drupal_find_theme_templates() assumes dynamic templates have 2 extensions

patch_commit_ad6b6cffcbbd.patch queued for re-testing.

I've recreated the patch for the current state of D8. The code seems fine, but I'm not entirely sure how to test that it does what is claims to do.

Considering this is now nearly three years old, is this still a valid issue?
Looking at that function now, it no longer resembles what the patch was against and processes the files in a different way:

        foreach ($matches as $match) {
          $file = $match;
          // Remove the extension from the filename.
          $file = str_replace($extension, '', $file);
          // Put the underscores back in for the hook name and register this
          // pattern.
          $arg_name = isset($info['variables']) ? 'variables' : 'render element';
          $implementations[strtr($file, '-', '_')] = array(
            'template' => $file,
            'path' => dirname($files[$match]->uri),
            $arg_name => $info[$arg_name],
            'base hook' => $hook,
          );
        }

I can confirm this was fixed in D8 by #1900458-13: Use .html.twig instead of .twig file extension, in particular see the interdiff there.

A similar approach should probably work fine for D7 because drupal_find_theme_templates() still gets an extension passed in. However, this change could be slightly risky. Changing the version accordingly so this can be considered, and bugs need tests.

Thanks for bumping this @oadaeh :)