code: private function fixSpace2(Tokens $tokens, $index)
      {
          // remove space before comma if exist
          if ($tokens[$index - 1]->isWhitespace()) {
              $prevIndex = $tokens->getPrevNonWhitespace($index - 1);
  
              if (!$tokens[$prevIndex]->equalsAny([',', [T_END_HEREDOC]]) && !$tokens[$prevIndex]->isComment()) {
                  $tokens->clearAt($index - 1);
              }
          }
  
          $nextIndex = $index + 1;
          $nextToken = $tokens[$nextIndex];
  
          // Two cases for fix space after comma (exclude multiline comments)
          //  1) multiple spaces after comma
          //  2) no space after comma
          if ($nextToken->isWhitespace()) {
              $newContent = $nextToken->getContent();
  
              if ('ensure_single_line' === $this->configuration['on_multiline']) {
                  $newContent = Preg::replace('/\R/', '', $newContent);
              }
  
              if (
                  (!$this->configuration['keep_multiple_spaces_after_comma'] || Preg::match('/\R/', $newContent))
                  && !$this->isCommentLastLineToken($tokens, $index + 2)
              ) {
                  $newContent = ltrim($newContent, " \t");
              }
  
              $tokens[$nextIndex] = new Token([T_WHITESPACE, '' === $newContent ? ' ' : $newContent]);
  
              return;
          }
  
          if (!$this->isCommentLastLineToken($tokens, $index + 1)) {
              $tokens->insertAt($index + 1, new Token([T_WHITESPACE, ' ']));
          }
      }
docs: Method to insert space after comma and remove space before comma.
  
  @param Tokens $tokens
  @param int    $index