logical_line.py

# Copyright 2015 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""LogicalLine primitive for formatting.

A logical line is the containing data structure produced by the parser. It
collects all nodes (stored in FormatToken objects) that could appear on a single
line if there were no line length restrictions. It's then used by the parser to
perform the wrapping required to comply with the style guide.
"""

from yapf_third_party._ylib2to3.fixer_util import syms as python_symbols

from yapf.pytree import pytree_utils
from yapf.pytree import split_penalty
from yapf.yapflib import format_token
from yapf.yapflib import style
from yapf.yapflib import subtypes


class LogicalLine(object):
  """Represents a single logical line in the output.

  Attributes:
    depth: indentation depth of this line. This is just a numeric value used to
      distinguish lines that are more deeply nested than others. It is not the
      actual amount of spaces, which is style-dependent.
  """

  def __init__(self, depth, tokens=None):
    """Constructor.

    Creates a new logical line with the given depth an initial list of tokens.
    Constructs the doubly-linked lists for format tokens using their built-in
    next_token and previous_token attributes.

    Arguments:
      depth: indentation depth of this line
      tokens: initial list of tokens
    """
    self.depth = depth
    self._tokens = tokens or []
    self.disable = False

    if self._tokens:
      # Set up a doubly linked list.
      for index, tok in enumerate(self._tokens[1:]):
        # Note, 'index' is the index to the previous token.
        tok.previous_token = self._tokens[index]
        self._tokens[index].next_token = tok

  def CalculateFormattingInformation(self):
    """Calculate the split penalty and total length for the tokens."""
    # Say that the first token in the line should have a space before it. This
    # means only that if this logical line is joined with a predecessor line,
    # then there will be a space between them.
    self.first.spaces_required_before = 1
    self.first.total_length = len(self.first.value)

    prev_token = self.first
    prev_length = self.first.total_length
    for token in self._tokens[1:]:
      if (token.spaces_required_before == 0 and
          _SpaceRequiredBetween(prev_token, token, self.disable)):
        token.spaces_required_before = 1

      tok_len = len(token.value) if not token.is_pseudo else 0

      spaces_required_before = token.spaces_required_before
      if isinstance(spaces_required_before, list):
        assert token.is_comment, token

        # If here, we are looking at a comment token that appears on a line
        # with other tokens (but because it is a comment, it is always the last
        # token).  Rather than specifying the actual number of spaces here,
        # hard code a value of 0 and then set it later. This logic only works
        # because this comment token is guaranteed to be the last token in the
        # list.
        spaces_required_before = 0

      token.total_length = prev_length + tok_len + spaces_required_before

      # The split penalty has to be computed before {must|can}_break_before,
      # because these may use it for their decision.
      token.split_penalty += _SplitPenalty(prev_token, token)
      token.must_break_before = _MustBreakBefore(prev_token, token)
      token.can_break_before = (
          token.must_break_before or _CanBreakBefore(prev_token, token))

      prev_length = token.total_length
      prev_token = token

  def Split(self):
    """Split the line at semicolons."""
    if not self.has_semicolon or self.disable:
      return [self]

    llines = []
    lline = LogicalLine(self.depth)
    for tok in self._tokens:
      if tok.value == ';':
        llines.append(lline)
        lline = LogicalLine(self.depth)
      else:
        lline.AppendToken(tok)

    if lline.tokens:
      llines.append(lline)

    for lline in llines:
      lline.first.previous_token = None
      lline.last.next_token = None

    return llines

  ############################################################################
  # Token Access and Manipulation Methods                                    #
  ############################################################################

  def AppendToken(self, token):
    """Append a new FormatToken to the tokens contained in this line."""
    if self._tokens:
      token.previous_token = self.last
      self.last.next_token = token
    self._tokens.append(token)

  @property
  def first(self):
    """Returns the first non-whitespace token."""
    return self._tokens[0]

  @property
  def last(self):
    """Returns the last non-whitespace token."""
    return self._tokens[-1]

  ############################################################################
  # Token -> String Methods                                                  #
  ############################################################################

  def AsCode(self, indent_per_depth=2):
    """Return a "code" representation of this line.

    The code representation shows how the line would be printed out as code.

