Misago/misago/categories/urls/__init__.py

from django.urls import path

from ...conf import settings
from ...core.views import home_redirect

from ..views import categories

if settings.MISAGO_THREADS_ON_INDEX:
    URL_PATH = "categories/"
else:
    URL_PATH = ""

urlpatterns = [
    path(URL_PATH, categories, name="categories"),
    # fallback for after we changed index setting
    path("categories/", home_redirect),
]