Fix SPLIT_ARGUMENTS_WHEN_COMMA_TERMINATED for one-item argument lists (…

…#1142)

Turn

r = f0(1,)
into

r = f0(
    1,
)

in case SPLIT_ARGUMENTS_WHEN_COMMA_TERMINATED is enabled

CHANGELOG.md

@@ -8,7 +8,9 @@
   by removing the "verify" parameter.
 - Changed FORCE_MULTILINE_DICT to override SPLIT_ALL_TOP_LEVEL_COMMA_SEPARATED_VALUES.
 - Adopt pyproject.toml (PEP 517) for build system
+### Fixed
 - Do not treat variables named `match` as the match keyword
+- Fix SPLIT_ARGUMENTS_WHEN_COMMA_TERMINATED for one-item argument lists.
 
 ## [0.40.1] 2023-06-20
 ### Fixed

yapf/yapflib/reformatter.py

@@ -245,8 +245,13 @@ def _CanPlaceOnSingleLine(line):
   Returns:
     True if the line can or should be added to a single line. False otherwise.
   """
-  token_names = [x.name for x in line.tokens]
-  if (style.Get('FORCE_MULTILINE_DICT') and 'LBRACE' in token_names):
+  token_types = [x.type for x in line.tokens]
+  if (style.Get('SPLIT_ARGUMENTS_WHEN_COMMA_TERMINATED') and
+      any(token_types[token_index - 1] == token.COMMA
+          for token_index, token_type in enumerate(token_types[1:], start=1)
+          if token_type == token.RPAR)):
+    return False
+  if (style.Get('FORCE_MULTILINE_DICT') and token.LBRACE in token_types):
     return False
   indent_amt = style.Get('INDENT_WIDTH') * line.depth
   last = line.last

yapftests/reformatter_basic_test.py

@@ -2275,6 +2275,8 @@ def testSplittingArgumentsTerminatedByComma(self):
         a_very_long_function_name(long_argument_name_1, long_argument_name_2, long_argument_name_3, long_argument_name_4,)
 
         r =f0 (1,  2,3,)
+
+        r =f0 (1,)
     """)  # noqa
     expected_formatted_code = textwrap.dedent("""\
         function_name(argument_name_1=1, argument_name_2=2, argument_name_3=3)
@@ -2303,6 +2305,10 @@ def testSplittingArgumentsTerminatedByComma(self):
             2,
             3,
         )
+
+        r = f0(
+            1,
+        )
     """)
 
     try: