Error with HTML exporter when running Checkbox in a virtual environment

Steps
=====

Install Checkbox using the mk-venv script:

git clone git+ssh://<email address hidden>/checkbox-ng
cd checkbox-ng
./mk-venv

Activate the venv and start checkbox:

source path/to/venv/bin/activate
(venv) $ checkbox-cli

Expected result
===============

Checkbox can run and export HTML report using the default Jinja2 exporter.

Actual result
=============

An error is displayed before the Test Plan selection screen:

-------------------------------------
ERROR:plainbox.session.assistant:Problems encountered when loading com.canonical.plainbox:exporters provider: [PlugInError("Problem in unit definition, \x1b[31m\x1b[1merror\x1b[0m: /home/pierre/dev/checkbox-project/checkbox-ng/plainbox/impl/providers/exporters/units/exporter.pxu:4: exporter 'html', field 'entry_point', cannot import name 'environmentfilter' from 'jinja2' (/home/pierre/dev/checkbox-project/checkbox-ng/venv/lib/python3.8/site-packages/Jinja2-3.1.2-py3.8.egg/jinja2/__init__.py)")]
-------------------------------------

When a test run completes, the HTML report cannot be generated:

-------------------------------------
ERROR:checkbox-ng.launcher.stages:Problem with a '1_text_to_screen' report using 'com.canonical.plainbox::text' exporter sent to 'python://stdout' transport.
ERROR:checkbox-ng.launcher.stages:Problem with a '2_html_file' report using 'com.canonical.plainbox::html' exporter sent to '/home/pierre/.local/share/checkbox-ng/submission_2022-07-05T13.14.15.824544.html' transport.
ERROR:checkbox-ng.launcher.stages:Problem with a '2_junit_file' report using 'com.canonical.plainbox::junit' exporter sent to '/home/pierre/.local/share/checkbox-ng/submission_2022-07-05T13.14.15.824544.junit.xml' transport.
ERROR:checkbox-ng.launcher.stages:Problem with a '2_tar_file' report using 'com.canonical.plainbox::tar' exporter sent to '/home/pierre/.local/share/checkbox-ng/submission_2022-07-05T13.14.15.824544.tar.xz' transport.
-------------------------------------

Investigation
=============

When running mk-venv, the latest versions of each required Python packages is installed. At time of writing, it means Jinja2 v3.1.2. However, in v3.1.0[1], Markup and escape were deprecated and moved to another Python package (markupsafe). See jinja2 src[2] for more info.

For now, Ubuntu repos are still using older versions of Jinja2[3].

Workaround
==========

Install Jinja2 and MarkupSafe with versions similar to the ones in the repos of a given Ubuntu version. For instance, to match the versions found in Ubuntu 20.04:

(venv) $ pip install jinja2==2.10.1
(venv) $ pip install markupsafe==1.1.0

[1] https://jinja.palletsprojects.com/en/3.1.x/changes/?highlight=markup#version-3-1-0
[2] https://github.com/pallets/jinja/pull/1544/files#diff-99868302c0e75a5c181912aab0e396266e2ce25fd7b0b8f29684df74eef49984L836
[3] https://packages.ubuntu.com/search?keywords=python3-jinja2&searchon=names&suite=all&section=all