code: protected function linkFrameworkAndExtensions($dir, $base)
      {
          if (is_dir($link = "$dir/vendor/yiisoft/yii2")) {
              $this->stdout("Removing dir $link.\n");
              FileHelper::removeDirectory($link);
              $this->stdout("Creating symlink for $link.\n");
              symlink("$base/framework", $link);
          }
          $extensions = $this->findDirs("$dir/vendor/yiisoft");
          foreach ($extensions as $ext) {
              if (is_dir($link = "$dir/vendor/yiisoft/yii2-$ext")) {
                  $this->stdout("Removing dir $link.\n");
                  FileHelper::removeDirectory($link);
                  $this->stdout("Creating symlink for $link.\n");
                  if (!file_exists("$base/extensions/$ext")) {
                      $ret = $this->actionExt($ext);
                      if ($ret !== 0) {
                          return $ret;
                      }
                  }
                  symlink("$base/extensions/$ext", $link);
              }
          }
      }
docs: Creates symlinks to framework and extension sources for the application.
  @param string $dir application directory
  @param string $base Yii sources base directory
  
  @return int