Make trigger and set warnings consistent again.

Author: hjoliver

cylc/flow/task_pool.py

@@ -2045,13 +2045,14 @@ def set_prereqs_and_outputs(
             return
 
         # For active tasks, default to the task's current flow assignment.
+        warnings_flow_none = []
         if itasks:
             flow_nums = self.get_flow_nums(flow, flow_descr)
             for itask in itasks:
                 if flow == ['none'] and itask.flow_nums != set():
-                    LOG.error(
-                        f"[{itask}] ignoring 'flow=none' set: task already has"
-                        f" {repr_flow_nums(itask.flow_nums, full=True)}"
+                    warnings_flow_none.append(
+                        f"{itask.identity}: "
+                        f"{repr_flow_nums(itask.flow_nums, full=True)}"
                     )
                     continue
 
@@ -2076,6 +2077,13 @@ def set_prereqs_and_outputs(
                     self._set_outputs_itask(itask, outputs)
                     no_op = False
 
+        if warnings_flow_none:
+            msg = '\n  * '.join(warnings_flow_none)
+            LOG.warning(
+                "Tasks already flow-assigned - ignoring "
+                f'"trigger --flow=none": \n  * {msg}'
+            )
+
         # For inactive tasks, default to all current flows.
         if inactive_tasks:
             flow_nums = self.get_flow_nums(flow or [FLOW_ALL], flow_descr)

tests/integration/test_flow_assignment.py

@@ -27,7 +27,6 @@
     FLOW_ALL,
     FLOW_NEW,
     FLOW_NONE,
-    repr_flow_nums
 )
 from cylc.flow.scheduler import Scheduler
 
@@ -137,11 +136,8 @@ async def test_flow_assignment(
         do_command([active_a.identity], flow=[FLOW_NONE])
         assert active_a.flow_nums == {1, 2}
         assert log_filter(
-            contains=(
-                f'[{active_a}] ignoring \'flow=none\' {command}: '
-                f'task already has {repr_flow_nums(active_a.flow_nums)}'
-            ),
-            level=logging.ERROR
+            contains=("Tasks already flow-assigned - ignoring"),
+            level=logging.WARNING
         )
 
         do_command([active_a.identity], flow=[FLOW_NEW])