Add extrinsic to merge array of objects into one.

cfpp/extrinsics.py

@@ -199,6 +199,15 @@ def kms__encrypt_file(config, context, args):
     return base64.b64encode(ciphertext["CiphertextBlob"])
 
 
+@extrinsic
+def merge(config, context, args):
+    _raise_unless_array_of_dictionaries(context, args)
+    result = {}
+    for arg in args:
+        result.update(arg)
+    return result
+
+
 class ContextException(Exception):
     def __init__(self, context, message):
         message = "%s: %s" % (".".join(context), message)
@@ -243,6 +252,14 @@ def _raise_unless_array_of_strings(context, arg):
             raise UnexpectedArgumentTypeException(context, unicode, element)
 
 
+def _raise_unless_array_of_dictionaries(context, arg):
+    if not isinstance(arg, list):
+        raise UnexpectedArgumentTypeException(context, list, arg)
+    for element in arg:
+        if not isinstance(element, dict):
+            raise UnexpectedArgumentTypeException(context, dict, element)
+
+
 def _raise_unless_include_args(context, arg):
     if not isinstance(arg, list):
         raise UnexpectedArgumentTypeException(context, list, arg)

tests/0005_merge.output.json

@@ -0,0 +1,15 @@
+{
+  "AWSTemplateFormatVersion": "2010-09-09",
+  "Description": "",
+  "Resources": {
+    "FirstResource": {
+      "Tag": "FirstTag"
+    },
+    "SecondResource": {
+      "Tag": "SecondTag"
+    },
+    "OverriddenResource": {
+      "Tag": "OverriddenTag"
+    }
+  }
+}

tests/0005_merge.template

@@ -0,0 +1,19 @@
+{
+  "AWSTemplateFormatVersion": "2010-09-09",
+  "Description": "",
+  "Resources": {
+    "CFPP::Merge": [
+      {
+        "CFPP::JsonFile": "0005_resource_snippet.json"
+      },
+      {
+        "SecondResource": {
+          "Tag": "SecondTag"
+        },
+        "OverriddenResource": {
+          "Tag": "OverriddenTag"
+        }
+      }
+    ]
+  }
+}

tests/0005_resource_snippet.json

@@ -0,0 +1,8 @@
+{
+  "FirstResource": {
+    "Tag": "FirstTag"
+  },
+  "OverriddenResource": {
+    "Tag": "OriginalTag"
+  }
+}