    TODO(eliben): for now this is rudimentary for debugging - once we add
    formatting capabilities, this method will have other uses (not all tokens
    have spaces around them, for example).

    Arguments:
      indent_per_depth: how much spaces to indent per depth level.

    Returns:
      A string representing the line as code.
    """
    indent = ' ' * indent_per_depth * self.depth
    tokens_str = ' '.join(tok.value for tok in self._tokens)
    return indent + tokens_str

  def __str__(self):  # pragma: no cover
    return self.AsCode()

  def __repr__(self):  # pragma: no cover
    tokens_repr = ','.join(
        '{0}({1!r})'.format(tok.name, tok.value) for tok in self._tokens)
    return 'LogicalLine(depth={0}, tokens=[{1}])'.format(
        self.depth, tokens_repr)

  ############################################################################
  # Properties                                                               #
  ############################################################################

  @property
  def tokens(self):
    """Access the tokens contained within this line.

    The caller must not modify the tokens list returned by this method.

    Returns:
      List of tokens in this line.
    """
    return self._tokens

  @property
  def lineno(self):
    """Return the line number of this logical line.

    Returns:
      The line number of the first token in this logical line.
    """
    return self.first.lineno

  @property
  def start(self):
    """The start of the logical line.

    Returns:
      A tuple of the starting line number and column.
    """
    return (self.first.lineno, self.first.column)

  @property
  def end(self):
    """The end of the logical line.

    Returns:
      A tuple of the ending line number and column.
    """
    return (self.last.lineno, self.last.column + len(self.last.value))

  @property
  def is_comment(self):
    return self.first.is_comment

  @property
  def has_semicolon(self):
    return any(tok.value == ';' for tok in self._tokens)


def _IsIdNumberStringToken(tok):
  return tok.is_keyword or tok.is_name or tok.is_number or tok.is_string


def _IsUnaryOperator(tok):
  return subtypes.UNARY_OPERATOR in tok.subtypes


def _HasPrecedence(tok):
  """Whether a binary operation has precedence within its context."""
  node = tok.node

  # We let ancestor be the statement surrounding the operation that tok is the
  # operator in.
  ancestor = node.parent.parent

  while ancestor is not None:
    # Search through the ancestor nodes in the parse tree for operators with
    # lower precedence.
    predecessor_type = pytree_utils.NodeName(ancestor)
    if predecessor_type in ['arith_expr', 'term']:
      # An ancestor "arith_expr" or "term" means we have found an operator
      # with lower precedence than our tok.
      return True
    if predecessor_type != 'atom':
      # We understand the context to look for precedence within as an
      # arbitrary nesting of "arith_expr", "term", and "atom" nodes. If we
      # leave this context we have not found a lower precedence operator.
      return False
    # Under normal usage we expect a complete parse tree to be available and
    # we will return before we get an AttributeError from the root.
    ancestor = ancestor.parent


def _PriorityIndicatingNoSpace(tok):
  """Whether to remove spaces around an operator due to precedence."""
  if not tok.is_arithmetic_op or not tok.is_simple_expr:
    # Limit space removal to highest priority arithmetic operators
    return False
  return _HasPrecedence(tok)


def _IsSubscriptColonAndValuePair(token1, token2):
  return (token1.is_number or token1.is_name) and token2.is_subscript_colon


