protected function loadResourcesFromTheme(string $cacheKey, &$theme)
    {
        if (!$theme instanceof \Twig_Template) {
            /* @var \Twig_Template $theme */
            $theme = $this->environment->loadTemplate($theme);
        }

        if (null === $this->template) {
            // Store the first \Twig_Template instance that we find so that
            // we can call displayBlock() later on. It doesn't matter *which*
            // template we use for that, since we pass the used blocks manually
            // anyway.
            $this->template = $theme;
        }

        // Use a separate variable for the inheritance traversal, because
        // theme is a reference and we don't want to change it.
        $currentTheme = $theme;

        $context = $this->environment->mergeGlobals([]);

        // The do loop takes care of template inheritance.
        // Add blocks from all templates in the inheritance tree, but avoid
        // overriding blocks already set.
        do {
            foreach ($currentTheme->getBlocks() as $block => $blockData) {
                if (!isset($this->resources[$cacheKey][$block])) {
                    // The resource given back is the key to the bucket that
                    // contains this block.
                    $this->resources[$cacheKey][$block] = $blockData;
                }
            }
        } while (false !== $currentTheme = $currentTheme->getParent($context));
    }