templar: ensure that exceptions are handled, fix 'AttributeError' (#48792)

* templar: ensure that exceptions are handled

* Fix AttributeError: object has no attribute 'message'

'message' attribute is deprecated since Python 2.6 and not available
with Python 3.

Simple reproducer:

    - hosts: localhost
      vars:
        not_json: "{{ 'test str' | from_json }}"
      tasks:
        - command: "echo {{ not_json }}"

lib/ansible/template/vars.py

@@ -107,7 +107,7 @@ class AnsibleJ2Vars(Mapping):
             except AnsibleUndefinedVariable:
                 raise
             except Exception as e:
-                msg = getattr(e, 'message') or to_native(e)
+                msg = getattr(e, 'message', None) or to_native(e)
                 raise AnsibleError("An unhandled exception occurred while templating '%s'. "
                                    "Error was a %s, original message: %s" % (to_native(variable), type(e), msg))
 

test/units/template/test_templar.py

@@ -50,6 +50,7 @@ class BaseTemplar(object):
             some_unsafe_var=wrap_var("unsafe_blip"),
             some_static_unsafe_var=wrap_var("static_unsafe_blip"),
             some_unsafe_keyword=wrap_var("{{ foo }}"),
+            str_with_error="{{ 'str' | from_json }}",
         )
         self.fake_loader = DictDataLoader({
             "/path/to/my_file.txt": "foo\n",
@@ -183,6 +184,10 @@ class TestTemplarTemplate(BaseTemplar, unittest.TestCase):
                                 self.templar.template,
                                 data)
 
+    def test_template_with_error(self):
+        """Check that AnsibleError is raised, fail if an unhandled exception is raised"""
+        self.assertRaises(AnsibleError, self.templar.template, "{{ str_with_error }}")
+
 
 class TestTemplarMisc(BaseTemplar, unittest.TestCase):
     def test_templar_simple(self):