Add new environment section for merge strategies

This adds a new evironment section 'parameter_merge_strategies'.
These strategies would subsequently be used to merge parameters
and parameter_defaults from environment files.

Change-Id: Ib2b84ecdb2a1516ea0c5ced25a1fed408b954694
Blueprint: environment-merging

heat/common/environment_format.py

@@ -17,10 +17,12 @@ from heat.common import template_format
 
 SECTIONS = (
     PARAMETERS, RESOURCE_REGISTRY, PARAMETER_DEFAULTS,
-    ENCRYPTED_PARAM_NAMES, EVENT_SINKS
+    ENCRYPTED_PARAM_NAMES, EVENT_SINKS,
+    PARAMETER_MERGE_STRATEGIES,
 ) = (
     'parameters', 'resource_registry', 'parameter_defaults',
-    'encrypted_param_names', 'event_sinks'
+    'encrypted_param_names', 'event_sinks',
+    'parameter_merge_strategies',
 )
 
 
@@ -63,7 +65,7 @@ def validate(env):
 def default_for_missing(env):
     """Checks a parsed environment for missing sections."""
     for param in SECTIONS:
-        if param not in env:
+        if param not in env and param != PARAMETER_MERGE_STRATEGIES:
             if param in (ENCRYPTED_PARAM_NAMES, EVENT_SINKS):
                 env[param] = []
             else:

heat/tests/test_environment_format.py

@@ -34,6 +34,21 @@ resource_registry: {}
         tpl2 = environment_format.parse(yaml2)
         self.assertEqual(tpl1, tpl2)
 
+    def test_param_valid_strategy_section(self):
+        yaml1 = ''
+        yaml2 = '''
+parameters: {}
+encrypted_param_names: []
+parameter_defaults: {}
+parameter_merge_strategies: {}
+event_sinks: []
+resource_registry: {}
+'''
+        tpl1 = environment_format.parse(yaml1)
+        environment_format.default_for_missing(tpl1)
+        tpl2 = environment_format.parse(yaml2)
+        self.assertNotEqual(tpl1, tpl2)
+
     def test_wrong_sections(self):
         env = '''
 parameters: {}