Use previous parameter merge strategy

We don't allow different parameter merge strategies
in different environment files for a parameter. If
a merge strategy has already been provided in one
environment file, let's use that for subsequent ones
unless a different merge strategy has been provided.

Task: 45578
Change-Id: Iec3367667248d0b46196a6d569f3cbb3b200d842
(cherry picked from commit 94f32ee39f4d705614079bd0ac113cde67dbb7e4)
(cherry picked from commit f0507980586711014e28411d53faba30138c3044)
(cherry picked from commit 66dd43c6555451e4a6f60d82ef8da33cc83f6397)

1 files changed, 8 insertions, 3 deletions

diff --git a/heat/common/environment_util.py b/heat/common/environment_util.py
index 8a6ed4393..5143719d8 100644
--- a/heat/common/environment_util.py
+++ b/heat/common/environment_util.py
@@ -22,14 +22,19 @@ ALLOWED_PARAM_MERGE_STRATEGIES = (OVERWRITE, MERGE, DEEP_MERGE) = (
     'overwrite', 'merge', 'deep_merge')
 
 
-def get_param_merge_strategy(merge_strategies, param_key):
+def get_param_merge_strategy(merge_strategies, param_key,
+                             available_strategies=None):
+    if not available_strategies:
+        available_strategies = {}
 
     if merge_strategies is None:
         return OVERWRITE
 
     env_default = merge_strategies.get('default', OVERWRITE)
+    merge_strategy = merge_strategies.get(
+        param_key, available_strategies.get(
+            param_key, env_default))
 
-    merge_strategy = merge_strategies.get(param_key, env_default)
     if merge_strategy in ALLOWED_PARAM_MERGE_STRATEGIES:
         return merge_strategy
 
@@ -114,7 +119,7 @@ def merge_parameters(old, new, param_schemata, strategies_in_file,
         # if key not in param_schemata ignore it
         if key in param_schemata and value is not None:
             param_merge_strategy = get_param_merge_strategy(
-                strategies_in_file, key)
+                strategies_in_file, key, available_strategies)
             if key not in available_strategies:
                 new_strategies[key] = param_merge_strategy