pyyaml 4.1 raised an error during testing of parsing of 'yaml'-format…

… templates

Our output documents support a 'yaml' experimental template format. In this format, we recursively walk the data structure and replace string values by evaluating them as their own output document templates. However, when we run documents in the PARSE_ONLY mode for validating modules, the inner document templates return junk values if validation passes, and if these junk values are not safe for YAML output (i.e. not basic data types), pyyaml 4.1 raises an exception.

The fix is to not render the substituted data structure back to YAML when the caller is just testing that e.g. Jinja2 syntax is correct.

guidedmodules/module_logic.py

@@ -430,6 +430,14 @@ def walk(value, path):
         # Render strings within the data structure.
         value = walk(template_body, [])
 
+        # If we're just testing parsing the template, return
+        # any output now. Since the inner templates may have
+        # returned a value of any type, we can't serialize back to
+        # JSON --- pyyaml's safe dumper will raise an error if
+        # it gets a non-safe value type.
+        if output_format == "PARSE_ONLY":
+            return value
+
         # Render to JSON or YAML depending on what was specified on the
         # template.
         if template_format == "json":