Don't unhug things containing only a triple-quoted-string

add_trailing_comma.py

@@ -251,9 +251,14 @@ def _fix_brace(fix_data, add_comma, tokens):
     hug_open = tokens[first_brace + 1].name not in NON_CODING_TOKENS
     hug_close = tokens[last_brace - 1].name not in NON_CODING_TOKENS
     if (
+            # Don't unhug single element things with a multi-line component
+            # inside.
             not fix_data.multi_arg and
             hug_open and
-            tokens[last_brace - 1].src in END_BRACES
+            tokens[last_brace - 1].src in END_BRACES or
+            # Don't unhug when containing a single token (such as a triple
+            # quoted string).
+            first_brace + 2 == last_brace
     ):
         hug_open = hug_close = False
 

tests/add_trailing_comma_test.py

@@ -312,6 +312,10 @@ def test_fixes_defs(src, expected):
         'f([\n'
         '    1, 2, 3,\n'
         '])',
+        # Single triple-quoted-string argument, don't unhug
+        'textwrap.dedent("""\n'
+        '    hi\n'
+        '""")',
     ),
 )
 def test_noop_unhugs(src):