All variables in complex args again

Also updates the CHANGELOG to note the slight change, where bare variables
in args are no longer allowed to be bare variables

Fixes ansible#13518

CHANGELOG.md

@@ -82,6 +82,26 @@ newline being stripped you can change your playbook like this:
     "msg": "Testing some things"
     ```
 
+* When specifying complex args as a variable, the variable must use the full jinja2
+variable syntax ('{{var_name}}') - bare variable names there are no longer accepted.
+In fact, even specifying args with variables has been deprecated, and will not be
+allowed in future versions:
+
+    ```
+    ---
+    - hosts: localhost
+      connection: local
+      gather_facts: false
+      vars:
+        my_dirs:
+          - { path: /tmp/3a, state: directory, mode: 0755 }
+          - { path: /tmp/3b, state: directory, mode: 0700 }
+      tasks:
+        - file:
+          args: "{{item}}"
+          with_items: my_dirs
+    ```
+
 ###Plugins
 
 * Rewritten dnf module that should be faster and less prone to encountering bugs in cornercases

lib/ansible/parsing/mod_args.py

@@ -137,7 +137,16 @@ def _normalize_parameters(self, thing, action=None, additional_args=dict()):
         # than those which may be parsed/normalized next
         final_args = dict()
         if additional_args:
-            final_args.update(additional_args)
+            if isinstance(additional_args, string_types):
+                templar = Templar(loader=None)
+                if templar._contains_vars(additional_args):
+                    final_args['_variable_params'] = additional_args
+                else:
+                    raise AnsibleParserError("Complex args containing variables cannot use bare variables, and must use the full variable style ('{{var_name}}')")
+            elif isinstance(additional_args, dict):
+                final_args.update(additional_args)
+            else:
+                raise AnsibleParserError('Complex args must be a dictionary or variable string ("{{var}}").')
 
         # how we normalize depends if we figured out what the module name is
         # yet.  If we have already figured it out, it's an 'old style' invocation.