Re: [Django] #34692: django.forms.renderers.get_default_renderer()'s template loader cache is not being reset on autoloads. (was: django.forms.get_default_renderer()'s template loader cache is not being reset on autoloads.)

[Django]

#34692: django.forms.renderers.get_default_renderer()'s template loader cache is
not being reset on autoloads.
-------------------------------+--------------------------------------
Reporter: kukwaa | Owner: nobody
Type: Bug | Status: new
Component: Uncategorized | Version: 4.2
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------+--------------------------------------
Description changed by kukwaa:

Old description:

> 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()
> }}}

New description:

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 crude 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()
}}}

--

--
Ticket URL: <https://code.djangoproject.com/ticket/34692#comment:1>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.