def CheckToken(self, token, state):

    # Call the base class's CheckToken function.
    super(JavaScriptLintRules, self).CheckToken(token, state)

    # Store some convenience variables
    namespaces_info = self._namespaces_info

    if error_check.ShouldCheck(Rule.UNUSED_LOCAL_VARIABLES):
      self._CheckUnusedLocalVariables(token, state)

    if error_check.ShouldCheck(Rule.UNUSED_PRIVATE_MEMBERS):
      # Find all assignments to private members.
      if token.type == Type.SIMPLE_LVALUE:
        identifier = token.string
        if identifier.endswith('_') and not identifier.endswith('__'):
          doc_comment = state.GetDocComment()
          suppressed = doc_comment and (
              'underscore' in doc_comment.suppressions or
              'unusedPrivateMembers' in doc_comment.suppressions)
          if not suppressed:
            # Look for static members defined on a provided namespace.
            if namespaces_info:
              namespace = namespaces_info.GetClosurizedNamespace(identifier)
              provided_namespaces = namespaces_info.GetProvidedNamespaces()
            else:
              namespace = None
              provided_namespaces = set()

            # Skip cases of this.something_.somethingElse_.
            regex = re.compile(r'^this\.[a-zA-Z_]+$')
            if namespace in provided_namespaces or regex.match(identifier):
              variable = identifier.split('.')[-1]
              self._declared_private_member_tokens[variable] = token
              self._declared_private_members.add(variable)
        elif not identifier.endswith('__'):
          # Consider setting public members of private members to be a usage.
          for piece in identifier.split('.'):
            if piece.endswith('_'):
              self._used_private_members.add(piece)

      # Find all usages of private members.
      if token.type == Type.IDENTIFIER:
        for piece in token.string.split('.'):
          if piece.endswith('_'):
            self._used_private_members.add(piece)

    if token.type == Type.DOC_FLAG:
      flag = token.attached_object

      if flag.flag_type == 'param' and flag.name_token is not None:
        self._CheckForMissingSpaceBeforeToken(
            token.attached_object.name_token)

        if flag.type is not None and flag.name is not None:
          if error_check.ShouldCheck(Rule.VARIABLE_ARG_MARKER):
            # Check for variable arguments marker in type.
            if flag.jstype.IsVarArgsType() and flag.name != 'var_args':
              self._HandleError(errors.JSDOC_MISSING_VAR_ARGS_NAME,
                                'Variable length argument %s must be renamed '
                                'to var_args.' % flag.name,
                                token)
            elif not flag.jstype.IsVarArgsType() and flag.name == 'var_args':
              self._HandleError(errors.JSDOC_MISSING_VAR_ARGS_TYPE,
                                'Variable length argument %s type must start '
                                'with \'...\'.' % flag.name,
                                token)

          if error_check.ShouldCheck(Rule.OPTIONAL_TYPE_MARKER):
            # Check for optional marker in type.
            if (flag.jstype.opt_arg and
                not flag.name.startswith('opt_')):
              self._HandleError(errors.JSDOC_MISSING_OPTIONAL_PREFIX,
                                'Optional parameter name %s must be prefixed '
                                'with opt_.' % flag.name,
                                token)
            elif (not flag.jstype.opt_arg and
                  flag.name.startswith('opt_')):
              self._HandleError(errors.JSDOC_MISSING_OPTIONAL_TYPE,
                                'Optional parameter %s type must end with =.' %
                                flag.name,
                                token)

      if flag.flag_type in state.GetDocFlag().HAS_TYPE:
        # Check for both missing type token and empty type braces '{}'
        # Missing suppress types are reported separately and we allow enums,
        # const, private, public and protected without types.
        if (flag.flag_type not in state.GetDocFlag().CAN_OMIT_TYPE
            and (not flag.jstype or flag.jstype.IsEmpty())):
          self._HandleError(errors.MISSING_JSDOC_TAG_TYPE,
                            'Missing type in %s tag' % token.string, token)

        elif flag.name_token and flag.type_end_token and tokenutil.Compare(
            flag.type_end_token, flag.name_token) > 0:
          self._HandleError(
              errors.OUT_OF_ORDER_JSDOC_TAG_TYPE,
              'Type should be immediately after %s tag' % token.string,
              token)

    elif token.type == Type.DOUBLE_QUOTE_STRING_START:
      next_token = token.next
      while next_token.type == Type.STRING_TEXT:
        if javascripttokenizer.JavaScriptTokenizer.SINGLE_QUOTE.search(
            next_token.string):
          break
        next_token = next_token.next
      else:
        self._HandleError(
            errors.UNNECESSARY_DOUBLE_QUOTED_STRING,
            'Single-quoted string preferred over double-quoted string.',
            token,
            position=Position.All(token.string))

    elif token.type == Type.END_DOC_COMMENT:
      doc_comment = state.GetDocComment()

