Allow setting of default batch system directives in the platform config

cylc/flow/cfgspec/globalcfg.py

@@ -1308,6 +1308,17 @@
                       be appropriate if following the pattern
                       ``hosts = main, backup, failsafe``.
                 ''')
+            with Conf('directives', desc='''
+                Job runner (batch scheduler) directives.
+
+                Default directives for :cylc:conf:
+                `[runtime][<namespace>][directives]`
+            '''):
+                Conf('<directive>', VDR.V_STRING, desc='''
+                    Example directives for the built-in job runner handlers
+                    are shown in :ref:`AvailableMethods`.
+                ''')
+
         with Conf('localhost', meta=Platform, desc='''
             A default platform defining settings for jobs to be run on the
             same host as the workflow scheduler.

cylc/flow/task_job_mgr.py

@@ -1278,6 +1278,27 @@ def _prep_submit_task_job_impl(self, workflow, itask, rtconfig):
             job_d=job_d
         )
 
+    @staticmethod
+    def default_dict_merger(defaults, tdef):
+        """Use directive from platform if not set in rtconfig.
+
+        For item in defaults add item to output if not in tdef.
+
+        Examples:
+        >>> defaults = {'use': 1, 'override': 1}
+        >>> tdef = {'override': 2, 'nodefault': 1}
+        >>> result = TaskJobManager.default_dict_merger(defaults, tdef)
+        >>> {i: result[i] for i in sorted(result)}
+        {'nodefault': 1, 'override': 2, 'use': 1}
+        """
+        output = {}
+        for key in set(list(defaults.keys()) + list(tdef.keys())):
+            if key in defaults and key not in tdef:
+                output[key] = defaults[key]
+            else:
+                output[key] = tdef[key]
+        return output
+
     def get_job_conf(
         self,
         workflow,
@@ -1299,7 +1320,9 @@ def get_job_conf(
                 itask.platform['job runner command template']
             ),
             'dependencies': itask.state.get_resolved_dependencies(),
-            'directives': rtconfig['directives'],
+            'directives': self.default_dict_merger(
+                itask.platform['directives'], rtconfig['directives']
+            ),
             'environment': rtconfig['environment'],
             'execution_time_limit': itask.summary[self.KEY_EXECUTE_TIME_LIMIT],
             'env-script': rtconfig['env-script'],

tests/functional/platforms/09-default-directives.t

@@ -0,0 +1,70 @@
+#!/usr/bin/env bash
+# THIS FILE IS PART OF THE CYLC WORKFLOW ENGINE.
+# Copyright (C) NIWA & British Crown (Met Office) & Contributors.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#-------------------------------------------------------------------------------
+# Test validating platforms in workflow.
+REQUIRE_PLATFORM="runner:slurm"
+. "$(dirname "$0")/test_header"
+
+set_test_number 5
+
+create_test_global_config "" "
+    [platforms]
+        [[no_default, default_only, overridden, neither]]
+            hosts = localhost
+            job runner = slurm
+        [[default_only, overridden]]
+            [[[directives]]]
+                --wurble=foo
+"
+
+init_workflow "${TEST_NAME_BASE}" <<'__FLOW_CONF__'
+[scheduler]
+    [[events]]
+        stall timeout = PT0S
+[scheduling]
+    [[graph]]
+        R1 = lewis & morse & barnaby & cadfael
+
+[runtime]
+    [[lewis]]
+        platform = no_default
+        [[[directives]]]
+            --wurble=bar
+    [[morse]]
+        platform = default_only
+    [[barnaby]]
+        platform = overridden
+        [[[directives]]]
+            --wurble=qux
+    [[cadfael]]
+        platform = neither
+
+__FLOW_CONF__
+
+run_fail "${TEST_NAME_BASE}-play" \
+    cylc play ${WORKFLOW_NAME} --no-detach
+
+LOG_DIR="${RUN_DIR}/${WORKFLOW_NAME}/log/job/1/"
+
+named_grep_ok "${TEST_NAME_BASE}-no-default" "--wurble=bar" "${LOG_DIR}/lewis/NN/job"
+named_grep_ok "${TEST_NAME_BASE}-default-only" "--wurble=foo" "${LOG_DIR}/morse/NN/job"
+named_grep_ok "${TEST_NAME_BASE}-overridden" "--wurble=qux" "${LOG_DIR}/barnaby/NN/job"
+grep_fail "--wurble" "${LOG_DIR}/cadfael/NN/job"
+
+purge
+exit 0
+