entry-directories.c: Monitor mimeinfo.cache file and re-attempt

failed .desktop files when it changes (which is usually just after
the .desktop file is added, causing loading to fail due to
unavailable GAppInfo).  See inline comments.

Author: mtwebster

libmenu/entry-directories.c

@@ -57,6 +57,7 @@ struct CachedDir
 
   GSList *entries;
   GSList *subdirs;
+  GSList *retry_later_desktop_entries;
 
   MenuMonitor *dir_monitor;
   GSList      *monitors;
@@ -161,6 +162,9 @@ cached_dir_free (CachedDir *dir)
   g_slist_free (dir->subdirs);
   dir->subdirs = NULL;
 
+  g_slist_free_full (dir->retry_later_desktop_entries, g_free);
+  dir->retry_later_desktop_entries = NULL;
+
   g_free (dir->name);
   g_free (dir);
 }
@@ -317,7 +321,12 @@ cached_dir_add_entry (CachedDir  *dir,
 
   entry = desktop_entry_new (path);
   if (entry == NULL)
-    return FALSE;
+    {
+      menu_verbose ("Adding %s to the retry list (mimeinfo.cache maybe isn't done getting updated yet\n", path);
+
+      dir->retry_later_desktop_entries = g_slist_prepend (dir->retry_later_desktop_entries, g_strdup (path));
+      return FALSE;
+    }
 
   dir->entries = g_slist_prepend (dir->entries, entry);
 
@@ -525,6 +534,8 @@ handle_cached_dir_changed (MenuMonitor      *monitor,
                            CachedDir        *dir)
 {
   gboolean  handled = FALSE;
+  gboolean  retry_changes = FALSE;
+
   char     *basename;
   char     *dirname;
 
@@ -558,6 +569,58 @@ handle_cached_dir_changed (MenuMonitor      *monitor,
           break;
         }
     }
+  else if (g_strcmp0 (basename, "mimeinfo.cache") == 0)
+    {
+        /* The observed file notifies when a new desktop file is added
+         * (but fails to load) go something like:
+         *
+         * NOTIFY: foo.desktop
+         * NOTIFY: mimeinfo.cache.tempfile
+         * NOTIFY: mimeinfo.cache.tempfile
+         * NOTIFY: mimeinfo.cache
+         *
+         * Additionally, the failure is not upon trying to read the file,
+         * but attempting to get its GAppInfo (g_desktop_app_info_new_from_filename()
+         * in desktop-entries.c ln 277).  If you jigger desktop_entry_load() around 
+         * and read the file as a keyfile *first*, it succeeds.  If you then try
+         * to run g_desktop_app_info_new_from_keyfile(), *then* it fails.
+         *
+         * The theory here is there is a race condition where app info (which includes
+         * mimetype stuff) is unavailable because mimeinfo.cache is updated immediately
+         * after the app is installed.
+         *
+         * What we do here is, when a desktop fails to load, we add it to a temporary
+         * list.  We wait until mimeinfo.cache changes, then retry that desktop file,
+         * which succeeds this second time.
+         *
+         * Note: An alternative fix (presented more as a proof than a suggestion) is to
+         * change line 151 in menu-monitor.c to use g_timeout_add_seconds, and delay
+         * for one second.  This also avoids the issue (but it remains a race condition).
+         */
+
+        GSList *iter;
+
+        menu_verbose ("mimeinfo changed, checking for failed entries\n");
+
+        for (iter = dir->retry_later_desktop_entries; iter != NULL; iter = iter->next)
+          {
+            const gchar *retry_path = iter->data;
+
+            menu_verbose ("retrying %s\n", retry_path);
+
+            char *retry_basename = g_path_get_basename (retry_path);
+
+            if (cached_dir_update_entry (dir, retry_basename, retry_path))
+              retry_changes = TRUE;
+
+            g_free (retry_basename);
+          }
+
+        g_slist_free_full (dir->retry_later_desktop_entries, g_free);
+        dir->retry_later_desktop_entries = NULL;
+
+        handled = retry_changes;
+    }
   else /* Try recursing */
     {
       switch (event)
@@ -584,8 +647,8 @@ handle_cached_dir_changed (MenuMonitor      *monitor,
 
   if (handled)
     {
-      /* CHANGED events don't change the set of desktop entries */
-      if (event == MENU_MONITOR_EVENT_CREATED || event == MENU_MONITOR_EVENT_DELETED)
+      /* CHANGED events don't change the set of desktop entries, unless it's the mimeinfo.cache file changing */
+      if (retry_changes || (event == MENU_MONITOR_EVENT_CREATED || event == MENU_MONITOR_EVENT_DELETED))
         {
           _entry_directory_list_empty_desktop_cache ();
         }