Template libraries and built-ins should be registered through the engine

[Preston Timmons]

Django template libraries and builtins depend on global variables in django.template.base. This is messy, but also restrictive. The only way to specify template tag modules is by adding a package in INSTALLED_APPS that has a templatetags directory. Modifying builtins is a hack. And the LoadNode has a hard dependency on django.apps. Preferably, libraries and builtins should be specified and live on the Engine instance instead.

I think this can be cleaned up by having libraries and builtins configured via the DjangoTemplates backend. This would build on Mark Tamlyn's idea in #12772:

TEMPLATES = [
    {
        ...
        'OPTIONS': {
            'libraries': {
                'admin.urls': 'django.contrib.admin.templatetags.admin_urls',                  
                'my_tags': 'path.to.some.module',
            },
            'builtins': {
                'path.to.builtins_module',
            }
        },
    },
]

[Preston Timmons]

Hi akulokov,

I have a PR close to ready on this ticket. Just wanted to let you know since you assigned yourself, and I forgot to assign myself earlier.

[andrei kulakov]

@preston, no problem, unassigning myself..

[Tim Graham]

Should we close #17085 "Deprecate "add_to_builtins" and turn builtins into a property of Engine" as a duplicate?

[Preston Timmons <prestontimmons@…>]

In 655f5249:

Fixed #17085, #24783 -- Refactored template library registration.

• Converted the libraries and builtins globals of django.template.base into properties of the Engine class.
• Added a public API for explicit registration of libraries and builtins.