cli: Add -f colored to force colors

`-f standard` shows non-colored output,
`-f colored` shows colored output,
`-f auto` is the new default, it chooses `standard` or `colored`
depending on terminal capabilities.

tests/test_cli.py

@@ -351,7 +351,7 @@ class CommandLineTestCase(unittest.TestCase):
             '\n' % file))
         self.assertEqual(err, '')
 
-    def test_run_colored_output(self):
+    def test_run_default_format_output_in_tty(self):
         file = os.path.join(self.wd, 'a.yaml')
 
         # Create a pseudo-TTY and redirect stdout to it
@@ -383,3 +383,59 @@ class CommandLineTestCase(unittest.TestCase):
             'no new line character at the end of file  '
             '\033[2m(new-line-at-end-of-file)\033[0m\n'
             '\n' % file))
+
+    def test_run_default_format_output_without_tty(self):
+        file = os.path.join(self.wd, 'a.yaml')
+
+        sys.stdout, sys.stderr = StringIO(), StringIO()
+        with self.assertRaises(SystemExit) as ctx:
+            cli.run((file, ))
+
+        self.assertEqual(ctx.exception.code, 1)
+
+        out, err = sys.stdout.getvalue(), sys.stderr.getvalue()
+        self.assertEqual(out, (
+            '%s\n'
+            '  2:4       error    trailing spaces  (trailing-spaces)\n'
+            '  3:4       error    no new line character at the end of file  '
+            '(new-line-at-end-of-file)\n'
+            '\n' % file))
+        self.assertEqual(err, '')
+
+    def test_run_auto_output_without_tty_output(self):
+        file = os.path.join(self.wd, 'a.yaml')
+
+        sys.stdout, sys.stderr = StringIO(), StringIO()
+        with self.assertRaises(SystemExit) as ctx:
+            cli.run((file, '--format', 'auto'))
+
+        self.assertEqual(ctx.exception.code, 1)
+
+        out, err = sys.stdout.getvalue(), sys.stderr.getvalue()
+        self.assertEqual(out, (
+            '%s\n'
+            '  2:4       error    trailing spaces  (trailing-spaces)\n'
+            '  3:4       error    no new line character at the end of file  '
+            '(new-line-at-end-of-file)\n'
+            '\n' % file))
+        self.assertEqual(err, '')
+
+    def test_run_format_colored(self):
+        file = os.path.join(self.wd, 'a.yaml')
+
+        sys.stdout, sys.stderr = StringIO(), StringIO()
+        with self.assertRaises(SystemExit) as ctx:
+            cli.run((file, '--format', 'colored'))
+
+        self.assertEqual(ctx.exception.code, 1)
+
+        out, err = sys.stdout.getvalue(), sys.stderr.getvalue()
+        self.assertEqual(out, (
+            '\033[4m%s\033[0m\n'
+            '  \033[2m2:4\033[0m       \033[31merror\033[0m    '
+            'trailing spaces  \033[2m(trailing-spaces)\033[0m\n'
+            '  \033[2m3:4\033[0m       \033[31merror\033[0m    '
+            'no new line character at the end of file  '
+            '\033[2m(new-line-at-end-of-file)\033[0m\n'
+            '\n' % file))
+        self.assertEqual(err, '')

yamllint/cli.py

@@ -96,8 +96,8 @@ def run(argv=None):
                               action='store',
                               help='custom configuration (as YAML source)')
     parser.add_argument('-f', '--format',
-                        choices=('parsable', 'standard'), default='standard',
+                        choices=('parsable', 'standard', 'colored', 'auto'),
-                        help='format for parsing output')
+                        default='auto', help='format for parsing output')
     parser.add_argument('-s', '--strict',
                         action='store_true',
                         help='return non-zero exit code on warnings '
@@ -143,7 +143,8 @@ def run(argv=None):
                 for problem in linter.run(f, conf, filepath):
                     if args.format == 'parsable':
                         print(Format.parsable(problem, file))
-                    elif supports_color():
+                    elif args.format == 'colored' or \
+                            (args.format == 'auto' and supports_color()):
                         if first:
                             print('\033[4m%s\033[0m' % file)
                             first = False