Add ability to turn checks off by default

flake8/engine.py

@@ -19,6 +19,7 @@ def _register_extensions():
     extensions.add(('pep8', pep8.__version__))
     parser_hooks = []
     options_hooks = []
+    ignored_hooks = []
     try:
         from pkg_resources import iter_entry_points
     except ImportError:
@@ -32,7 +33,9 @@ def _register_extensions():
                 parser_hooks.append(checker.add_options)
             if hasattr(checker, 'parse_options'):
                 options_hooks.append(checker.parse_options)
-    return extensions, parser_hooks, options_hooks
+            if getattr(checker, 'off_by_default', False) is True:
+                ignored_hooks.append(entry.name)
+    return extensions, parser_hooks, options_hooks, ignored_hooks
 
 
 def _install_hook_cb(option, option_str, value, parser):
@@ -52,7 +55,7 @@ def get_parser():
     """This returns an instance of optparse.OptionParser with all the
     extensions registered and options set. This wraps ``pep8.get_parser``.
     """
-    (extensions, parser_hooks, options_hooks) = _register_extensions()
+    (extensions, parser_hooks, options_hooks, ignored) = _register_extensions()
     details = ', '.join(['%s: %s' % ext for ext in extensions])
     python_version = get_python_version()
     parser = pep8.get_parser('flake8', '%s (%s) %s' % (
@@ -79,6 +82,7 @@ def get_parser():
                       help='Install the appropriate hook for this '
                       'repository.', action='callback',
                       callback=_install_hook_cb)
+    parser.ignored_extensions = ignored
     return parser, options_hooks
 
 
@@ -96,6 +100,14 @@ class StyleGuide(pep8.StyleGuide):
         return fchecker.check_all(expected=expected, line_offset=line_offset)
 
 
+def _disable_extensions(parser, options):
+    select = set(options.select)
+    ignore = set(options.ignore)
+    ignore.update(getattr(parser, 'ignored_extensions', []))
+    ignore -= select
+    options.ignore = tuple(ignore)
+
+
 def get_style_guide(**kwargs):
     """Parse the options and configure the checker. This returns a sub-class
     of ``pep8.StyleGuide``."""
@@ -103,6 +115,8 @@ def get_style_guide(**kwargs):
     styleguide = StyleGuide(**kwargs)
     options = styleguide.options
 
+    _disable_extensions(kwargs['parser'], options)
+
     if options.exclude and not isinstance(options.exclude, list):
         options.exclude = pep8.normalize_paths(options.exclude)
     elif not options.exclude:

flake8/tests/test_engine.py

@@ -28,7 +28,7 @@ class TestEngine(unittest.TestCase):
 
     def test_get_style_guide(self):
         with mock.patch('flake8.engine._register_extensions') as reg_ext:
-            reg_ext.return_value = ([], [], [])
+            reg_ext.return_value = ([], [], [], [])
             g = engine.get_style_guide()
             self.assertTrue(isinstance(g, engine.StyleGuide))
             reg_ext.assert_called_once_with()
@@ -37,6 +37,7 @@ class TestEngine(unittest.TestCase):
         m = mock.Mock()
         with mock.patch('flake8.engine.StyleGuide') as StyleGuide:
             with mock.patch('flake8.engine.get_parser') as get_parser:
+                m.ignored_extensions = []
                 StyleGuide.return_value.options.jobs = '42'
                 get_parser.return_value = (m, [])
                 engine.get_style_guide(foo='bar')
@@ -58,7 +59,8 @@ class TestEngine(unittest.TestCase):
         gpv = self.start_patch('flake8.engine.get_python_version')
         pgp = self.start_patch('pep8.get_parser')
         m = mock.Mock()
-        re.return_value = ([('pyflakes', '0.7'), ('mccabe', '0.2')], [], [])
+        re.return_value = ([('pyflakes', '0.7'), ('mccabe', '0.2')], [], [],
+                           [])
         gpv.return_value = 'Python Version'
         pgp.return_value = m
         # actual call we're testing
@@ -94,5 +96,20 @@ class TestEngine(unittest.TestCase):
             guide = engine.get_style_guide()
             assert isinstance(guide, reporter.BaseQReport) is False
 
+    def test_disables_extensions_that_are_not_selected(self):
+        with mock.patch('flake8.engine._register_extensions') as re:
+            re.return_value = ([('fake_ext', '0.1a1')], [], [], ['X'])
+            sg = engine.get_style_guide()
+            assert 'X' in sg.options.ignore
+
+    def test_enables_off_by_default_extensions(self):
+        with mock.patch('flake8.engine._register_extensions') as re:
+            re.return_value = ([('fake_ext', '0.1a1')], [], [], ['X'])
+            parser, options = engine.get_parser()
+            parser.parse_args(['--select=X'])
+            sg = engine.StyleGuide(parser=parser)
+            assert 'X' not in sg.options.ignore
+
+
 if __name__ == '__main__':
     unittest.main()