Update based on review comments

airflow/models/dag.py

@@ -119,7 +119,7 @@
 from airflow.utils.dag_cycle_tester import check_cycle
 from airflow.utils.dates import cron_presets, date_range as utils_date_range
 from airflow.utils.decorators import fixup_decorator_warning_stack
-from airflow.utils.helpers import at_least_one, at_most_one, exactly_one, validate_key
+from airflow.utils.helpers import at_most_one, exactly_one, validate_key
 from airflow.utils.log.logging_mixin import LoggingMixin
 from airflow.utils.session import NEW_SESSION, provide_session
 from airflow.utils.sqlalchemy import (
@@ -549,7 +549,10 @@ def __init__(
         # sort out DAG's scheduling behavior
         scheduling_args = [schedule_interval, timetable, schedule]
 
-        if at_least_one(*scheduling_args) and not ("start_date" in self.default_args or self.start_date):
+        has_scheduling_args = any(a is not NOTSET and bool(a) for a in scheduling_args)
+        has_empty_start_date = not ("start_date" in self.default_args or self.start_date)
+
+        if has_scheduling_args and has_empty_start_date:
             raise ValueError("DAG is missing the start_date parameter")
 
         if not at_most_one(*scheduling_args):

airflow/utils/helpers.py

@@ -325,24 +325,6 @@ def is_set(val):
     return sum(map(is_set, args)) in (0, 1)
 
 
-def at_least_one(*args) -> bool:
-    """
-    Return True if at least one of *args is "truthy", and False otherwise.
-
-    NOTSET is treated the same as None.
-
-    If user supplies an iterable, we raise ValueError and force them to unpack.
-    """
-
-    def is_set(val):
-        if val is NOTSET:
-            return False
-        else:
-            return bool(val)
-
-    return sum(map(is_set, args)) > 0
-
-
 def prune_dict(val: Any, mode="strict"):
     """
     Given dict ``val``, returns new dict based on ``val`` with all empty elements removed.

tests/utils/test_helpers.py

@@ -27,7 +27,6 @@
 from airflow.jobs.base_job_runner import BaseJobRunner
 from airflow.utils import helpers, timezone
 from airflow.utils.helpers import (
-    at_least_one,
     at_most_one,
     build_airflow_url_with_query,
     exactly_one,
@@ -304,34 +303,6 @@ def assert_at_most_one(true=0, truthy=0, false=0, falsy=0, notset=0):
             print(row)
             assert_at_most_one(*row)
 
-    def test_at_least_one(self):
-        """
-        Checks that when we set ``true_count`` elements to "truthy", and others to "falsy",
-        we get the expected return.
-        We check for both True / False, and truthy / falsy values 'a' and '', and verify that
-        they can safely be used in any combination.
-        NOTSET values should be ignored.
-        """
-
-        def assert_at_least_one(true=0, truthy=0, false=0, falsy=0, notset=0):
-            sample = []
-            for truth_value, num in [
-                (True, true),
-                (False, false),
-                ("a", truthy),
-                ("", falsy),
-                (NOTSET, notset),
-            ]:
-                if num:
-                    sample.extend([truth_value] * num)
-            if sample:
-                expected = True if true + truthy > 0 else False
-                assert at_least_one(*sample) is expected
-
-        for row in itertools.product(range(4), repeat=4):
-            print(row)
-            assert_at_least_one(*row)
-
     @pytest.mark.parametrize(
         "mode, expected",
         [