for loop var should be available to contextfunction

[jpellerin]

Given a template like:

{% for a in [1, 2, 3] %}
{{ somefunc() }}
{% end for %}

And assuming somefunc() is a contextfunction, I expected 'a' to be available in somefunc()'s context, but it isn't. I find this very counter-intuitive.

The same is true of variables set inside of a for loop via {% set %}.

In both cases, instead of a locally-scoped context, or updating context.vars, jinja2 only creates local vars in the generated python code, which prevents contextfunctions and contextfilters from seeing them.

[jpellerin]

Draft implementation can be pulled from bitbucket here: https://bitbucket.org/jpellerin/jinja2-main

[mitsuhiko]

It is documented that the context is only used as a data source, not data store. This is impossible with the current architecture to get right, and changing that would make the whole template execution a lot slower.