3.5.4-->4.0.0 sphinx + sphinx-websupport:

[Mathiasdm]

Describe the bug
We get a stacktrace when trying to WebSupport(srcdir=,
builddir=,
docroot='pages',
storage=storage_backend).build()
Our storage_backend is a dummy backend.

  File "./test.py", line 48, in <module>
    support.build()
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinxcontrib/websupport/core.py", line 144, in build
    app.build()
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinx/application.py", line 350, in build
    self.builder.build_update()
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 294, in build_update
    len(to_build))
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 356, in build
    self.write(docnames, list(updated_docnames), method)
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 530, in write
    self._write_serial(sorted(docnames))
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 540, in _write_serial
    self.write_doc(docname, doctree)
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinxcontrib/websupport/builder.py", line 102, in write_doc
    self.handle_page(docname, ctx, event_arg=doctree)
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinxcontrib/websupport/builder.py", line 167, in handle_page
    templatename, event_arg)
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinxcontrib/websupport/builder.py", line 156, in _render_page
    template_module = template.make_module(ctx)
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/jinja2/environment.py", line 1155, in make_module
    return TemplateModule(self, self.new_context(vars, shared, locals))
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/jinja2/environment.py", line 1238, in __init__
    body_stream = list(template.root_render_func(context))
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinx/themes/basic/page.html", line 15, in root
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/alabaster/layout.html", line 58, in root
    </div>
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinx/themes/basic/../basic/layout.html", line 257, in root
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinx/themes/basic/../basic/layout.html", line 410, in block_css
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/jinja2/sandbox.py", line 462, in call
    return __context.call(__obj, *args, **kwargs)
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/jinja2/runtime.py", line 290, in call
    return __obj(*args, **kwargs)
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/jinja2/runtime.py", line 675, in __call__
    return self._invoke(arguments, autoescape)
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/jinja2/runtime.py", line 679, in _invoke
    rv = self._func(*arguments)
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/sphinx/themes/basic/../basic/layout.html", line 211, in macro
    {%- endblock %}
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/jinja2/sandbox.py", line 460, in call
    if not __self.is_safe_callable(__obj):
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/jinja2/sandbox.py", line 360, in is_safe_callable
    getattr(obj, "unsafe_callable", False) or getattr(obj, "alters_data", False)
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/jinja2/runtime.py", line 753, in __getattr__
    return self._fail_with_undefined_error()
  File "/repo/mdemare/tmp/sphinxtest/env/lib/python3.6/site-packages/jinja2/runtime.py", line 747, in _fail_with_undefined_error
    raise self._undefined_exception(self._undefined_message)
jinja2.exceptions.UndefinedError: 'css_tag' is undefined

To Reproduce
Steps to reproduce the behavior:

virtualenv env
source env/bin/activate
pip install sphinx==4.0.0 sphinxcontrib-websupport
chmod +x test.py
./test.py

Additional files to put in the current directory:

1. An empty conf.py
2. index.rst only containing the text 'foo'
3. test.py:

#!/usr/bin/env python3

import sphinxcontrib.websupport
from sphinxcontrib.websupport import WebSupport

class DummyStorageBackend(sphinxcontrib.websupport.storage.StorageBackend):
    """Sphinx requires a storage backend -- for now, don't use an actual one as we don't use the comments"""

    def __init__(self):
        pass

    def pre_build(self):
        pass

    def add_node(self, id, document, source):
        pass

    def has_node(self, id):
        return False

    def post_build(self):
        pass

    def add_comment(self, text, displayed, username, time, proposal, node_id, parent_id, moderator):
        pass

    def delete_comment(self, comment_id, username, moderator):
        pass

    def get_data(self, node_id, username, moderator):
        pass

    def get_metadata(self, docname, moderator):
        pass

    def process_vote(self, comment_id, username, value):
        pass

    def update_username(self, old_username, new_username):
        pass

    def accept_comment(self, comment_id):
        pass


storage_backend = DummyStorageBackend()
support = WebSupport(srcdir=".", builddir="build", docroot="pages", storage=storage_backend)
support.build()

Expected behavior
Successful call of support.build()

Your project
n/a

Screenshots
n/a

Environment info

• OS: Linux
• Python version: 3.6
• Sphinx version: 4.0.0
• Sphinx extensions: sphinx-websupport
• Extra tools: [e.g. Browser, tex or something else]

Additional context
Add any other context about the problem here.

• [e.g. URL or Ticket]