fillInSubThemeData example

$sub_themes[] = $name;
      }
      // Add status.       $theme->status = (int) isset($this->installedThemes[$name]);
    }

    // Build dependencies.     $themes = $this->moduleHandler->buildModuleDependencies($themes);

    // After establishing the full list of available themes, fill in data for     // sub-themes.     $this->fillInSubThemeData($themes, $sub_themes);

    foreach ($themes as $theme) {
      // After $theme is processed by buildModuleDependencies(), there can be a       // `$theme->requires` array containing both module and base theme       // dependencies. The module dependencies are copied to their own property       // so they are available to operations specific to module dependencies.       if (isset($theme->requires)) {
        $theme->module_dependencies = array_diff_key($theme->requires, $themes);
      }
      else {
        // Even if no requirements are specified, the theme installation process