Custom urlconf breaks automatic redirects

[agjohnson]

When using a custom urlconf, redirects like / -> /en/latest don't seem to work. Instead, a 404 error is returned. There is a similar issue where perhaps a top level request could redirect to en/latest with the prepended prefix -- ie: / to /subpath/foo/en/latest/, though this is less important likely.

To reproduce:

• Give a project a custom urlconf: subpath/$language/$version/$filename
• Browse to the project URL: foo.readthedocs.io/subpath/en/latest/ -- this works
• Browse to the custom root: foo.readthedocs.io/subpath/ -- 404 here, where normall we'd redirect to foo.readthedocs.io/subpath/en/latest/
• Browse to the top level path: foo.readthedocs.io/ -- also 404 here, though this might be harder to resolve

[ericholscher]

I think this is because we're defaulting some of the variables when there's a urlconf. We probably just need to tighten up that logic:

readthedocs.org/readthedocs/proxito/views/utils.py

Lines 79 to 87 in f138d17

	if any([
	not version_slug and final_project.single_version,
	not version_slug and project.urlconf
	]):
	version_slug = final_project.get_default_version()
	if not lang_slug and project.urlconf:
	lang_slug = final_project.language

Something like: if project.urlconf and '$version' not in project.urlconf

[stsewd]

The new proxito implementation doesn't have this problem #10156.

[ericholscher]

@stsewd awesome :)