Addons: get final project (e.g. subproject) (#10745)

Use `unresolved_url` to get the final project requested from the URL. This is
needed for subproject since it's the only place where it's present.

Previously, we were getting the project from the `unresolved_domain` which does
not give us the `subproject` because it's not present in the domain itself.

Tests will be added in
#10685

Closes readthedocs/readthedocs-corporate#1622

readthedocs/proxito/views/hosting.py

@@ -67,10 +67,15 @@ def _resolve_resources(self):
             return None, None, None, None
 
         unresolved_domain = self.request.unresolved_domain
+
+        # Main project from the domain.
         project = unresolved_domain.project
 
         try:
             unresolved_url = unresolver.unresolve_url(url)
+            # Project from the URL: if it's a subproject it will differ from
+            # the main project got from the domain.
+            project = unresolved_url.project
             version = unresolved_url.version
             filename = unresolved_url.filename
             build = version.builds.last()
@@ -248,6 +253,8 @@ def _v0(self, project, version, build, filename, user):
                 " AND IT'S GOING TO CHANGE COMPLETELY -- DO NOT USE IT!"
             ),
             "projects": {
+                # TODO: return the "parent" project here when the "current"
+                # project is a subproject/translation.
                 "current": ProjectSerializerNoLinks(project).data,
             },
             "versions": {