Fix bug with CRLF in new-lines and require-starting-space

Pound-signs followed by a lone CRLF should not
raise if require-starting-space is specified.

If require-starting-space is true, *and* either:
- new-lines: disbale, or
- newlines: type: dos
is specified, a line with `#\r` or `#\r\n` should
not raise a false positive.

This commit also uses a Set for O(1) membership testing
and uses the correct escape sequence for the nul byte.

If we find a CRLF when looking for Unix newlines, yamllint
should always raise, regardless of logic with
require-starting-space.

Closes: Issue #171.

tests/rules/test_comments.py

@@ -186,6 +186,27 @@ class CommentsTestCase(RuleTestCase):
                    'inline: comment  #\n'
                    'foo: bar\n', conf)
 
+    def test_empty_comment_crlf_dos_newlines(self):
+        conf = ('comments:\n'
+                '  require-starting-space: true\n'
+                '  min-spaces-from-content: 2\n'
+                'new-lines:\n'
+                '  type: dos\n')
+        self.check('---\r\n'
+                   '# This is paragraph 1.\r\n'
+                   '#\r\n'
+                   '# This is paragraph 2.\r\n', conf)
+
+    def test_empty_comment_crlf_disabled_newlines(self):
+        conf = ('comments:\n'
+                '  require-starting-space: true\n'
+                '  min-spaces-from-content: 2\n'
+                'new-lines: disable\n')
+        self.check('---\r\n'
+                   '# This is paragraph 1.\r\n'
+                   '#\r\n'
+                   '# This is paragraph 2.\r\n', conf)
+
     def test_first_line(self):
         conf = ('comments:\n'
                 '  require-starting-space: true\n'

tests/rules/test_new_lines.py

@@ -40,6 +40,16 @@ class NewLinesTestCase(RuleTestCase):
         self.check('---\ntext\n', conf)
         self.check('---\r\ntext\r\n', conf, problem=(1, 4))
 
+    def test_unix_type_required_st_sp(self):
+        # If we find a CRLF when looking for Unix newlines, yamllint
+        # should always raise, regardless of logic with
+        # require-starting-space.
+        conf = ('new-line-at-end-of-file: disable\n'
+                'new-lines: {type: unix}\n'
+                'comments:\n'
+                '  require-starting-space: true\n')
+        self.check('---\r\n#\r\n', conf, problem=(1, 4))
+
     def test_dos_type(self):
         conf = ('new-line-at-end-of-file: disable\n'
                 'new-lines: {type: dos}\n')

yamllint/rules/comments.py

@@ -97,7 +97,9 @@ def check(conf, comment):
                     comment.column_no == 1 and
                     re.match(r'^!\S', comment.buffer[text_start:])):
                 return
-            elif comment.buffer[text_start] not in (' ', '\n', '\0'):
+            # We can test for both \r and \r\n just by checking first char
+            # \r itself is a valid newline on some older OS.
+            elif comment.buffer[text_start] not in {' ', '\n', '\r', '\x00'}:
                 column = comment.column_no + text_start - comment.pointer
                 yield LintProblem(comment.line_no,
                                   column,