Config: Allow 'enable' keyword for rules

In the same manner as 'disable', 'enable' allows setting a rule on
without worrying about its options.

tests/rules/test_comments_indentation.py

@@ -49,7 +49,7 @@ class CommentsIndentationTestCase(RuleTestCase):
                    '...\n', conf)
 
     def test_enabled(self):
-        conf = 'comments-indentation: {}'
+        conf = 'comments-indentation: enable'
         self.check('---\n'
                    '# line 1\n'
                    '# line 2\n', conf)
@@ -123,18 +123,18 @@ class CommentsIndentationTestCase(RuleTestCase):
                    '...\n', conf)
 
     def test_first_line(self):
-        conf = 'comments-indentation: {}'
+        conf = 'comments-indentation: enable'
         self.check('# comment\n', conf)
         self.check('  # comment\n', conf, problem=(1, 3))
 
     def test_no_newline_at_end(self):
-        conf = ('comments-indentation: {}\n'
+        conf = ('comments-indentation: enable\n'
                 'new-line-at-end-of-file: disable\n')
         self.check('# comment', conf)
         self.check('  # comment', conf, problem=(1, 3))
 
     def test_empty_comment(self):
-        conf = 'comments-indentation: {}'
+        conf = 'comments-indentation: enable'
         self.check('---\n'
                    '# hey\n'
                    '# normal\n'

tests/rules/test_key_duplicates.py

@@ -80,7 +80,7 @@ class KeyDuplicatesTestCase(RuleTestCase):
                    ': 1\n', conf)
 
     def test_enabled(self):
-        conf = 'key-duplicates: {}'
+        conf = 'key-duplicates: enable'
         self.check('---\n'
                    'block mapping:\n'
                    '  key: a\n'
@@ -149,7 +149,7 @@ class KeyDuplicatesTestCase(RuleTestCase):
                    problem4=(7, 3))
 
     def test_key_tokens_in_flow_sequences(self):
-        conf = 'key-duplicates: {}'
+        conf = 'key-duplicates: enable'
         self.check('---\n'
                    '[\n'
                    '  flow: sequence, with, key: value, mappings\n'

tests/rules/test_new_line_at_end_of_file.py

@@ -30,7 +30,7 @@ class NewLineAtEndOfFileTestCase(RuleTestCase):
         self.check('Sentence.\n', conf)
 
     def test_enabled(self):
-        conf = ('new-line-at-end-of-file: {}\n'
+        conf = ('new-line-at-end-of-file: enable\n'
                 'empty-lines: disable\n'
                 'document-start: disable\n')
         self.check('', conf)

tests/rules/test_trailing_spaces.py

@@ -29,7 +29,7 @@ class TrailingSpacesTestCase(RuleTestCase):
                    'some: text \n', conf)
 
     def test_enabled(self):
-        conf = 'trailing-spaces: {}'
+        conf = 'trailing-spaces: enable'
         self.check('', conf)
         self.check('\n', conf)
         self.check('    \n', conf, problem=(1, 1))
@@ -40,7 +40,7 @@ class TrailingSpacesTestCase(RuleTestCase):
                    'some: text\t\n', conf, problem=(2, 11, 'syntax'))
 
     def test_with_dos_new_lines(self):
-        conf = ('trailing-spaces: {}\n'
+        conf = ('trailing-spaces: enable\n'
                 'new-lines: {type: dos}\n')
         self.check('---\r\n'
                    'some: text\r\n', conf)

tests/test_config.py

@@ -37,7 +37,7 @@ class SimpleConfigTestCase(unittest.TestCase):
                 config.YamlLintConfigError,
                 'invalid config: no such rule: "this-one-does-not-exist"'):
             config.YamlLintConfig('rules:\n'
-                                  '  this-one-does-not-exist: {}\n')
+                                  '  this-one-does-not-exist: enable\n')
 
     def test_missing_option(self):
         with self.assertRaisesRegexp(
@@ -65,6 +65,11 @@ class SimpleConfigTestCase(unittest.TestCase):
         self.assertEqual(config.validate_rule_conf(Rule, False), False)
         self.assertEqual(config.validate_rule_conf(Rule, 'disable'), False)
 
+        self.assertEqual(config.validate_rule_conf(Rule, {}),
+                         {'level': 'error'})
+        self.assertEqual(config.validate_rule_conf(Rule, 'enable'),
+                         {'level': 'error'})
+
         config.validate_rule_conf(Rule, {'level': 'error'})
         config.validate_rule_conf(Rule, {'level': 'warning'})
         self.assertRaises(config.YamlLintConfigError,