Better queue config warning.

CHANGES.md

@@ -61,6 +61,9 @@ files are now auto-documented from their definitions.
 
 ### Fixes
 
+[#3618](https://github.com/cylc/cylc-flow/pull/3618) - Clear queue configuration
+warnings for referencing undefined or unused tasks.
+
 [#3596](https://github.com/cylc/cylc-flow/pull/3596) - Fix a bug that could
 prevent housekeeping of the task_action_timers DB table and cause many warnings
 at restart.

cylc/flow/config.py

@@ -1138,8 +1138,12 @@ def configure_queues(self):
                                     'already assigned to a queue')
                                 warnings.append(msg)
                             elif qmember not in all_task_names:
+                                if qmember not in self.cfg['runtime']:
+                                    err = 'task not defined'
+                                else:
+                                    err = 'task not used in the graph'
                                 msg = "%s: ignoring %s (%s)" % (
-                                    key, qmember, 'task not defined')
+                                    key, qmember, err)
                                 warnings.append(msg)
                             else:
                                 # Ignore: task not used in the graph.

cylc/flow/tests/test_config.py

@@ -213,7 +213,8 @@ def test_family_inheritance_and_quotes(self):
                        config.runtime['descendants']['SOMEFAM']
 
 
-def test_queue_config(caplog, tmp_path):
+def test_queue_config_repeated(caplog, tmp_path):
+    """Test repeated assignment to same queue."""
     suiterc_content = """
 [scheduling]
    [[queues]]
@@ -236,3 +237,30 @@ def test_queue_config(caplog, tmp_path):
     log = caplog.messages[0].split('\n')
     assert log[0] == "Queue configuration warnings:"
     assert log[1] == "+ q2: ignoring x (already assigned to a queue)"
+
+
+def test_queue_config_not_used_not_defined(caplog, tmp_path):
+    """Test task not defined vs no used, in queue config."""
+    suiterc_content = """
+[scheduling]
+   [[queues]]
+       [[[q1]]]
+           members = foo
+       [[[q2]]]
+           members = bar
+   [[dependencies]]
+       # foo and bar not used
+       graph = "beef => wellington"
+[runtime]
+   [[beef]]
+   [[wellington]]
+   [[foo]]
+   # bar not even defined
+    """
+    suite_rc = tmp_path / "suite.rc"
+    suite_rc.write_text(suiterc_content)
+    config = SuiteConfig(suite="qtest", fpath=suite_rc.absolute())
+    log = caplog.messages[0].split('\n')
+    assert log[0] == "Queue configuration warnings:"
+    assert log[1] == "+ q1: ignoring foo (task not used in the graph)"
+    assert log[2] == "+ q2: ignoring bar (task not defined)"