Handle edge case

The regex up to now could not handle a quoted string inside another, i.e. ('"lala"').

If that string had some % symbol inside ('"%lala"') it already though that the string
was finished and thus the % symbol was the one triggering a %-format string.

Now we check for a single quote or double quoted string.

flake8_pep3101.py

@@ -6,7 +6,19 @@
 except ImportError:
     import pep8 as pycodestyle
 
-OLD_RE = re.compile(r'^(?:[^\'"]*[\'"][^\'"]*[\'"])*\s*%|^\s*%')
+
+OLD_RE = re.compile(
+    r'^'  # beginning of a string
+    r'('  # group
+    r'[^\'"]*'  # any character(s) that is/are no single/double quote
+    r'(\'[^\']*\')*'  # any single quoted string
+    r'("[^"]*")'  # any double quotted string
+    r')*'  # end of group, either none or multiple repetitions
+    r'\s*'  # any space
+    r'%'  # percent character
+    r'|'  # either everything up to now or what comes next
+    r'^\s*%'  # beginning of a string, spaces and a percent character
+)
 
 FORMATTERS = (
     's',
@@ -37,7 +49,8 @@ class Flake8Pep3101(object):
     format string and the parameters to be inserted.
     I never found a reference for that but now sentry relies on it.
     So this check, looks for:
-    1. two string delimiter characters following any number of whitespace and %
+    1. two string delimiter characters following any number of whitespace, a %
+       an and extra space
     2. Beginning of line, any number of whitespace and %
 
     This will ignore log messages that do not do inline message formatting,

run_tests.py

@@ -252,6 +252,14 @@ def test_multiple_strings(self):
         ret = list(checker.run())
         self.assertEqual(len(ret), 0)
 
+    def test_multiple_single_quotes_strings(self):
+        file_path = self._given_a_file_in_test_dir('\n'.join([
+            "'''''''1' if '%' else '2'"
+        ]))
+        checker = Flake8Pep3101(None, file_path)
+        ret = list(checker.run())
+        self.assertEqual(len(ret), 0)
+
     def test_multiple_strings_with_old_formatting(self):
         """Check that multiple quoting is handled properly.
 
@@ -267,6 +275,20 @@ def test_multiple_strings_with_old_formatting(self):
         self.assertEqual(ret[0][1], 14)
         self.assertEqual(ret[0][2], 'S001 found % formatter')
 
+    def test_percent_on_string(self):
+        """Check that multiple quoting is handled properly.
+
+        In this case no string substitution is happening.
+
+        Found in plone.app.drafts.tests
+        """
+        file_path = self._given_a_file_in_test_dir('\n'.join([
+            'a = \'"%2B%2Badd%2B%2BMyDocument"\''
+        ]))
+        checker = Flake8Pep3101(None, file_path)
+        ret = list(checker.run())
+        self.assertEqual(len(ret), 0)
+
 
 if __name__ == '__main__':
     unittest.main()