Merge branch 'bug/67' into 'master'

Remove enabled extensions from `options.select`

When taking advantage of the --select flag for off-by-default
extensions, we neglected to take into account the fact that leaving the
extension names in the select list would cause different behaviour in
pep8. This should remedy this.

Related to GitLab bug #67

----

cc @joe-gordon0

See merge request !37

flake8/engine.py

@@ -98,6 +98,11 @@ def get_parser():
                       help='Redirect report to a file.',
                       type='string', nargs=1, action='callback',
                       callback=callbacks.redirect_stdout)
+    parser.add_option('--enable-extensions', default='',
+                      dest='enabled_extensions',
+                      help='Enable plugins and extensions that are disabled '
+                           'by default',
+                      type='string')
     parser.ignored_extensions = ignored
     return parser, options_hooks
 
@@ -186,11 +191,32 @@ class StyleGuide(object):
         )
 
 
+def _parse_multi_options(options, split_token=','):
+    r"""Split and strip and discard empties.
+
+    Turns the following:
+
+    A,
+    B,
+
+    into ["A", "B"].
+
+    Credit: Kristian Glass as contributed to pep8
+    """
+    if options:
+        return [o.strip() for o in options.split(split_token) if o.strip()]
+    else:
+        return options
+
+
 def _disable_extensions(parser, options):
     ignored_extensions = set(getattr(parser, 'ignored_extensions', []))
+    enabled = set(_parse_multi_options(options.enabled_extensions))
+
     # Remove any of the selected extensions from the extensions ignored by
     # default.
-    ignored_extensions -= set(options.select)
+    ignored_extensions -= enabled
+
     # Whatever is left afterwards should be unioned with options.ignore and
     # options.ignore should be updated with that.
     options.ignore = tuple(ignored_extensions.union(options.ignore))

flake8/tests/test_engine.py

@@ -56,6 +56,18 @@ class TestEngine(unittest.TestCase):
                 self.assertTrue(isinstance(i, list))
             self.assertTrue(register_check.called)
 
+    def test_disable_extensions(self):
+        parser = mock.MagicMock()
+        options = mock.MagicMock()
+
+        parser.ignored_extensions = ['I123', 'I345', 'I678', 'I910']
+
+        options.enabled_extensions = 'I345,\nI678,I910'
+        options.ignore = ('E121', 'E123')
+
+        engine._disable_extensions(parser, options)
+        self.assertEqual(set(options.ignore), set(['E121', 'E123', 'I123']))
+
     def test_get_parser(self):
         # setup
         re = self.start_patch('flake8.engine._register_extensions')