PhpCsFixer\Tokenizer\Tokens::getPrevNonWhitespace PHP Method

    public function getPrevNonWhitespace($index, $whitespaces = null)
    {
        return $this->getNonWhitespaceSibling($index, -1, $whitespaces);
    }

 /**
  * {@inheritdoc}
  */
 public function fix(\SplFileInfo $file, Tokens $tokens)
 {
     for ($index = $tokens->count() - 1; $index >= 0; --$index) {
         $token = $tokens[$index];
         if (!$token->isGivenKind(T_FUNCTION)) {
             continue;
         }
         $startParenthesisIndex = $tokens->getNextTokenOfKind($index, array('('));
         $endParenthesisIndex = $tokens->findBlockEnd(Tokens::BLOCK_TYPE_PARENTHESIS_BRACE, $startParenthesisIndex);
         for ($iter = $endParenthesisIndex - 1; $iter > $startParenthesisIndex; --$iter) {
             if (!$tokens[$iter]->isGivenKind(T_VARIABLE)) {
                 continue;
             }
             // skip ... before $variable for variadic parameter
             if (defined('T_ELLIPSIS')) {
                 $prevNonWhitespaceIndex = $tokens->getPrevNonWhitespace($iter);
                 if ($tokens[$prevNonWhitespaceIndex]->isGivenKind(T_ELLIPSIS)) {
                     $iter = $prevNonWhitespaceIndex;
                 }
             }
             // skip & before $variable for parameter passed by reference
             $prevNonWhitespaceIndex = $tokens->getPrevNonWhitespace($iter);
             if ($tokens[$prevNonWhitespaceIndex]->equals('&')) {
                 $iter = $prevNonWhitespaceIndex;
             }
             if (!$tokens[$iter - 1]->equalsAny(array(array(T_WHITESPACE), array(T_COMMENT), array(T_DOC_COMMENT), '(', ','))) {
                 $tokens->insertAt($iter, new Token(array(T_WHITESPACE, ' ')));
             }
         }
     }
 }