Note that mkdocs 0.17.5 is needed

mkdocs-1.0.4 fails like this:

0 jakob@brikett:~/gocryptfs-website$ make
LC_ALL=C.UTF-8 LANG=C.UTF-8 mkdocs build --clean
WARNING -  Config value: 'pages'. Warning: The 'pages' configuration option has been deprecated and will be removed in a future release of MkDocs. Use 'nav' instead.
INFO    -  Cleaning site directory
INFO    -  Building documentation to directory: /home/jakob/gocryptfs-website/site
ERROR   -  Error building page 'index.md': Object of type 'Undefined' is not JSON serializable
Traceback (most recent call last):
  File "/home/jakob/bin/mkdocs", line 11, in <module>
    sys.exit(cli())
  File "/usr/local/lib64/python3.6/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib64/python3.6/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib64/python3.6/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib64/python3.6/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib64/python3.6/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/mkdocs/__main__.py", line 163, in build_command
    ), dirty=not clean)
  File "/usr/local/lib/python3.6/site-packages/mkdocs/commands/build.py", line 295, in build
    _build_page(file.page, config, files, nav, env, dirty)
  File "/usr/local/lib/python3.6/site-packages/mkdocs/commands/build.py", line 216, in _build_page
    output = template.render(context)
  File "/usr/local/lib/python3.6/site-packages/jinja2/asyncsupport.py", line 76, in render
    return original_render(self, *args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/jinja2/environment.py", line 1008, in render
    return self.environment.handle_exception(exc_info, True)
  File "/usr/local/lib/python3.6/site-packages/jinja2/environment.py", line 780, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python3.6/site-packages/jinja2/_compat.py", line 37, in reraise
    raise value.with_traceback(tb)
  File "/home/jakob/gocryptfs-website/gocryptfs-readthedocs/main.html", line 1, in top-level template code
    {% extends "base.html" %}
  File "/home/jakob/gocryptfs-website/gocryptfs-readthedocs/base.html", line 30, in top-level template code
    {%- block libs %}
  File "/home/jakob/gocryptfs-website/gocryptfs-readthedocs/main.html", line 19, in block "libs"
    var mkdocs_page_input_path = {{ page.input_path|tojson|safe }};
  File "/usr/local/lib/python3.6/site-packages/mkdocs/utils/filters.py", line 8, in tojson
    return jinja2.Markup(json.dumps(obj, **kwargs))
  File "/usr/lib64/python3.6/json/__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
  File "/usr/lib64/python3.6/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/lib64/python3.6/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/usr/lib64/python3.6/json/encoder.py", line 180, in default
    o.__class__.__name__)
TypeError: Object of type 'Undefined' is not JSON serializable
make: *** [Makefile:2: all] Error 1

2 files changed, 7 insertions, 2 deletions

diff --git a/.travis.yml b/.travis.yml
index 046ab74..24d6b27 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,7 +2,7 @@ language: python
 python:
   - "3.6"
 install:
-  - pip install mkdocs
+  - pip install mkdocs==0.17.5
 script:
   - mkdocs -V
   - make
diff --git a/README.md b/README.md
index 80fd678..0e95091 100644
--- a/README.md
+++ b/README.md
@@ -3,4 +3,9 @@
 This repostitory contains the gocryptfs website that is available at
 https://nuetzlich.net/gocryptfs .
 
-It is generated using mkdocs. On Debian Stretch: `pip3 install mkdocs`
+It is generated using mkdocs. Install using
+
+    pip3 install mkdocs==0.17.5
+
+Note: mkdocs 1.0 [crashes](https://travis-ci.org/rfjakob/gocryptfs-website/builds/456463957)
+with `Object of type 'Undefined' is not JSON serializable`.