ImportError: cannot import name 'soft_unicode' from 'markupsafe' (/usr/local/lib/python3.9/site-packages/markupsafe/__init__.py)

Bug

We've an error on the pipeline:

    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/builds/confirm/translucent/setup.py", line 64, in <module>
        setup(
      File "/usr/local/lib/python3.9/site-packages/setuptools/__init__.py", line 155, in setup
        return distutils.core.setup(**attrs)
      File "/usr/local/lib/python3.9/site-packages/setuptools/_distutils/core.py", line 148, in setup
        return run_commands(dist)
      File "/usr/local/lib/python3.9/site-packages/setuptools/_distutils/core.py", line 163, in run_commands
        dist.run_commands()
      File "/usr/local/lib/python3.9/site-packages/setuptools/_distutils/dist.py", line 967, in run_commands
        self.run_command(cmd)
      File "/usr/local/lib/python3.9/site-packages/setuptools/_distutils/dist.py", line 986, in run_command
        cmd_obj.run()
      File "/builds/confirm/translucent/setup.py", line 49, in run
        self.build_django_static_files()
      File "/builds/confirm/translucent/setup.py", line 35, in build_django_static_files
        from confirm.translucent.builder import Builder, BASE_DIR, COMPONENTS_DIR, TEMPLATES_DIR
      File "/builds/confirm/translucent/confirm/translucent/builder.py", line 13, in <module>
        from jinja2 import Environment, FileSystemLoader
      File "/usr/local/lib/python3.9/site-packages/jinja2/__init__.py", line 12, in <module>
        from .environment import Environment
      File "/usr/local/lib/python3.9/site-packages/jinja2/environment.py", line 25, in <module>
        from .defaults import BLOCK_END_STRING
      File "/usr/local/lib/python3.9/site-packages/jinja2/defaults.py", line 3, in <module>
        from .filters import FILTERS as DEFAULT_FILTERS  # noqa: F401
      File "/usr/local/lib/python3.9/site-packages/jinja2/filters.py", line 13, in <module>
        from markupsafe import soft_unicode
    ImportError: cannot import name 'soft_unicode' from 'markupsafe' (/usr/local/lib/python3.9/site-packages/markupsafe/__init__.py)
    ----------------------------------------

Root Cause

The root cause for this issue is described in this Jinja issue & this markupsafe issue.

• Jinja 2defines the requirement markupsafe>=0.23 without upper boundary
• Markupsafe 2.1.0 removes the deprecated soft_unicode in favour of soft_str right in this PR

The issue is fixed in the latest Jinja2 versions (e.g. 3.0.3), as these are using the new soft_str. However, we've this requirement defined:

Jinja2<3.0>2.11.3

We need to do that, because sphinx-js doesn't work with newer Jinja versions.
The project seems to be in slumber mode, since a user already asked this.

We now have the following issue:

• According to the maintainer everybody should update to the latest Jinja version.
• However, we can't do that because of sphinx-js

I suggest we version-pin Markupsafe to <2.1.0