      # When @externs appears in a @fileoverview comment, it should trigger
      # the same limited doc checks as a special filename like externs.js.
      if doc_comment.HasFlag('fileoverview') and doc_comment.HasFlag('externs'):
        self._SetLimitedDocChecks(True)

      if (error_check.ShouldCheck(Rule.BLANK_LINES_AT_TOP_LEVEL) and
          not self._is_html and
          state.InTopLevel() and
          not state.InNonScopeBlock()):

        # Check if we're in a fileoverview or constructor JsDoc.
        is_constructor = (
            doc_comment.HasFlag('constructor') or
            doc_comment.HasFlag('interface'))
        # @fileoverview is an optional tag so if the dosctring is the first
        # token in the file treat it as a file level docstring.
        is_file_level_comment = (
            doc_comment.HasFlag('fileoverview') or
            not doc_comment.start_token.previous)

        # If the comment is not a file overview, and it does not immediately
        # precede some code, skip it.
        # NOTE: The tokenutil methods are not used here because of their
        # behavior at the top of a file.
        next_token = token.next
        if (not next_token or
            (not is_file_level_comment and
             next_token.type in Type.NON_CODE_TYPES)):
          return

        # Don't require extra blank lines around suppression of extra
        # goog.require errors.
        if (doc_comment.SuppressionOnly() and
            next_token.type == Type.IDENTIFIER and
            next_token.string in ['goog.provide', 'goog.require']):
          return

        # Find the start of this block (include comments above the block, unless
        # this is a file overview).
        block_start = doc_comment.start_token
        if not is_file_level_comment:
          token = block_start.previous
          while token and token.type in Type.COMMENT_TYPES:
            block_start = token
            token = token.previous

        # Count the number of blank lines before this block.
        blank_lines = 0
        token = block_start.previous
        while token and token.type in [Type.WHITESPACE, Type.BLANK_LINE]:
          if token.type == Type.BLANK_LINE:
            # A blank line.
            blank_lines += 1
          elif token.type == Type.WHITESPACE and not token.line.strip():
            # A line with only whitespace on it.
            blank_lines += 1
          token = token.previous

        # Log errors.
        error_message = False
        expected_blank_lines = 0

        # Only need blank line before file overview if it is not the beginning
        # of the file, e.g. copyright is first.
        if is_file_level_comment and blank_lines == 0 and block_start.previous:
          error_message = 'Should have a blank line before a file overview.'
          expected_blank_lines = 1
        elif is_constructor and blank_lines != 3:
          error_message = (
              'Should have 3 blank lines before a constructor/interface.')
          expected_blank_lines = 3
        elif (not is_file_level_comment and not is_constructor and
              blank_lines != 2):
          error_message = 'Should have 2 blank lines between top-level blocks.'
          expected_blank_lines = 2

        if error_message:
          self._HandleError(
              errors.WRONG_BLANK_LINE_COUNT, error_message,
              block_start, position=Position.AtBeginning(),
              fix_data=expected_blank_lines - blank_lines)

    elif token.type == Type.END_BLOCK:
      if state.InFunction() and state.IsFunctionClose():
        is_immediately_called = (token.next and
                                 token.next.type == Type.START_PAREN)

        function = state.GetFunction()
        if not self._limited_doc_checks:
          if (function.has_return and function.doc and
              not is_immediately_called and
              not function.doc.HasFlag('return') and
              not function.doc.InheritsDocumentation() and
              not function.doc.HasFlag('constructor')):
            # Check for proper documentation of return value.
            self._HandleError(
                errors.MISSING_RETURN_DOCUMENTATION,
                'Missing @return JsDoc in function with non-trivial return',
                function.doc.end_token, position=Position.AtBeginning())
          elif (not function.has_return and
                not function.has_throw and
                function.doc and
                function.doc.HasFlag('return') and
                not state.InInterfaceMethod()):
            flag = function.doc.GetFlag('return')
            valid_no_return_names = ['undefined', 'void', '*']
            invalid_return = flag.jstype is None or not any(
                sub_type.identifier in valid_no_return_names
                for sub_type in flag.jstype.IterTypeGroup())