def _SpaceRequiredBetween(left, right, is_line_disabled):
  """Return True if a space is required between the left and right token."""
  lval = left.value
  rval = right.value
  if (left.is_pseudo and _IsIdNumberStringToken(right) and
      left.previous_token and _IsIdNumberStringToken(left.previous_token)):
    # Space between keyword... tokens and pseudo parens.
    return True
  if left.is_pseudo or right.is_pseudo:
    # There should be a space after the ':' in a dictionary.
    if left.OpensScope():
      return True
    # The closing pseudo-paren shouldn't affect spacing.
    return False
  if left.is_continuation or right.is_continuation:
    # The continuation node's value has all of the spaces it needs.
    return False
  if right.name in pytree_utils.NONSEMANTIC_TOKENS:
    # No space before a non-semantic token.
    return False
  if _IsIdNumberStringToken(left) and _IsIdNumberStringToken(right):
    # Spaces between keyword, string, number, and identifier tokens.
    return True
  if lval == ',' and rval == ':':
    # We do want a space between a comma and colon.
    return True
  if style.Get('SPACE_INSIDE_BRACKETS'):
    # Supersede the "no space before a colon or comma" check.
    if left.OpensScope() and rval == ':':
      return True
    if right.ClosesScope() and lval == ':':
      return True
  if (style.Get('SPACES_AROUND_SUBSCRIPT_COLON') and
      (_IsSubscriptColonAndValuePair(left, right) or
       _IsSubscriptColonAndValuePair(right, left))):
    # Supersede the "never want a space before a colon or comma" check.
    return True
  if rval in ':,':
    # Otherwise, we never want a space before a colon or comma.
    return False
  if lval == ',' and rval in ']})':
    # Add a space between ending ',' and closing bracket if requested.
    return style.Get('SPACE_BETWEEN_ENDING_COMMA_AND_CLOSING_BRACKET')
  if lval == ',':
    # We want a space after a comma.
    return True
  if lval == 'from' and rval == '.':
    # Space before the '.' in an import statement.
    return True
  if lval == '.' and rval == 'import':
    # Space after the '.' in an import statement.
    return True
  if (lval == '=' and rval in {'.', ',,,'} and
      subtypes.DEFAULT_OR_NAMED_ASSIGN not in left.subtypes):
    # Space between equal and '.' as in "X = ...".
    return True
  if lval == ':' and rval in {'.', '...'}:
    # Space between : and ...
    return True
  if ((right.is_keyword or right.is_name) and
      (left.is_keyword or left.is_name)):
    # Don't merge two keywords/identifiers.
    return True
  if (subtypes.SUBSCRIPT_COLON in left.subtypes or
      subtypes.SUBSCRIPT_COLON in right.subtypes):
    # A subscript shouldn't have spaces separating its colons.
    return False
  if (subtypes.TYPED_NAME in left.subtypes or
      subtypes.TYPED_NAME in right.subtypes):
    # A typed argument should have a space after the colon.
    return True
  if left.is_string:
    if (rval == '=' and
        subtypes.DEFAULT_OR_NAMED_ASSIGN_ARG_LIST in right.subtypes):
      # If there is a type hint, then we don't want to add a space between the
      # equal sign and the hint.
      return False
    if rval not in '[)]}.' and not right.is_binary_op:
      # A string followed by something other than a subscript, closing bracket,
      # dot, or a binary op should have a space after it.
      return True
    if right.ClosesScope():
      # A string followed by closing brackets should have a space after it
      # depending on SPACE_INSIDE_BRACKETS.  A string followed by opening
      # brackets, however, should not.
      return style.Get('SPACE_INSIDE_BRACKETS')
    if subtypes.SUBSCRIPT_BRACKET in right.subtypes:
      # It's legal to do this in Python: 'hello'[a]
      return False
  if left.is_binary_op and lval != '**' and _IsUnaryOperator(right):
    # Space between the binary operator and the unary operator.
    return True
  if left.is_keyword and _IsUnaryOperator(right):
    # Handle things like "not -3 < x".
    return True
  if _IsUnaryOperator(left) and _IsUnaryOperator(right):
    # No space between two unary operators.
    return False
  if left.is_binary_op or right.is_binary_op:
    if lval == '**' or rval == '**':
      # Space around the "power" operator.
      return style.Get('SPACES_AROUND_POWER_OPERATOR')
    # Enforce spaces around binary operators except the blocked ones.
    block_list = style.Get('NO_SPACES_AROUND_SELECTED_BINARY_OPERATORS')
    if lval in block_list or rval in block_list:
      return False
    if style.Get('ARITHMETIC_PRECEDENCE_INDICATION'):
      if _PriorityIndicatingNoSpace(left) or _PriorityIndicatingNoSpace(right):
        return False
      else:
        return True
