Check that template format plugins are registered

Otherwise log an error and exit

Change-Id: I2beb33371cf5e6701e22dbb41c8f5aa681c379de
Closes-Bug: #1402426
(cherry picked from commit ed76af4)

bin/heat-engine

@@ -35,7 +35,9 @@ if os.path.exists(os.path.join(POSSIBLE_TOPDIR, 'heat', '__init__.py')):
 from oslo.config import cfg
 from oslo import i18n
 
+from heat.common.i18n import _LC
 from heat.common import messaging
+from heat.engine import template
 from heat.openstack.common import log as logging
 from heat.openstack.common import service
 
@@ -51,6 +53,14 @@ if __name__ == '__main__':
     logging.setup('heat')
     messaging.setup()
 
+    mgr = None
+    try:
+        mgr = template._get_template_extension_manager()
+    except template.TemplatePluginNotRegistered as ex:
+        LOG.critical(_LC("%s"), ex)
+    if not mgr or not mgr.names():
+        sys.exit("ERROR: No template format plugins registered")
+
     from heat.engine import service as engine
 
     srv = engine.EngineService(cfg.CONF.host, rpc_api.ENGINE_TOPIC)

heat/engine/template.py

@@ -52,7 +52,16 @@ def _get_template_extension_manager():
     return extension.ExtensionManager(
         namespace='heat.templates',
         invoke_on_load=False,
-        verify_requirements=True)
+        verify_requirements=True,
+        on_load_failure_callback=raise_extension_exception)
+
+
+def raise_extension_exception(extmanager, ep, err):
+    raise TemplatePluginNotRegistered(name=ep.name, error=six.text_type(err))
+
+
+class TemplatePluginNotRegistered(exception.HeatException):
+    msg_fmt = _("Could not load %(name)s: %(error)s")
 
 
 def get_template_class(template_data):