Fixed failing examples 415 and 416 in the CommonMark 0.30 spec: empha…

…sis delimiter lengths being multiples of 3. (#108)

Solved by adding a missing condition in Delimiter.closed_by().
Also refactored the function to make it more readable.

mistletoe/core_tokens.py

@@ -438,10 +438,16 @@ def remove(self, n, left=True):
         return True
 
     def closed_by(self, other):
-        return not (self.type[0] != other.type[0]
-                    or (self.open and self.close or other.open and other.close)
-                    and (self.number + other.number) % 3 == 0)
-
+        if self.type[0] != other.type[0]:
+            return False
+        if self.open and self.close or other.open and other.close:
+            # if either of the delimiters can both open and close emphasis, then additional
+            # restrictions apply: the sum of the lengths of the delimiter runs
+            # containing the opening and closing delimiters must not be a multiple of 3
+            # unless both lengths are multiples of 3.
+            return ((self.number + other.number) % 3 != 0
+                    or (self.number % 3 == 0 and other.number % 3 == 0))
+        return True
 
     def __repr__(self):
         if not self.type.startswith(('*', '_')):

test/test_span_token.py

@@ -54,6 +54,11 @@ def test_emphasis_for_asterisk_without_punctuation(self):
         self._test_token(next(tokens), 'an example without', children=True)
         self._test_token(next(tokens), 'punctuation', children=False)
 
+    def test_emphasis_when_both_delimiter_run_lengths_are_multiples_of_3(self):
+        tokens = iter(span_token.tokenize_inner('foo******bar*********baz'))
+        self._test_token(next(tokens), 'foo', children=False)
+        self._test_token(next(tokens), 'bar', children=True)
+        self._test_token(next(tokens), '***baz', children=False)
 
 class TestInlineCode(TestBranchToken):
     def _test_parse_enclosed(self, encl_type, encl_delimiter):