            if invalid_return:
              self._HandleError(
                  errors.UNNECESSARY_RETURN_DOCUMENTATION,
                  'Found @return JsDoc on function that returns nothing',
                  flag.flag_token, position=Position.AtBeginning())

        # b/4073735. Method in object literal definition of prototype can
        # safely reference 'this'.
        prototype_object_literal = False
        block_start = None
        previous_code = None
        previous_previous_code = None

        # Search for cases where prototype is defined as object literal.
        #       previous_previous_code
        #       |       previous_code
        #       |       | block_start
        #       |       | |
        # a.b.prototype = {
        #   c : function() {
        #     this.d = 1;
        #   }
        # }

        # If in object literal, find first token of block so to find previous
        # tokens to check above condition.
        if state.InObjectLiteral():
          block_start = state.GetCurrentBlockStart()

        # If an object literal then get previous token (code type). For above
        # case it should be '='.
        if block_start:
          previous_code = tokenutil.SearchExcept(block_start,
                                                 Type.NON_CODE_TYPES,
                                                 reverse=True)

        # If previous token to block is '=' then get its previous token.
        if previous_code and previous_code.IsOperator('='):
          previous_previous_code = tokenutil.SearchExcept(previous_code,
                                                          Type.NON_CODE_TYPES,
                                                          reverse=True)

        # If variable/token before '=' ends with '.prototype' then its above
        # case of prototype defined with object literal.
        prototype_object_literal = (previous_previous_code and
                                    previous_previous_code.string.endswith(
                                        '.prototype'))

        if (function.has_this and function.doc and
            not function.doc.HasFlag('this') and
            not function.is_constructor and
            not function.is_interface and
            '.prototype.' not in function.name and
            not prototype_object_literal):
          self._HandleError(
              errors.MISSING_JSDOC_TAG_THIS,
              'Missing @this JsDoc in function referencing "this". ('
              'this usually means you are trying to reference "this" in '
              'a static function, or you have forgotten to mark a '
              'constructor with @constructor)',
              function.doc.end_token, position=Position.AtBeginning())

    elif token.type == Type.IDENTIFIER:
      if token.string == 'goog.inherits' and not state.InFunction():
        if state.GetLastNonSpaceToken().line_number == token.line_number:
          self._HandleError(
              errors.MISSING_LINE,
              'Missing newline between constructor and goog.inherits',
              token,
              position=Position.AtBeginning())

        extra_space = state.GetLastNonSpaceToken().next
        while extra_space != token:
          if extra_space.type == Type.BLANK_LINE:
            self._HandleError(
                errors.EXTRA_LINE,
                'Extra line between constructor and goog.inherits',
                extra_space)
          extra_space = extra_space.next

        # TODO(robbyw): Test the last function was a constructor.
        # TODO(robbyw): Test correct @extends and @implements documentation.

      elif (token.string == 'goog.provide' and
            not state.InFunction() and
            namespaces_info is not None):
        namespace = tokenutil.GetStringAfterToken(token)

        # Report extra goog.provide statement.
        if not namespace or namespaces_info.IsExtraProvide(token):
          if not namespace:
            msg = 'Empty namespace in goog.provide'
          else:
            msg = 'Unnecessary goog.provide: ' +  namespace

            # Hint to user if this is a Test namespace.
            if namespace.endswith('Test'):
              msg += (' *Test namespaces must be mentioned in the '
                      'goog.setTestOnly() call')

          self._HandleError(
              errors.EXTRA_GOOG_PROVIDE,
              msg,
              token, position=Position.AtBeginning())

        if namespaces_info.IsLastProvide(token):
          # Report missing provide statements after the last existing provide.
          missing_provides = namespaces_info.GetMissingProvides()
          if missing_provides:
            self._ReportMissingProvides(
                missing_provides,
                tokenutil.GetLastTokenInSameLine(token).next,
                False)

          # If there are no require statements, missing requires should be
          # reported after the last provide.
          if not namespaces_info.GetRequiredNamespaces():
            missing_requires, illegal_alias_statements = (
                namespaces_info.GetMissingRequires())
            if missing_requires:
              self._ReportMissingRequires(
                  missing_requires,
                  tokenutil.GetLastTokenInSameLine(token).next,
                  True)
            if illegal_alias_statements:
              self._ReportIllegalAliasStatement(illegal_alias_statements)

      elif (token.string == 'goog.require' and
            not state.InFunction() and
            namespaces_info is not None):
        namespace = tokenutil.GetStringAfterToken(token)

        # If there are no provide statements, missing provides should be
        # reported before the first require.
        if (namespaces_info.IsFirstRequire(token) and
            not namespaces_info.GetProvidedNamespaces()):
          missing_provides = namespaces_info.GetMissingProvides()
          if missing_provides:
            self._ReportMissingProvides(
                missing_provides,
                tokenutil.GetFirstTokenInSameLine(token),
                True)

        # Report extra goog.require statement.
        if not namespace or namespaces_info.IsExtraRequire(token):
          if not namespace:
            msg = 'Empty namespace in goog.require'
          else:
            msg = 'Unnecessary goog.require: ' + namespace

          self._HandleError(
              errors.EXTRA_GOOG_REQUIRE,
              msg,
              token, position=Position.AtBeginning())

        # Report missing goog.require statements.
        if namespaces_info.IsLastRequire(token):
          missing_requires, illegal_alias_statements = (
              namespaces_info.GetMissingRequires())
          if missing_requires:
            self._ReportMissingRequires(
                missing_requires,
                tokenutil.GetLastTokenInSameLine(token).next,
                False)
          if illegal_alias_statements:
            self._ReportIllegalAliasStatement(illegal_alias_statements)

    elif token.type == Type.OPERATOR:
      last_in_line = token.IsLastInLine()
      # If the token is unary and appears to be used in a unary context
      # it's ok.  Otherwise, if it's at the end of the line or immediately
      # before a comment, it's ok.
      # Don't report an error before a start bracket - it will be reported
      # by that token's space checks.
      if (not token.metadata.IsUnaryOperator() and not last_in_line
          and not token.next.IsComment()
          and not token.next.IsOperator(',')
          and not tokenutil.IsDot(token)
          and token.next.type not in (Type.WHITESPACE, Type.END_PAREN,
                                      Type.END_BRACKET, Type.SEMICOLON,
                                      Type.START_BRACKET)):
        self._HandleError(
            errors.MISSING_SPACE,
            'Missing space after "%s"' % token.string,
            token,
            position=Position.AtEnd(token.string))
    elif token.type == Type.WHITESPACE:
      first_in_line = token.IsFirstInLine()
      last_in_line = token.IsLastInLine()
      # Check whitespace length if it's not the first token of the line and
      # if it's not immediately before a comment.
      if not last_in_line and not first_in_line and not token.next.IsComment():
        # Ensure there is no space after opening parentheses.
        if (token.previous.type in (Type.START_PAREN, Type.START_BRACKET,
                                    Type.FUNCTION_NAME)
            or token.next.type == Type.START_PARAMETERS):
          self._HandleError(
              errors.EXTRA_SPACE,
              'Extra space after "%s"' % token.previous.string,
              token,
              position=Position.All(token.string))
    elif token.type == Type.SEMICOLON:
      previous_token = tokenutil.SearchExcept(token, Type.NON_CODE_TYPES,
                                              reverse=True)
      if not previous_token:
        self._HandleError(
            errors.REDUNDANT_SEMICOLON,
            'Semicolon without any statement',
            token,
            position=Position.AtEnd(token.string))
      elif (previous_token.type == Type.KEYWORD and
            previous_token.string not in ['break', 'continue', 'return']):
        self._HandleError(
            errors.REDUNDANT_SEMICOLON,
            ('Semicolon after \'%s\' without any statement.'
             ' Looks like an error.' % previous_token.string),
            token,
            position=Position.AtEnd(token.string))
Checks a token, given the current parser_state, for warnings and errors.
dataset/ETHPy150Open google/closure-linter/closure_linter/javascriptlintrules.py/JavaScriptLintRules.CheckToken