Adding 'json_pp' function in YAQL

* Added new function called 'json_pp'
   for pretty output json objects using YAQL.
   It can be used, for example, for sending email
   containing some dicts or lists.
 * This function also fixes escaped new-line symbols

Change-Id: I8a7d432a957423b832935f46bb04ddd4505258c7

mistral/tests/unit/test_expressions.py

@@ -111,6 +111,24 @@ class YaqlEvaluatorTest(base.BaseTest):
                           self._evaluator.validate,
                           {'a': 1})
 
+    def test_json_pp(self):
+        self.assertEqual('"3"', self._evaluator.evaluate('json_pp($)', '3'))
+        self.assertEqual('3', self._evaluator.evaluate('json_pp($)', 3))
+        self.assertEqual(
+            '[\n    1, \n    2\n]',
+            self._evaluator.evaluate('json_pp($)', [1, 2])
+        )
+        self.assertEqual(
+            '{\n    "a": "b"\n}',
+            self._evaluator.evaluate('json_pp($)', {'a': 'b'})
+        )
+        self.assertEqual(
+            '"Mistral\nis\nawesome"',
+            self._evaluator.evaluate(
+                'json_pp($)', '\n'.join(['Mistral', 'is', 'awesome'])
+            )
+        )
+
 
 class InlineYAQLEvaluatorTest(base.BaseTest):
     def setUp(self):

mistral/utils/yaql_utils.py

@@ -12,6 +12,8 @@
 #    See the License for the specific language governing permissions and
 #    limitations under the License.
 
+import json
+
 import yaql
 
 from mistral.db.v2 import api as db_api
@@ -42,6 +44,7 @@ def _register_functions(yaql_ctx):
     yaql_ctx.register_function(env_)
     yaql_ctx.register_function(execution_)
     yaql_ctx.register_function(task_)
+    yaql_ctx.register_function(json_pp_, name='json_pp')
 
 
 # Additional YAQL functions needed by Mistral.
@@ -56,6 +59,10 @@ def execution_(context):
     return context['__execution']
 
 
+def json_pp_(data):
+    return json.dumps(data, indent=4).replace("\\n", "\n")
+
+
 def task_(context, task_name):
     # Importing data_flow in order to break cycle dependency between modules.
     from mistral.workflow import data_flow