wgi/plugins.py: ignore empty plugin directories

Dynamic plugin registry returns as a plugin any folder within the
plugins directory. Web UI then attempts to load for each plugin 'foo' a
JavaScript file named 'foo/foo.js'. The problem is that if 'foo/foo.js'
does not exist, Web UI breaks and it is impossible to recover until the
empty folder is removed or 'foo/foo.js' (even empty) is created at the
server side.

Check that 'foo/foo.js' actual exists when including a plugin into the
registry.

Test the registry generator by creating fake plugins and removing them
during the test.

Fixes: https://pagure.io/freeipa/issue/8567

Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>

install/wsgi/plugins.py

@@ -36,7 +36,10 @@ def get_plugin_index():
 
     dirs = os.listdir(paths.IPA_JS_PLUGINS_DIR)
     index = 'define([],function(){return['
-    index += ','.join("'"+x+"'" for x in dirs)
+    for x in dirs:
+        p = os.path.join(paths.IPA_JS_PLUGINS_DIR, x, x + '.js')
+        if os.path.exists(p):
+            index += "'" + x + "',"
     index += '];});'
     return index.encode('utf-8')