Fixing YAQL related errors

* Now Mistral raises YaqlEvaluationException if
   something was wrong with evaluating YAQL.

Closes-Bug: #1449505

Change-Id: Ic6a1592b8424ebdbaaca698b9a894d589def97d2

mistral/expressions.py

@@ -89,7 +89,7 @@ class YAQLEvaluator(Evaluator):
                 data=data_context,
                 context=yaql_utils.create_yaql_context()
             )
-        except (KeyError, yaql_exc.YaqlException) as e:
+        except (yaql_exc.YaqlException, KeyError, ValueError, TypeError) as e:
             raise exc.YaqlEvaluationException(
                 "Can not evaluate YAQL expression: %s, data = %s; error:"
                 " %s" % (expression, data_context, str(e))

mistral/tests/unit/engine/test_direct_workflow.py

@@ -262,6 +262,27 @@ class DirectWorkflowEngineTest(base.EngineTestCase):
                 "Called with a right exception"
             )
 
+    def test_mismatched_yaql_in_first_task(self):
+        wf_text = """
+        version: '2.0'
+
+        wf:
+          input:
+            - var
+          tasks:
+            task1:
+              action: std.echo output=<% $.var + $.var2 %>
+        """
+
+        wf_service.create_workflows(wf_text)
+
+        exception = self.assertRaises(
+            exc.YaqlEvaluationException,
+            self.engine.start_workflow, 'wf', {'var': 2}
+        )
+
+        self.assertIn("Can not evaluate YAQL expression", exception.message)
+
     def test_one_line_syntax_in_on_clauses(self):
         wf_text = """
         version: '2.0'