New feature: add new meta action `end_play`

This feature also cleans up and extends the meta subsystem:
* Allows for some meta actions (noop, clear_facts, clear_host_errors,
  and end_play) to operate on a per-host basis, meaning they can work
  with the free strategy as expected.
* Allows for conditionals on meta tasks.
* Fixes a bug where (for the linear strategy) metas were not treated
  as a run_once task, meaning every host in inventory would run the
  meta task.

Fixes #1476

lib/ansible/plugins/strategy/__init__.py

@@ -695,28 +695,63 @@ class StrategyBase:
 
         return ret
 
-    def _execute_meta(self, task, play_context, iterator):
+    def _execute_meta(self, task, play_context, iterator, target_host=None):
 
         # meta tasks store their args in the _raw_params field of args,
         # since they do not use k=v pairs, so get that
         meta_action = task.args.get('_raw_params')
 
+        # FIXME(s):
+        # * raise an error or show a warning when a conditional is used
+        #   on a meta task that doesn't support them
+
+        def _evaluate_conditional(h):
+            all_vars = self._variable_manager.get_vars(loader=self._loader, play=iterator._play, host=host, task=task)
+            templar = Templar(loader=self._loader, variables=all_vars)
+            return task.evaluate_conditional(templar, all_vars)
+
+        if target_host:
+            host_list = [target_host]
+        else:
+            host_list = [host for host in self._inventory.get_hosts(iterator._play.hosts) if host.name not in self._tqm._unreachable_hosts]
+
+        results = []
+        for host in host_list:
+            result = None
             if meta_action == 'noop':
                 # FIXME: issue a callback for the noop here?
-            pass
+                result = TaskResult(host, task, dict(changed=False, msg="noop"))
             elif meta_action == 'flush_handlers':
                 self.run_handlers(iterator, play_context)
             elif meta_action == 'refresh_inventory':
                 self._inventory.refresh_inventory()
+                result = TaskResult(host, task, dict(changed=False, msg="inventory successfully refreshed"))
             elif meta_action == 'clear_facts':
-            for host in iterator._host_states:
+                if _evaluate_conditional(host):
-                self._variable_manager.clear_facts(host)
+                    self._variable_manager.clear_facts(target_host)
+                    result = TaskResult(host, task, dict(changed=True, msg="inventory successfully refreshed"))
+                else:
+                    result = TaskResult(host, task, dict(changed=False, skipped=True))
+            elif meta_action == 'clear_host_errors':
+                if _evaluate_conditional(host):
+                    self._tqm._failed_hosts.pop(host.name, False)
+                    self._tqm._unreachable_hosts.pop(host.name, False)
+                    iterator._host_states[host.name].fail_state = iterator.FAILED_NONE
+                    result = TaskResult(host, task, dict(changed=True, msg="successfully cleared host errors"))
+                else:
+                    result = TaskResult(host, task, dict(changed=False, skipped=True))
+            elif meta_action == 'end_play':
+                if _evaluate_conditional(host):
+                    iterator._host_states[host.name].run_state = iterator.ITERATING_COMPLETE
+                    result = TaskResult(host, task, dict(changed=True, msg="ending play"))
+                else:
+                    result = TaskResult(host, task, dict(changed=False, skipped=True))
             #elif meta_action == 'reset_connection':
             #    connection_info.connection.close()
-        elif meta_action == 'clear_host_errors':
-            self._tqm._failed_hosts = dict()
-            self._tqm._unreachable_hosts = dict()
-            for host in iterator._host_states:
-                iterator._host_states[host].fail_state = iterator.FAILED_NONE
             else:
                 raise AnsibleError("invalid meta action requested: %s" % meta_action, obj=task._ds)
+
+            if result is not None:
+                results.append(result)
+
+        return results

lib/ansible/plugins/strategy/free.py

@@ -137,7 +137,7 @@ class StrategyModule(StrategyBase):
                                 continue
 
                         if task.action == 'meta':
-                            self._execute_meta(task, play_context, iterator)
+                            self._execute_meta(task, play_context, iterator, target_host=host)
                             self._blocked_hosts[host_name] = False
                         else:
                             # handle step if needed, skip meta actions as they are used internally

lib/ansible/plugins/strategy/linear.py

@@ -214,7 +214,10 @@ class StrategyModule(StrategyBase):
                             continue
 
                     if task.action == 'meta':
-                        self._execute_meta(task, play_context, iterator)
+                        # for the linear strategy, we run meta tasks just once and for
+                        # all hosts currently being iterated over rather than one host
+                        results.extend(self._execute_meta(task, play_context, iterator))
+                        run_once = True
                     else:
                         # handle step if needed, skip meta actions as they are used internally
                         if self._step and choose_step: