code: func (printer) isSingleLineList(l *ast.ListType) bool {
  	for _, item := range l.List {
  		if item.Pos().Line != l.Lbrack.Line {
  			return false
  		}
  
  		lit, ok := item.(*ast.LiteralType)
  		if !ok {
  			return false
  		}
  
  		if lit.Token.Type == token.HEREDOC && len(l.List) != 1 {
  			return false
  		}
  
  		if lit.LineComment != nil {
  			return false
  		}
  	}
  
  	return true
  }
docs: // isSingleLineList returns true if:
  // * they were previously formatted entirely on one line
  // * they consist entirely of literals
  // * there are either no heredoc strings or the list has exactly one element
  // * there are no line comments