Add CloudFlare Cache tags support

This lets us purge the CDN more easily.
This requires a version in the files_changed signal.

Author: ericholscher

readthedocs/projects/signals.py

@@ -12,7 +12,7 @@
 project_import = django.dispatch.Signal(providing_args=['project'])
 
 # Used to purge files from the CDN
-files_changed = django.dispatch.Signal(providing_args=['project', 'files'])
+files_changed = django.dispatch.Signal(providing_args=['project', 'version', 'files'])
 
 # Used to force verify a domain (eg. for SSL cert issuance)
 domain_verify = django.dispatch.Signal(providing_args=['domain'])

readthedocs/projects/tasks.py

@@ -1830,6 +1830,7 @@ def _sync_imported_files(version, build, changed_files):
     files_changed.send(
         sender=Project,
         project=version.project,
+        version=version,
         files=changed_files,
     )
 

readthedocs/proxito/views/mixins.py

@@ -126,6 +126,7 @@ def _serve_docs_nginx(self, request, final_project, version_slug, path, download
         response['X-RTD-Version'] = version_slug
         # Needed to strip any GET args, etc.
         response['X-RTD-Path'] = urlparse(path).path
+        response['Cache-Tags'] = f'{final_project.slug}-{version_slug}'
         if hasattr(request, 'rtdheader'):
             response['X-RTD-Version-Method'] = 'rtdheader'
         if hasattr(request, 'subdomain'):