Let Context handle include, extends and inclusion_tag template loading

[Johannes Dollinger]

• Add a loader kwarg to Context which should be something with a get_template(name) function. Default would be django.template.loader.
• Provide get_template() and select_template() methods on Context, use these in include, extends and inclusion_tag.
• Cache templates in Context, optionally: provide a way to populate this cache.
• Remove ConstantIncludeNode since caching would provide the same benefits and it causes problems with recursive includes.

This would fix

• #2949 - templating engine too tightly tied to TEMPLATE_DIRS in the settings
• #3544 - recursive includes
• #4278 - get_template should accept a dirs argument
• #6834 - support for templates to be loaded from dynamically-selected directories

Example:

class PrefixLoader:
    def __init__(self, prefix_list):
        self.prefix_list = prefix_list
    def get_template(name):
        from django.template.loader import select_template
        return select_template(['%s/%s' % (prefix, name) for prefix in self.prefix_list])

tpl.render(Context({}, loader=PrefixLoader(['a', 'b', 'c'])))

[Johannes Dollinger]

depends on tplrf.2.diff and tplrf-tests.diff from #7806

[Johannes Dollinger]

patch -p0 tplrf.2.diff
patch -p0 tplrf-tests.diff
patch -p1 7815.tplrf.diff

mostly done. contains a test for recursive includes, but no tests for the loader feature yet.

[Johannes Dollinger]

This would also fix #7931.

Forgot to mention in the ticket description: this is a backwards incompatible change. If you rely on compile time side effects (e.g. {% load %}) in included templates, that will break.

[(none)]

Milestone post-1.0 deleted

[Russell Keith-Magee]

The three (remaining) individual tickets (#3544, #4278, #6834) are all good ideas, but an omnibus patch makes it really hard to evaluate which bits are fixing what. It's also an area that needs a lot of cleanup following the 1.2 template loader changes.

Closing wontfix, mostly as a procedural thing; we'd prefer to see single patches for single issues, or a merging of issues into a single ticket (resulting in the previous tickets getting closed).