Fix parsing of zero-length tokens

add_trailing_comma.py

@@ -325,6 +325,9 @@ def _fix_src(contents_text, py35_plus, py36_plus):
 
     tokens = src_to_tokens(contents_text)
     for i, token in _changing_list(tokens):
+        # DEDENT is a zero length token
+        if not token.src:
+            continue
         key = Offset(token.line, token.utf8_byte_offset)
 
         fixes = []

tests/add_trailing_comma_test.py

@@ -149,9 +149,13 @@ def test_fixes_calls(src, expected):
         '[1, 2, 3, 4]',
         '{1, 2, 3, 4}',
         '{1: 2, 3: 4}',
+        # Regression test for #26
+        'if True:\n'
+        '    pass\n'
+        '[x] = {y}',
     ),
 )
-def test_noop_one_line_literals(src):
+def test_noop_literals(src):
     assert _fix_src(src, py35_plus=False, py36_plus=False) == src