[Django] #34578: Template filter `join` should not escape the joining string even if `autoescape` is `off`

[Django]

#34578: Template filter `join` should not escape the joining string even if
`autoescape` is `off`
-------------------------------------------+------------------------
Reporter: Natalia Bidart | Owner: nobody
Type: Bug | Status: new
Component: Template system | Version: 4.2
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------------+------------------------
Consider the following template code snippet:

{{{
{% autoescape off %}
{{ some_list|join:some_var }}
{% endautoescape %}
}}}

in this case, the items inside `some_list` will not be escaped (matching
the expected behavior) but `some_var` will forcibly be escaped. From the
docs for `autoescape` or `join` I don't think this is expected behavior.

The following testcase illustrates what I think is a bug in the `join`
filter (run inside the `template_tests/filter_tests` folder):
{{{
#!python
from django.template.defaultfilters import escape
from django.test import SimpleTestCase

from ..utils import setup

class RegressionTests(SimpleTestCase):

@setup({"join01": '{{ some_list|join:some_var }}'})
def test_join01(self):
some_list = ["<p>Hello World!</p>", "beta & me",
"<script>Hi!</script>"]
some_var = "<br/>"
output = self.engine.render_to_string("join01", {"some_list":
some_list, "some_var": some_var})
self.assertEqual(output, escape(some_var.join(some_list)))

@setup({"join02": '{% autoescape off %}{{ some_list|join:some_var }}{%
endautoescape %}'})
def test_join02(self):
some_list = ["<p>Hello World!</p>", "beta & me",
"<script>Hi!</script>"]
some_var = "<br/>"
output = self.engine.render_to_string("join02", {"some_list":
some_list, "some_var": some_var})
self.assertEqual(output, some_var.join(some_list))
}}}

Result of this run in current `main` is:
{{{
.F
======================================================================
FAIL: test_join02
(template_tests.filter_tests.test_regression.RegressionTests.test_join02)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/nessita/fellowship/django/django/test/utils.py", line 443,
in inner
return func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^
File "/home/nessita/fellowship/django/tests/template_tests/utils.py",
line 58, in inner
func(self)
File
"/home/nessita/fellowship/django/tests/template_tests/filter_tests/test_regression.py",
line 21, in test_join02
self.assertEqual(output, some_var.join(some_list))
AssertionError: '<p>Hello World!</p>&lt;br/&gt;beta &
me&lt;br/&gt;<script>Hi!</script>' != '<p>Hello World!</p><br/>beta &
me<br/><script>Hi!</script>'

----------------------------------------------------------------------
Ran 2 tests in 0.007s
}}}

--
Ticket URL: <https://code.djangoproject.com/ticket/34578>
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