django.forms.get_default_renderer()'s template loader cache is not being reset on autoloads.

[Andrew]

Whenever a template file changes,
django.template.autoreload.template_changed() is called, which in turn calls
django.template.autoreload.reset_loaders(), which clears the template cache in every backend.engine's template loaders.

However, Django's renderer for Forms uses forms.renderers.get_default_renderer(), which returns a mixin that has its own engine instance, and therefore its own loaders (and template caches). This engine is never reset on autoloads. This means that any changes to a template that is referenced as part of, EG "Form.template_name", is never refreshed on changes. The entire runserver process must be restarted for any templates cached through forms.renders to be reloaded. This is tedious and does not match the behavior seen by non-form cached templates.

A simple fix can be demonstrated by changing reset_loaders() to the following:

def reset_loaders():
    for backend in engines.all():
        if not isinstance(backend, DjangoTemplates):
            continue
        for loader in backend.engine.template_loaders:
            loader.reset()

    # this code is new: reset the form renderer's template cache as well
    from django.forms.renderers import get_default_renderer
    for loader in get_default_renderer().engine.engine.template_loaders:
        loader.reset()