Refs #7261 -- Made strings escaped by Django usable in third-party libs.
The changes in mark_safe and mark_for_escaping are straightforward. The
more tricky part is to handle correctly objects that implement __html__.
Historically escape() has escaped SafeData. Even if that doesn't seem a
good behavior, changing it would create security concerns. Therefore
support for __html__() was only added to conditional_escape() where this
concern doesn't exist.
Then using conditional_escape() instead of escape() in the Django
template engine makes it understand data escaped by other libraries.
Template filter |escape accounts for __html__() when it's available.
|force_escape forces the use of Django's HTML escaping implementation.
Here's why the change in render_value_in_context() is safe. Before Django
1.7 conditional_escape() was implemented as follows:
if isinstance(text, SafeData):
return text
else:
return escape(text)
render_value_in_context() never called escape() on SafeData. Therefore
replacing escape() with conditional_escape() doesn't change the
autoescaping logic as it was originally intended.
This change should be backported to Django 1.7 because it corrects a
feature added in Django 1.7.
Thanks mitsuhiko for the report.
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