Fixed #27783 -- Switched VariableDoesNotExist.__str__() to repr() context.

Using __str__() and then repr'ing the result looks strange and can lead
to recursive rendering of forms.

django/template/base.py

@@ -119,7 +119,7 @@ class VariableDoesNotExist(Exception):
         self.params = params
 
     def __str__(self):
-        return self.msg % tuple(force_text(p, errors='replace') for p in self.params)
+        return self.msg % self.params
 
 
 class Origin:

tests/template_tests/test_base.py

+from django.template.base import VariableDoesNotExist
+from django.test import SimpleTestCase
+
+
+class VariableDoesNotExistTests(SimpleTestCase):
+    def test_str(self):
+        exc = VariableDoesNotExist(msg='Failed lookup in %r', params=({'foo': 'bar'},))
+        self.assertEqual(str(exc), "Failed lookup in {'foo': 'bar'}")

tests/template_tests/test_logging.py

@@ -75,7 +75,7 @@ class VariableResolveLoggingTests(BaseTemplateLoggingTestCase):
         raised_exception = self.test_handler.log_record.exc_info[1]
         self.assertEqual(
             str(raised_exception),
-            'Failed lookup for key [author] in %r' % ("{%r: %r}" % ('section', 'News'))
+            "Failed lookup for key [author] in {'section': 'News'}"
         )
 
     def test_no_log_when_variable_exists(self):