Issue a warning when a parameter is not consumed by a task (#3170)

luigi/parameter.py

@@ -95,6 +95,10 @@ class OptionalParameterTypeWarning(UserWarning):
     pass
 
 
+class UnconsumedParameterWarning(UserWarning):
+    """Warning class for parameters that are not consumed by the task."""
+
+
 class Parameter:
     """
     Parameter whose value is a ``str``, and a base class for other parameter types.

luigi/task.py

@@ -32,9 +32,11 @@
 
 import luigi
 
+from luigi import configuration
 from luigi import parameter
 from luigi.task_register import Register
 from luigi.parameter import ParameterVisibility
+from luigi.parameter import UnconsumedParameterWarning
 
 Parameter = parameter.Parameter
 logger = logging.getLogger('luigi-interface')
@@ -429,6 +431,23 @@ def list_to_tuple(x):
                 return tuple(x)
             else:
                 return x
+
+        # Check for unconsumed parameters
+        conf = configuration.get_config()
+        if not hasattr(cls, "_unconsumed_params"):
+            cls._unconsumed_params = set()
+        if task_family in conf.sections():
+            for key, value in conf[task_family].items():
+                composite_key = f"{task_family}_{key}"
+                if key not in result and composite_key not in cls._unconsumed_params:
+                    warnings.warn(
+                        "The configuration contains the parameter "
+                        f"'{key}' with value '{value}' that is not consumed by the task "
+                        f"'{task_family}'.",
+                        UnconsumedParameterWarning,
+                    )
+                    cls._unconsumed_params.add(composite_key)
+
         # Sort it by the correct order and make a list
         return [(param_name, list_to_tuple(result[param_name])) for param_name, param_obj in params]
 

test/task_test.py

@@ -169,6 +169,55 @@ class ATaskWithBadParam(luigi.Task):
         with self.assertRaisesRegex(ValueError, r"ATaskWithBadParam\[args=\(\), kwargs={}\]: Error when parsing the default value of 'bad_param'"):
             ATaskWithBadParam()
 
+    @with_config(
+        {
+            "TaskA": {
+                "a": "a",
+                "b": "b",
+                "c": "c",
+            },
+            "TaskB": {
+                "a": "a",
+                "b": "b",
+                "c": "c",
+            },
+        }
+    )
+    def test_unconsumed_params(self):
+        class TaskA(luigi.Task):
+            a = luigi.Parameter(default="a")
+
+        class TaskB(luigi.Task):
+            a = luigi.Parameter(default="a")
+
+        with warnings.catch_warnings(record=True) as w:
+            warnings.filterwarnings(
+                action="ignore",
+                category=Warning,
+            )
+            warnings.simplefilter(
+                action="always",
+                category=luigi.parameter.UnconsumedParameterWarning,
+            )
+
+            TaskA()
+            TaskB()
+
+            assert len(w) == 4
+            expected = [
+                ("b", "TaskA"),
+                ("c", "TaskA"),
+                ("b", "TaskB"),
+                ("c", "TaskB"),
+            ]
+            for i, (expected_value, task_name) in zip(w, expected):
+                assert issubclass(i.category, luigi.parameter.UnconsumedParameterWarning)
+                assert str(i.message) == (
+                    "The configuration contains the parameter "
+                    f"'{expected_value}' with value '{expected_value}' that is not consumed by "
+                    f"the task '{task_name}'."
+                )
+
 
 class ExternalizeTaskTest(LuigiTestCase):