Allow template tags to set extra data on templates.

[Carlton Gibson]

Custom template tags may need to pass additional data, beyond the node list, out of the parsing context, for later use, by (e.g.) the template loader, or other template clients.

Currently this is only feasible by attaching data to the origin object, since that's the only object available to both the template and the parser, but this isn't pretty.

I propose adding an additional attribute to the Parser that can be used by template tag authors to have extra data set on the template instance, that can then be used as needed.

This ticket comes from the forum discussion on ​Adding template fragments or partials for the DTL — it is the necessary minimal first change to allow an official[*] API such that a library such as django-template-partials can pass named node lists out of the parser for later use. (I'd imagine it would be useful to other tag library authors once in play.)

[*]: I say official, but I'm not sure whether to make this public — i.e. documented — it's pretty niche — those who need it'll find it. I'd be happy with a regression test making sure it didn't break but leaving it undocumented beyond that. Opinions welcome. 🙂

[Carlton Gibson]

​PR

[Mariusz Felisiak]

Seems reasonable.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 35bbb2c:

Fixed #34883 -- Allowed template tags to set extra data on templates.

By setting a value in the parser.extra_data mapping, template tags
pass additional data out of the parsing context.

Any extra data set is exposed on the template via the matching
.extra_data attribute.

Library authors should use a key to namespace extra data. The 'django'
namespace is reserved for internal use.