Jinja UndefinedError with header tags

[NiklasRosenstein]

I get this error when I place a < or > in a Markdown header, like

# <some.hpp>

Or even when I juse HTML tags like

<h2 id="nr.pvrq2.RenderJob">RenderJob</h2>

---

Error traceback:

  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\mkdocs\__main__.py", line 127, in serve_command
    livereload=livereload
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\mkdocs\commands\serve.py", line 82, in serve
    config = builder()
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\mkdocs\commands\serve.py", line 78, in builder
    build(config, live_server=live_server, dirty=dirty)
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\mkdocs\commands\build.py", line 379, in build
    build_pages(config, dirty=dirty)
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\mkdocs\commands\build.py", line 332, in build_pages
    dump_json)
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\mkdocs\commands\build.py", line 212, in _build_page
    output_content = template.render(context)
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\jinja2\environment.py", line 989, in render
    return self.environment.handle_exception(exc_info, True)
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\jinja2\environment.py", line 754, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\jinja2\_compat.py", line 37, in reraise
    raise value.with_traceback(tb)
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\material\main.html", line 1, in top-level template code
    {% extends "base.html" %}
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\material\base.html", line 87, in top-level template code
    {% block site_nav %}
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\material\base.html", line 92, in block "site_nav"
    {% include "partials/nav.html" %}
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\material\partials\nav.html", line 18, in top-level template code
    {% include "partials/nav-item.html" %}
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\material\partials\nav-item.html", line 19, in top-level template code
    {% include "partials/nav-item.html"  %}
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\material\partials\nav-item.html", line 29, in top-level template code
    {% set toc_ = (toc_ | first).children %}
  File "c:\users\niklas\repos\pydoc-markdown\.env\lib\site-packages\jinja2\environment.py", line 408, in getattr
    return getattr(obj, attribute)
jinja2.exceptions.UndefinedError: No first item, sequence was empty.

[squidfunk]

Please provide the complete source of the page which is causing the issue (you can replace with lorem ipsum, though) and some information on versions. See the issue template for this reason.

[NiklasRosenstein]

Version

mkdocs-material==1.0.2

index.md

<h1 id="nr.pvrq2">nr.pvrq2</h1>

FooBar Baz

mkdocs.yml

site_name: My Docs
theme: material

Error

[...]
  File "c:\python35-32\lib\site-packages\mkdocs\commands\build.py", line 212, in _build_page
    output_content = template.render(context)
  File "c:\python35-32\lib\site-packages\jinja2\environment.py", line 989, in render
    return self.environment.handle_exception(exc_info, True)
  File "c:\python35-32\lib\site-packages\jinja2\environment.py", line 754, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "c:\python35-32\lib\site-packages\jinja2\_compat.py", line 37, in reraise
    raise value.with_traceback(tb)
  File "c:\python35-32\lib\site-packages\material\main.html", line 1, in top-level template code
    {% extends "base.html" %}
  File "c:\python35-32\lib\site-packages\material\base.html", line 87, in top-level template code
    {% block site_nav %}
  File "c:\python35-32\lib\site-packages\material\base.html", line 92, in block "site_nav"
    {% include "partials/nav.html" %}
  File "c:\python35-32\lib\site-packages\material\partials\nav.html", line 18, in top-level template code
    {% include "partials/nav-item.html" %}
  File "c:\python35-32\lib\site-packages\material\partials\nav-item.html", line 29, in top-level template code
    {% set toc_ = (toc_ | first).children %}
  File "c:\python35-32\lib\site-packages\jinja2\environment.py", line 408, in getattr
    return getattr(obj, attribute)
jinja2.exceptions.UndefinedError: No first item, sequence was empty.

[NiklasRosenstein]

I also just tried it with 1.0.3

[NiklasRosenstein]

Actually I can not reproduce the # <some.hpp> example anymore, so ignore that for now. But the HTML header tags issue is reproducible.

[squidfunk]

Well, it has to do with the table of contents extension. The TOC cannot be generated when you use HTML tags, only when using the Markdown. The error shouldn't be there and there should be no TOC. Will fix it as soon as I find the time.

EDIT: for now you can just use the standard Markdown Syntax and everything should be fine.

# nr.pvrq2

[NiklasRosenstein]

The TOC cannot be generated when you use HTML tags, only when using the Markdown. The error shouldn't be there and there should be no TOC. Will fix it as soon as I find the time.

By the way, do you know why that is? Is it a limitation or design decision of MkDocs? I need to generate HTML tags to assign them correct IDs, and eventually additional styling (eg. parts of the header in a smaller font and/or in monospace).

[squidfunk]

This is not a limitation of MkDocs, but of the Python Markdown Extensions MkDocs uses. Monospaced and smaller text is possible and supported by Material:

# Header with `code` and <small>small text</small>

You could add your anchor as HTML in the header, though:

# <a id="nr.pvrq2"></a> nr.pvrq2

Untested, may break other stuff.

[squidfunk]

I now know why it breaks - I had to apply a hack to check whether the content contains a h1 headline to see if the page title should be set as a fallback (if it doesn't) and this matches your code exactly. You can fix it temporarily by adding another tag in front of the h1:

<h1 class="" id="nr.pvrq2">nr.pvrq2</h1>

I will provide a fix.

[squidfunk]

Fix #144 is in master now. Please checkout the master and confirm. Instructions on how to use Material from master are here (2 easy steps):

1. http://squidfunk.github.io/mkdocs-material/getting-started/#cloning-from-github
2. http://squidfunk.github.io/mkdocs-material/getting-started/#usage

[squidfunk]

Released in 1.0.4

[NiklasRosenstein]

Thanks, I can confirm it's working now! :)