Simplify word boundaries (#1060)

Use lookahead/lookbehind matching to ensure there is whitespace around the
token. Replaces the use of \b, which doesn't work for "ft.", etc.

beets/util/__init__.py

@@ -686,12 +686,9 @@ def feat_tokens(for_artist=True):
     The `for_artist` option determines whether the regex should be
     suitable for matching artist fields (the default) or title fields.
     """
-    feat_special_chars = ['&', 'feat.', 'ft.']
     feat_words = ['ft', 'featuring', 'feat']
-    if for_artist:  # appending to artist name enables more tokens
-        feat_words += ['with', 'vs', 'and', 'con']
-    regex = r'%s' % '|'.join(['\\b%s\\b' % re.escape(x) for x in feat_words])
     if for_artist:
-        regex = r'%s|%s' % \
-            ('|'.join([re.escape(x) for x in feat_special_chars]), regex)
-    return '(?:{0})'.format(regex)
+        feat_words += ['with', 'vs', 'and', 'con', '&', 'feat.', 'ft.']
+    return '(?<=\s)(?:{0})(?=\s)'.format(
+        '|'.join(re.escape(x) for x in feat_words)
+    )

test/test_ftintitle.py

@@ -50,6 +50,7 @@ def test_contains_feat(self):
         self.assertTrue(ftintitle.contains_feat('Alice and Bob'))
         self.assertTrue(ftintitle.contains_feat('Alice With Bob'))
         self.assertFalse(ftintitle.contains_feat('Alice defeat Bob'))
+        self.assertFalse(ftintitle.contains_feat('Aliceft.Bob'))
 
 
 def suite():