    else:
      return True
  if (_IsUnaryOperator(left) and lval != 'not' and
      (right.is_name or right.is_number or rval == '(')):
    # The previous token was a unary op. No space is desired between it and
    # the current token.
    return False
  if (subtypes.DEFAULT_OR_NAMED_ASSIGN in left.subtypes and
      subtypes.TYPED_NAME not in right.subtypes):
    # A named argument or default parameter shouldn't have spaces around it.
    return style.Get('SPACES_AROUND_DEFAULT_OR_NAMED_ASSIGN')
  if (subtypes.DEFAULT_OR_NAMED_ASSIGN in right.subtypes and
      subtypes.TYPED_NAME not in left.subtypes):
    # A named argument or default parameter shouldn't have spaces around it.
    return style.Get('SPACES_AROUND_DEFAULT_OR_NAMED_ASSIGN')
  if (subtypes.VARARGS_LIST in left.subtypes or
      subtypes.VARARGS_LIST in right.subtypes):
    return False
  if (subtypes.VARARGS_STAR in left.subtypes or
      subtypes.KWARGS_STAR_STAR in left.subtypes):
    # Don't add a space after a vararg's star or a keyword's star-star.
    return False
  if lval == '@' and subtypes.DECORATOR in left.subtypes:
    # Decorators shouldn't be separated from the 'at' sign.
    return False
  if left.is_keyword and rval == '.':
    # Add space between keywords and dots.
    return lval not in {'None', 'print'}
  if lval == '.' and right.is_keyword:
    # Add space between keywords and dots.
    return rval not in {'None', 'print'}
  if lval == '.' or rval == '.':
    # Don't place spaces between dots.
    return False
  if ((lval == '(' and rval == ')') or (lval == '[' and rval == ']') or
      (lval == '{' and rval == '}')):
    # Empty objects shouldn't be separated by spaces.
    return False
  if not is_line_disabled and (left.OpensScope() or right.ClosesScope()):
    if (style.GetOrDefault('SPACES_AROUND_DICT_DELIMITERS', False) and (
        (lval == '{' and _IsDictListTupleDelimiterTok(left, is_opening=True)) or
        (rval == '}' and
         _IsDictListTupleDelimiterTok(right, is_opening=False)))):
      return True
    if (style.GetOrDefault('SPACES_AROUND_LIST_DELIMITERS', False) and (
        (lval == '[' and _IsDictListTupleDelimiterTok(left, is_opening=True)) or
        (rval == ']' and
         _IsDictListTupleDelimiterTok(right, is_opening=False)))):
      return True
    if (style.GetOrDefault('SPACES_AROUND_TUPLE_DELIMITERS', False) and (
        (lval == '(' and _IsDictListTupleDelimiterTok(left, is_opening=True)) or
        (rval == ')' and
         _IsDictListTupleDelimiterTok(right, is_opening=False)))):
      return True
  if left.OpensScope() and right.OpensScope():
    # Nested objects' opening brackets shouldn't be separated, unless enabled
    # by SPACE_INSIDE_BRACKETS.
    return style.Get('SPACE_INSIDE_BRACKETS')
  if left.ClosesScope() and right.ClosesScope():
    # Nested objects' closing brackets shouldn't be separated, unless enabled
    # by SPACE_INSIDE_BRACKETS.
    return style.Get('SPACE_INSIDE_BRACKETS')
  if left.ClosesScope() and rval in '([':
    # A call, set, dictionary, or subscript that has a call or subscript after
    # it shouldn't have a space between them.
    return False
  if left.OpensScope() and _IsIdNumberStringToken(right):
    # Don't separate the opening bracket from the first item, unless enabled
    # by SPACE_INSIDE_BRACKETS.
    return style.Get('SPACE_INSIDE_BRACKETS')
  if left.is_name and rval in '([':
    # Don't separate a call or array access from the name.
    return False
  if right.ClosesScope():
    # Don't separate the closing bracket from the last item, unless enabled
    # by SPACE_INSIDE_BRACKETS.
    # FIXME(morbo): This might be too permissive.
    return style.Get('SPACE_INSIDE_BRACKETS')
  if lval == 'print' and rval == '(':
    # Special support for the 'print' function.
    return False
  if left.OpensScope() and _IsUnaryOperator(right):
    # Don't separate a unary operator from the opening bracket, unless enabled
    # by SPACE_INSIDE_BRACKETS.
    return style.Get('SPACE_INSIDE_BRACKETS')
  if (left.OpensScope() and (subtypes.VARARGS_STAR in right.subtypes or
                             subtypes.KWARGS_STAR_STAR in right.subtypes)):
    # Don't separate a '*' or '**' from the opening bracket, unless enabled
    # by SPACE_INSIDE_BRACKETS.
    return style.Get('SPACE_INSIDE_BRACKETS')
  if rval == ';':
    # Avoid spaces before a semicolon. (Why is there a semicolon?!)
    return False
  if lval == '(' and rval == 'await':
    # Special support for the 'await' keyword. Don't separate the 'await'
    # keyword from an opening paren, unless enabled by SPACE_INSIDE_BRACKETS.
    return style.Get('SPACE_INSIDE_BRACKETS')
  return True


