code: public function isInstalled(InstalledRepositoryInterface $repo, PackageInterface $package)
      {
          if (!$repo->hasPackage($package)) {
              return false;
          }
  
          $installPath = $this->getInstallPath($package);
  
          if (is_readable($installPath)) {
              return true;
          }
  
          return (Platform::isWindows() && $this->filesystem->isJunction($installPath)) || is_link($installPath);
      }
docs: {@inheritDoc}