sphinx-themes breaks with Flamingo 1.7.1 and Python 3.10

[SmithChart]

With Python 3.10 the sphinx-themes feature breaks:

make html
. env/bin/activate && \
flamingo build -s settings.py menu.py 
ERROR:flamingo.core.PluginManager:setup of 'flamingo.plugins.SphinxThemes' failed
Traceback (most recent call last):
  File "/home/bbu/scm/ptx/ptx-admin-workplace-mr/ptx-infrastructure-manual/env/lib/python3.10/site-packages/flamingo/core/utils/imports.py", line 19, in acquire
    item = importlib.import_module(item)
  File "/usr/lib/python3.10/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1004, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'flamingo.plugins.SphinxThemes'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/bbu/scm/ptx/ptx-admin-workplace-mr/ptx-infrastructure-manual/env/lib/python3.10/site-packages/flamingo/core/plugins/plugin_manager.py", line 91, in __init__
    plugin_class, plugin_path = acquire(plugin)
  File "/home/bbu/scm/ptx/ptx-admin-workplace-mr/ptx-infrastructure-manual/env/lib/python3.10/site-packages/flamingo/core/utils/imports.py", line 34, in acquire
    item = getattr(module, attr_name)
AttributeError: module 'flamingo.plugins' has no attribute 'SphinxThemes'

Removing the catchall in https://github.com/pengutronix/flamingo/blob/master/flamingo/plugins/__init__.py#L50 yields the actual problem:

$make html
. env/bin/activate && \
flamingo build -s settings.py menu.py 
ERROR:flamingo.core.PluginManager:setup of 'flamingo.plugins.HTML' failed
Traceback (most recent call last):
  File "/home/chris/work/Projects/github/flamingo/flamingo/core/utils/imports.py", line 19, in acquire
    item = importlib.import_module(item)
  File "/home/chris/.pyenv/versions/3.10.2/lib/python3.10/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 992, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 883, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/home/chris/work/Projects/github/flamingo/flamingo/plugins/__init__.py", line 49, in <module>
    from .sphinx_themes.plugin import SphinxThemes  # NOQA
  File "/home/chris/work/Projects/github/flamingo/flamingo/plugins/sphinx_themes/plugin.py", line 10, in <module>
    from sphinx.jinja2glue import _tobool, _todim, _toint, accesskey
  File "/home/chris/work/Projects/ptxadmin/ptx-infrastructure-manual/env/lib/python3.10/site-packages/sphinx/jinja2glue.py", line 20, in <module>
    from sphinx.application import TemplateBridge
  File "/home/chris/work/Projects/ptxadmin/ptx-infrastructure-manual/env/lib/python3.10/site-packages/sphinx/application.py", line 32, in <module>
    from sphinx.config import Config
  File "/home/chris/work/Projects/ptxadmin/ptx-infrastructure-manual/env/lib/python3.10/site-packages/sphinx/config.py", line 21, in <module>
    from sphinx.util import logging
  File "/home/chris/work/Projects/ptxadmin/ptx-infrastructure-manual/env/lib/python3.10/site-packages/sphinx/util/__init__.py", line 41, in <module>
    from sphinx.util.typing import PathMatcher
  File "/home/chris/work/Projects/ptxadmin/ptx-infrastructure-manual/env/lib/python3.10/site-packages/sphinx/util/typing.py", line 37, in <module>
    from types import Union as types_Union
ImportError: cannot import name 'Union' from 'types' (/home/chris/.pyenv/versions/3.10.2/lib/python3.10/types.py)

This was fixed with Sphinx 4.2.0 (https://www.sphinx-doc.org/en/master/changes.html#release-4-2-0-released-sep-12-2021 ) (and PR sphinx-doc/sphinx#9512 ).
But this release (and newer) in incompatible with the flamingo-integration.

[rschwebel]

These are indeed 2 problems: the sphinx update and flamingo failing with python 3.10. Let's focus on the first one in this issue, I'll open another issue afterwards.

[rschwebel]

The Sphinx- and sphinx_rtd_theme update is now in #29.

[rschwebel]

Turns out that problem no 2 above was some left over debug code in a local python 3.10 installation. The testsuite works fine with python 3.10 with #29.

[rschwebel]

@SmithChart Now as #29 has been merged, could you test if this solves this issue?

[SmithChart]

Didn't try this for some time. As of now with Python 3.10.4 and #36 I can build the flamingo documentation as expected.
I am currently testing with:

Sphinx==5.3.0
sphinx-rtd-theme==1.1.1
Pygments==2.13.0

I suggest to close this issue once #36 is merged.

[SmithChart]

#36 is merged -> closing