Issue with private inheritance in generated rst

[jsturdy]

Hi, I've been trying out this tool on a couple of projects where I'm trying to simplify and consolidate the documentation procedure and it's been working quite well.

However, I've run into a small issue with a part of the code involving generation of inheritance diagrams where it appears that the jinja templating is expanding into invalid rst, resulting in the following warning:

WARNING: Explicit markup ends without a blank line; unexpected unindent.

Here is the configuration I'm using:

 autoapi_type = "python"
 autoapi_python_use_implicit_namespaces = True
 autoapi_dirs = [
     "{}".format(os.getenv("PYTHONSOURCE")),
 ]
 autoapi_add_toctree_entry = False
 autoapi_keep_files = True
 autoapi_options = [
     "members",
     "undoc-members",
     "private-members",
     "show-inheritance",
     "special-members",
     "show-inheritance-diagram",
     "show-module-summary",
 ]
 autoapi_ignore = ["*migrations*", "*conf.py", "*setup.py"]
 autoapi_template_dir = "_templates/autoapi"

And here is an example of the generated rst:

 .. py:class:: Prompt(completekey='tab', stdin=None, stdout=None)                                                                                                                                                                                                                                                                                                            
                                                                                                                                                                                                                                                                                                                                                                             
    Bases: :class:`cmd.Cmd`                                                                                                                                                                                                                                                                                                                                                  
                                                                                                                                                                                                                                                                                                                                                                             
    .. autoapi-inheritance-diagram:: common.prompt.Prompt                                                                                                                                                                                                                                                                                         
       :parts: 1                                                                                                                                                                                                                                                                                                                                                             
 :private-bases:                                                                                                                                                                                                                                                                                                                                                             
    Class defining command line interface prompt.                                                                                                                                                                                                                                                                                                                            

    .. note ::                                                                                                                                                                                                                                                                                                                                                               
                                                                                                                                                                                                                                                                                                                                                                             
       This is a base class and it can (should) be extended                                                                                                                                                                                                                                                                                                                  

which results in the following docs (using sphinx-rtd-theme)

and here is what I would expect it to look like:

.. py:class:: Prompt(completekey='tab', stdin=None, stdout=None)                                                                                                                                                                                                                                                                                                             
                                                                                                                                                                                                                                                                                                                                                                             
   Bases: :class:`cmd.Cmd`                                                                                                                                                                                                                                                                                                                                                   
                                                                                                                                                                                                                                                                                                                                                                             
   .. autoapi-inheritance-diagram:: common.prompt.Prompt                                                                                                                                                                                                                                                                                          
      :parts: 1                                                                                                                                                                                                                                                                                                                                                              
      :private-bases:                                                                                                                                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                                                                                                                                                             
   Class defining command line interface prompt.                                                                                                                                                                                                                                                                                                                             

   .. note ::                                                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                                                             
      This is a base class and it can (should) be extended                                                                                                                                                                                                                                                                                                                   

If I modify the autoapi/templates/python/classes.rst template I can get the expected behaviour (but I'm not an expert in jinja template syntax, so I don't know if it is the "correct" way to fix the root issue)

14c14,16
<       {% if "private-members" in autoapi_options %}:private-bases:{% endif %}
---
>       {% if "private-members" in autoapi_options %}
>       :private-bases:
>       {% endif %}

which results in:

I am working with an older code base, so using python 2.7, but I did a minimal change to fix print statements and was able to obtain the same result with python 3.8 (both in a conda environment).

For the python 2.7 env, the package versions are (removed other matches, but can add them if you think it's relevant):

Jinja2==2.10.1
Sphinx==1.8.5
sphinx-autoapi==1.3.0
sphinx-rtd-theme==0.4.3

and for the python 3.8 env, the package versions are:

pip freeze|egrep -i (sphinx|autoapi|jinja)
Jinja2==2.10.3
Sphinx==2.4.3
sphinx-autoapi==1.3.0
sphinx-rtd-theme==0.4.3

Please let me know if any additional information would be helpful.

[AWhetter]

Thanks for the detailed report! The fix for this will go out in the next release.