mkdocs build crashes when navigation.sections is enabled.

• [ X ] I’ve read the contribution guidelines and agree with them

I’ve found a bug and checked that …

• [ X ] … the problem doesn’t occur with the default MkDocs template
• [ X ] … the problem is not in any of my customizations (CSS, JS, template)
• [ X ] … the documentation does not mention anything about my problem
• [ X ] … there are no open or closed issues that are related to my problem

Description

mkdocs build crashes when navigation.sections is enabled.

Expected behavior

was hoping to see the behavior described in the documentation.

Actual behavior

barfs as described below.

Steps to reproduce the bug

mkdoc-material bug

root@annie:/home/don# lxc launch ubuntu/focal/cloud mkdocs -p susdev21 -p default
Creating mkdocs
Starting mkdocs
root@annie:/home/don# lxc exec mkdocs bash
root@mkdocs:~# apt-get update
...
root@mkdocs:~# apt-get install nano git wget python3-pip
...
root@mkdocs:/var/www# pip3 install mkdocs-material
...
root@mkdocs:~# mkdir /var/www/
root@mkdocs:~# cd /var/www
root@mkdocs:/var/www# git clone https://github.com/feurig/digithink.git
Cloning into 'digithink'...
...
root@mkdocs:/var/www# cd digithink/
root@mkdocs:/var/www/digithink# nano mkdocs.yml 
site_name: works4me
theme:
  name: material
  features:
    - navigation.expand
   
root@mkdocs:/var/www/digithink# mkdocs build
INFO    -  Cleaning site directory 
INFO    -  Building documentation to directory: /var/www/digithink/site 
INFO    -  Documentation built in 1.90 seconds 
root@mkdocs:/var/www/digithink# nano mkdocs.yml 
site_name: buggy
theme:
  name: material
  features:
    - navigation.sections

root@mkdocs:/var/www/digithink# mkdocs build
INFO    -  Cleaning site directory 
INFO    -  Building documentation to directory: /var/www/digithink/site 
Traceback (most recent call last):
  File "/usr/local/bin/mkdocs", line 8, in <module>
    sys.exit(cli())
  File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.8/dist-packages/mkdocs/__main__.py", line 152, in build_command
    build.build(config.load_config(**kwargs), dirty=not clean)
  File "/usr/local/lib/python3.8/dist-packages/mkdocs/commands/build.py", line 285, in build
    _build_theme_template(template, env, files, config, nav)
  File "/usr/local/lib/python3.8/dist-packages/mkdocs/commands/build.py", line 108, in _build_theme_template
    output = _build_template(template_name, template, files, config, nav)
  File "/usr/local/lib/python3.8/dist-packages/mkdocs/commands/build.py", line 87, in _build_template
    output = template.render(context)
  File "/usr/lib/python3/dist-packages/jinja2/asyncsupport.py", line 76, in render
    return original_render(self, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/jinja2/environment.py", line 1008, in render
    return self.environment.handle_exception(exc_info, True)
  File "/usr/lib/python3/dist-packages/jinja2/environment.py", line 780, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/lib/python3/dist-packages/jinja2/_compat.py", line 37, in reraise
    raise value.with_traceback(tb)
  File "/usr/local/lib/python3.8/dist-packages/material/404.html", line 4, in <module>
    {% extends "main.html" %}
  File "/usr/local/lib/python3.8/dist-packages/material/main.html", line 4, in <module>
    {% extends "base.html" %}
  File "/usr/local/lib/python3.8/dist-packages/material/base.html", line 129, in <module>
    {% block site_nav %}
  File "/usr/local/lib/python3.8/dist-packages/material/base.html", line 137, in <module>
    {% include "partials/nav.html" %}
  File "/usr/local/lib/python3.8/dist-packages/material/partials/nav.html", line 31, in <module>
    {% include "partials/nav-item.html" %}
  File "/usr/local/lib/python3.8/dist-packages/material/partials/nav-item.html", line 71, in <module>
    {{ render_nav_item(nav_item, path, level) }}
  File "/usr/lib/python3/dist-packages/jinja2/runtime.py", line 583, in _invoke
    rv = self._func(*arguments)
  File "/usr/local/lib/python3.8/dist-packages/material/partials/nav-item.html", line 10, in <module>
    {% if "navigation.sections" in features and level == 1 + (
TypeError: unsupported operand type(s) for +: 'int' and 'str'

Package versions

Python: python --version

root@mkdocs:/var/www/digithink# python3 --version Python 3.8.5

MkDocs: mkdocs --version

root@mkdocs:/var/www/digithink# mkdocs --version mkdocs, version 1.1.2 from /usr/local/lib/python3.8/dist-packages/mkdocs (Python 3.8)

Material: pip show mkdocs-material | grep -E ^Version

root@mkdocs:/var/www/digithink# pip3 show mkdocs-material | grep -E ^Version Version: 6.2.8

Project configuration

#The contents of your mkdocs.yml
# as described above....
site_name: buggy
  theme:
    name: material
    features:
      - navigation.sections

System information

• OS: Ubuntu 20.04

• Browser: Not Relevent

[PsychoBitchy]

Thank you @whiskeysierra You saved my day 😉 I can confirm adding Jinja2>=2.11.1 in requirements.txt + pip install -r requirements.txt saves a lot of headaches.

[feurig]

Thats cool. I will come back to this when I have more time. I opened the issue because you asked me to. I am happy without using the extension.sections and am fine with closing this out.

D.

FWIW when I run mkdocs against itself I get a different error.

root@mkdocs:/var/www/digithink# git clone https://github.com/squidfunk/mkdocs-material.git docs
Cloning into 'docs'...
....
root@mkdocs:/var/www/digithink# mkdocs build
INFO    -  Cleaning site directory 
INFO    -  Building documentation to directory: /var/www/digithink/site 
ERROR   -  Error reading page 'upgrading.md': 'NoneType' object has no attribute 'end'