Warn when jinja2 delimiters are found in a when statement (#20312)

* Warn when jinja2 delimiters are found in a when statement

* Use templar._clean_data to look for templating

lib/ansible/playbook/conditional.py

@@ -32,6 +32,12 @@ from ansible.template import Templar
 from ansible.template.safe_eval import safe_eval
 from ansible.module_utils._text import to_native
 
+try:
+    from __main__ import display
+except ImportError:
+    from ansible.utils.display import Display
+    display = Display()
+
 DEFINED_REGEX = re.compile(r'(hostvars\[.+\]|[\w_]+)\s+(not\s+is|is|is\s+not)\s+(defined|undefined)')
 LOOKUP_REGEX = re.compile(r'lookup\s*\(')
 VALID_VAR_REGEX = re.compile("^[_A-Za-z][_a-zA-Z0-9]*$")
@@ -132,6 +138,11 @@ class Conditional:
         if conditional in all_vars and VALID_VAR_REGEX.match(conditional):
             conditional = all_vars[conditional]
 
+        if templar._clean_data(conditional) != conditional:
+            display.warning('when statements should not include jinja2 '
+                            'templating delimiters such as {{ }} or {%% %%}. '
+                            'Found: %s' % conditional)
+
         # make sure the templar is using the variables specified with this method
         templar.set_available_variables(variables=all_vars)