def _MustBreakBefore(prev_token, cur_token):
  """Return True if a line break is required before the current token."""
  if prev_token.is_comment or (prev_token.previous_token and
                               prev_token.is_pseudo and
                               prev_token.previous_token.is_comment):
    # Must break if the previous token was a comment.
    return True
  if (cur_token.is_string and prev_token.is_string and
      IsSurroundedByBrackets(cur_token)):
    # We want consecutive strings to be on separate lines. This is a
    # reasonable assumption, because otherwise they should have written them
    # all on the same line, or with a '+'.
    return True
  return cur_token.must_break_before


def _CanBreakBefore(prev_token, cur_token):
  """Return True if a line break may occur before the current token."""
  pval = prev_token.value
  cval = cur_token.value
  if pval == 'yield' and cval == 'from':
    # Don't break before a yield argument.
    return False
  if pval in {'async', 'await'} and cval in {'def', 'with', 'for'}:
    # Don't break after sync keywords.
    return False
  if cur_token.split_penalty >= split_penalty.UNBREAKABLE:
    return False
  if pval == '@':
    # Don't break right after the beginning of a decorator.
    return False
  if cval == ':':
    # Don't break before the start of a block of code.
    return False
  if cval == ',':
    # Don't break before a comma.
    return False
  if prev_token.is_name and cval == '(':
    # Don't break in the middle of a function definition or call.
    return False
  if prev_token.is_name and cval == '[':
    # Don't break in the middle of an array dereference.
    return False
  if cur_token.is_comment and prev_token.lineno == cur_token.lineno:
    # Don't break a comment at the end of the line.
    return False
  if subtypes.UNARY_OPERATOR in prev_token.subtypes:
    # Don't break after a unary token.
    return False
  if not style.Get('ALLOW_SPLIT_BEFORE_DEFAULT_OR_NAMED_ASSIGNS'):
    if (subtypes.DEFAULT_OR_NAMED_ASSIGN in cur_token.subtypes or
        subtypes.DEFAULT_OR_NAMED_ASSIGN in prev_token.subtypes):
      return False
  return True


def IsSurroundedByBrackets(tok):
  """Return True if the token is surrounded by brackets."""
  paren_count = 0
  brace_count = 0
  sq_bracket_count = 0
  previous_token = tok.previous_token
  while previous_token:
    if previous_token.value == ')':
      paren_count -= 1
    elif previous_token.value == '}':
      brace_count -= 1
    elif previous_token.value == ']':
      sq_bracket_count -= 1

    if previous_token.value == '(':
      if paren_count == 0:
        return previous_token
      paren_count += 1
    elif previous_token.value == '{':
      if brace_count == 0:
        return previous_token
      brace_count += 1
    elif previous_token.value == '[':
      if sq_bracket_count == 0:
        return previous_token
      sq_bracket_count += 1

    previous_token = previous_token.previous_token
  return None


def _IsDictListTupleDelimiterTok(tok, is_opening):
  assert tok

  if tok.matching_bracket is None:
    return False

  if is_opening:
    open_tok = tok
    close_tok = tok.matching_bracket
  else:
    open_tok = tok.matching_bracket
    close_tok = tok

  # There must be something in between the tokens
  if open_tok.next_token == close_tok:
    return False

  assert open_tok.next_token.node
  assert open_tok.next_token.node.parent

  return open_tok.next_token.node.parent.type in [
      python_symbols.dictsetmaker,
      python_symbols.listmaker,
      python_symbols.testlist_gexp,
  ]


