse_exclusion(str(expression))
 
         if context_start_point is None:
@@ -301,8 +315,11 @@ def parse_recurrence(
                     repetitions += 1
                 end_point = None
 
-            if not interval and repetitions != 1 and (
-                (format_num != 1 or start_point == end_point)
+            if (
+                zero_duration_warning
+                and not interval
+                and repetitions != 1
+                and (format_num != 1 or start_point == end_point)
             ):
                 LOG.warning(
                     "Cannot have more than 1 repetition for zero-duration "

tests/unit/cycling/test_iso8601.py

@@ -584,6 +584,29 @@ def test_multiple_exclusions_extensive(set_cycling_type):
     assert sequence.get_prev_point(point_4) == point_1
 
 
+def test_exclusion_zero_duration_warning(set_cycling_type, caplog, log_filter):
+    """It should not log zero-duration warnings for exclusion points.
+
+    Exclusions may either be sequences or points. We first attempt to parse
+    them as sequences, if this fails, we attempt to parse them as points.
+
+    The zero-duration recurrence warning would be logged if we attempted to
+    parse a point as a sequence. To avoid spurious warnings this should be
+    turned off for exclusion parsing.
+
+    """
+    # parsing a point as a sequences causes a zero-duration warning
+    set_cycling_type(ISO8601_CYCLING_TYPE, "+05")
+    with pytest.raises(Exception):
+        ISO8601Sequence('3000', '2999')
+    assert log_filter(caplog, contains='zero-duration')
+
+    # parsing a point in an exclusion should not
+    caplog.clear()
+    ISO8601Sequence('P1Y ! 3000', '2999')
+    assert not log_filter(caplog, contains='zero-duration')
+
+
 def test_simple(set_cycling_type):
     """Run some simple tests for date-time cycling."""
     set_cycling_type(ISO8601_CYCLING_TYPE, "Z")