Interaction with Context OG

As far as I can tell, there is a very nasty cache bug in og_context() that sometimes causes the page to be cached with the wrong theme.

This admittedly ugly patch works around the problem by invalidating the page cache until og_context() sends a proper value.

In my case, I've tracked this down to a problem in entity_cache. If the parent group node is not in {cache_entity_node}, the lookup sometimes fails.

I wonder if this is a problem with entity_metadata_wrapper().

That's not it. But on cache clear, menu_get_custom_theme() is returning NULL.

After thorough research, I don't think this is a context issue. It looks like a race condition in core.

See #943616: hook_custom_theme() does not work as expected and #1120188: Default Theme intermittently replaces Sub Theme for information about the reasons.

I ended up writing a custom hook_init() to force the theme to reset. I don't think that approach is appropriate for a patch to OG Theme. Though it could be moved to og_theme_init().

/**
 * Implements hook_init().
 */
function custom_init() {
  // This is a very nasty hack around https://drupal.org/node/1120188 and
  // https://drupal.org/node/943616.
  // FORCE the theme to re-initialize.
  unset($GLOBALS['theme']);
  drupal_theme_initialize();
}

That approach has issues with subthemes and admin pages, so I wrote a more robust version.

/**
 * Implements hook_init().
 */
function custom_init() {
  global $user;
  // This is a very nasty hack around https://drupal.org/node/1120188 and
  // https://drupal.org/node/943616.
  // FORCE the theme to re-initialize.
  if ($admin = path_is_admin(current_path())) {
    return;
  }

  // Only run if the page has not been cached.
  // This is a minor performance hit for authenticated users.
  $page_cache = cache_get(current_path(), 'cache_page');
  if (!$user->uid && $page_cache) {
    return;
  }

  // Reset loaded CSS, because sub-themes already ran.
  drupal_static_reset('drupal_add_css');

  // Reload the theme.
  unset($GLOBALS['theme']);
  drupal_theme_initialize();
}

Although this issue is closed, we had the same problem with a different workaround that I thought was worth sharing for anyone that finds the issue in the future.

Our approach was to avoid using og_context if it was possible to find the group type and ID from arg(). This only works for groups that are nodes but I'm sure it could be easily modified for other entities if required. It falls back to og_context if the shortcut doesn't work but

Again, as agentrickard has said, this is very much a workaround and I wouldn't expect it to be committed to the module unless a generic version could be made.