Support docs from the root directory.

[athackst]

Per discussion #3062 this change would allow users to build a mkdocs site from the root directory.

This change removes the validation checks for the site directory to not be within the docs directory.
If the site folder is within the docs directory, it will mark them as 'EXCLUDED'

Tested:

• added unit test

[athackst]

It might be worth considering an "ignore" option for InclusionLevel which would additionally not copy to the server, although I think the '--clean' option provides most of the benefit already.

[oprypin]

Thanks for pushing this forward. Sadly, I think this is too many steps that users would have to take in order to use this. If someone runs into this unprepared, confusion is fully guaranteed.
I think this --clean in particular is nasty for this, and maybe that "draft" feature was a mistake in general.
I want to more comprehensively solve all of these small issues before simply unlocking this

[athackst]

To be clear, it's still usable as is. A normal user would not even notice the extra site folder since nothing links to it. It just copies more than it needs to into the temp directory that serves the site.

It performs as expected on a normal build.

[athackst]

@oprypin I updated this one after rebasing on top of #3476

The site directory is now appropriately marked as excluded both in build and serve.

[squidfunk]

Note that advertising that site_dir can be contained within docs_dir, albeit it might be supported, could break a lot of plugins that do not source their files from the Files collection, but use something like glob or other ways of enumerating files in the docs_dir. One might argue that those approaches are not idiomatic, but I've seen them more than often (and am guilty as well), so this change has quite some potential for frustration.

[athackst]

I wouldn't advocate for changing the default from the 'docs' directory. I think there are legitimate use cases for wanting to call mkdocs from root though. It's a feature that's been requested a fair amount through mkdocs history.

[oprypin]

@athackst We will get this working for sure. I would like to propose a different "explicit" approach though - see #3519

[oprypin]

My last conclusion on this was that the feature request is good but the exact change I wanted to be done differently.

So, I was using this PR as if it's an issue and the actual pull request I wanted to merge is #3519.
However that one got stuck - didn't go into 1.6.0 and its status is unknown.
I'll leave it because I think it's the best direction overall.

To avoid confusion, maybe this pull request should be closed and an issue opened instead.