Ensure that platform from group selection checks broadcast manager

for updates to task config.
Ensure that 255 callback gives a sensible platform in warning messages.

changes.d/6330.fix.md

@@ -0,0 +1 @@
+Fix bug where broadcasting failed to change platform selected after host selection failure.

cylc/flow/task_job_mgr.py

@@ -306,10 +306,12 @@ def submit_task_jobs(self, workflow, itasks, curve_auth,
 
  # Get another platform, if task config platform is a group
  use_next_platform_in_group = False
- if itask.tdef.rtconfig['platform']:
+ bc_mgr = self.task_events_mgr.broadcast_mgr
+ rtconf = bc_mgr.get_updated_rtconfig(itask)
+ if rtconf['platform']:
  try:
  platform = get_platform(
- itask.tdef.rtconfig['platform'],
+ rtconf['platform'],
  bad_hosts=self.bad_hosts
  )
  except PlatformLookupError:

tests/integration/test_task_job_mgr.py

@@ -187,3 +187,52 @@ async def test__prep_submit_task_job_impl_handles_execution_time_limit(
  schd.task_job_mgr._prep_submit_task_job(
  schd.workflow, task_a)
  assert not task_a.summary.get('execution_time_limit', '')
+
+
+async def test_broadcast_platform_change(
+ mock_glbl_cfg,
+ flow,
+ scheduler,
+ start,
+ log_filter,
+):
+ """Broadcast can change task platform.
+
+ Even after host selection failure.
+
+ see https://github.com/cylc/cylc-flow/issues/6320
+ """
+ mock_glbl_cfg(
+ 'cylc.flow.platforms.glbl_cfg',
+ '''
+ [platforms]
+ [[foo]]
+ hosts = food
+ ''')
+
+ id_ = flow({
+ "scheduling": {"graph": {"R1": "mytask"}},
+ # Platform = None doesn't cause this issue!
+ "runtime": {"mytask": {"platform": "localhost"}}})
+
+ schd = scheduler(id_, run_mode='live')
+
+ async with start(schd) as log:
+ # Change the task platform with broadcast:
+ schd.broadcast_mgr.put_broadcast(
+ ['1'], ['mytask'], [{'platform': 'foo'}])
+
+ # Simulate prior failure to contact hosts:
+ schd.task_job_mgr.task_remote_mgr.bad_hosts = {'food'}
+
+ # Attempt job submission:
+ schd.task_job_mgr.submit_task_jobs(
+ schd.workflow,
+ schd.pool.get_tasks(),
+ schd.server.curve_auth,
+ schd.server.client_pub_key_dir)
+
+ # Check that task platform hasn't become "localhost":
+ assert schd.pool.get_tasks()[0].platform['name'] == 'foo'
+ # ... and that remote init failed because all hosts bad:
+ assert log_filter(log, contains="(no hosts were reachable)")