README.md in theme directory overrides index.md in docs

[ruuda]

Summary

MkDocs will generate index.html from README.md in the theme directory, even if index.md exists in the docs directory.

Steps to reproduce

Consider the following minimal example:

├── docs
│   └── index.md
├── mkdocs.yml
└── theme
    ├── main.html
    └── README.md

docs/index.md:

The right index.

theme/README.md:

The wrong index.

theme/main.html:

{{ page.content }}

mkdocs.yml:

site_name: Repro
theme:
  name: null
  custom_dir: theme
nav:
  - Overview: index.md

After running mkdocs build, the following index.html is produced:

<p>The wrong index.</p>

Furthermore, mkdocs build emits the following message:

INFO    -  The following pages exist in the docs directory, but are not included in the "nav" configuration:
  - README.md 

This is especially surprising, because the the docs say:

If both an index.md file and a README.md file are found in the same directory, then the index.md file is used and the README.md file is ignored.

I would expect markdown files in the theme directory to not affect how the documentation is built, unless they are specifically included from a template.

$ mkdocs --version
mkdocs, version 1.0.4 from /usr/lib/python3.7/site-packages/mkdocs (Python 3.7)

[waylan]

I expect this was fixed in #1672, which will be available in the next release. However, it occurs to me that perhaps we should exclude all Markdown files from the theme directory, or at least README files. A Theme should not be able to add "pages" to a site and README files in a theme would not be content either.