_LOGICAL_OPERATORS = frozenset({'and', 'or'})
_BITWISE_OPERATORS = frozenset({'&', '|', '^'})
_ARITHMETIC_OPERATORS = frozenset({'+', '-', '*', '/', '%', '//', '@'})


def _SplitPenalty(prev_token, cur_token):
  """Return the penalty for breaking the line before the current token."""
  pval = prev_token.value
  cval = cur_token.value
  if pval == 'not':
    return split_penalty.UNBREAKABLE

  node_split_penalty = cur_token.node_split_penalty

  logical_splitting = style.Get('SPLIT_ALL_LOGICAL_OPERATORS_IF_ANY_SPLIT')

  if logical_splitting:
    if style.Get('SPLIT_BEFORE_LOGICAL_OPERATOR'):
      # Prefer to split before 'and' and 'or'.
      if pval in _LOGICAL_OPERATORS:
        return max(node_split_penalty,
                   style.Get('SPLIT_PENALTY_LOGICAL_OPERATOR'))
      if cval in _LOGICAL_OPERATORS:
        return max(node_split_penalty, 0)
    else:
      # Prefer to split after 'and' and 'or'.
      if pval in _LOGICAL_OPERATORS:
        return max(node_split_penalty, 0)
      if cval in _LOGICAL_OPERATORS:
        return max(node_split_penalty,
                   style.Get('SPLIT_PENALTY_LOGICAL_OPERATOR'))

  if node_split_penalty > 0:
    return node_split_penalty

  if not logical_splitting:
    if style.Get('SPLIT_BEFORE_LOGICAL_OPERATOR'):
      # Prefer to split before 'and' and 'or'.
      if pval in _LOGICAL_OPERATORS:
        return style.Get('SPLIT_PENALTY_LOGICAL_OPERATOR')
      if cval in _LOGICAL_OPERATORS:
        return 0
    else:
      # Prefer to split after 'and' and 'or'.
      if pval in _LOGICAL_OPERATORS:
        return 0
      if cval in _LOGICAL_OPERATORS:
        return style.Get('SPLIT_PENALTY_LOGICAL_OPERATOR')

  if style.Get('SPLIT_BEFORE_BITWISE_OPERATOR'):
    # Prefer to split before '&', '|', and '^'.
    if pval in _BITWISE_OPERATORS:
      return style.Get('SPLIT_PENALTY_BITWISE_OPERATOR')
    if cval in _BITWISE_OPERATORS:
      return 0
  else:
    # Prefer to split after '&', '|', and '^'.
    if pval in _BITWISE_OPERATORS:
      return 0
    if cval in _BITWISE_OPERATORS:
      return style.Get('SPLIT_PENALTY_BITWISE_OPERATOR')

  if (subtypes.COMP_FOR in cur_token.subtypes or
      subtypes.COMP_IF in cur_token.subtypes):
    # We don't mind breaking before the 'for' or 'if' of a list comprehension.
    return 0
  if subtypes.UNARY_OPERATOR in prev_token.subtypes:
    # Try not to break after a unary operator.
    return style.Get('SPLIT_PENALTY_AFTER_UNARY_OPERATOR')
  if pval == ',':
    # Breaking after a comma is fine, if need be.
    return 0
  if pval == '**' or cval == '**':
    return split_penalty.STRONGLY_CONNECTED
  if (subtypes.VARARGS_STAR in prev_token.subtypes or
      subtypes.KWARGS_STAR_STAR in prev_token.subtypes):
    # Don't split after a varargs * or kwargs **.
    return split_penalty.UNBREAKABLE
  if prev_token.OpensScope() and cval != '(':
    # Slightly prefer
    return style.Get('SPLIT_PENALTY_AFTER_OPENING_BRACKET')
  if cval == ':':
    # Don't split before a colon.
    return split_penalty.UNBREAKABLE
  if cval == '=':
    # Don't split before an assignment.
    return split_penalty.UNBREAKABLE
  if (subtypes.DEFAULT_OR_NAMED_ASSIGN in prev_token.subtypes or
      subtypes.DEFAULT_OR_NAMED_ASSIGN in cur_token.subtypes):
    # Don't break before or after an default or named assignment.
    return split_penalty.UNBREAKABLE
  if cval == '==':
    # We would rather not split before an equality operator.
    return split_penalty.STRONGLY_CONNECTED
  if cur_token.ClosesScope():
    # Give a slight penalty for splitting before the closing scope.
    return 100
  return 0