Sync External versions to our database

This is just an initial proof of concept.
We still need to update the External type properly,
and do lots of other work.
This is just a start to show how we can sync and build them.

Author: ericholscher

readthedocs/projects/constants.py

@@ -333,3 +333,8 @@
     'https://gitlab.com/{user}/{repo}/'
     '{action}/{version}{docroot}{path}{source_suffix}'
 )
+
+DEFAULT_GIT_PATTERN = 'refs/heads/*:refs/remotes/origin/*'
+GITHUB_GIT_PATTERN = 'refs/pull/*/head:refs/remotes/origin/external/*'
+GITLAB_GIT_PATTERN = 'refs/merge-requests/*/head:refs/remotes/origin/external/*'
+BITBUCKET_GIT_PATTERN = 'refs/pull/*/head:refs/remotes/origin/external/*'

readthedocs/vcs_support/backends/git.py

@@ -11,6 +11,7 @@
 from git.exc import BadName, InvalidGitRepositoryError
 
 from readthedocs.config import ALL
+from readthedocs.projects.constants import GITHUB_GIT_PATTERN, DEFAULT_GIT_PATTERN
 from readthedocs.projects.exceptions import RepositoryError
 from readthedocs.projects.validators import validate_submodule_url
 from readthedocs.vcs_support.base import BaseVCS, VCSVersion
@@ -55,9 +56,12 @@ def update(self):
         super().update()
         if self.repo_exists():
             self.set_remote_url(self.repo_url)
-            return self.fetch()
+            self.fetch()
+            return
         self.make_clean_working_dir()
-        return self.clone()
+        self.clone()
+        # Do a fetch to make sure we get all external versions
+        self.fetch()
 
     def repo_exists(self):
         try:
@@ -144,7 +148,8 @@ def use_shallow_clone(self):
         return not self.project.has_feature(Feature.DONT_SHALLOW_CLONE)
 
     def fetch(self):
-        cmd = ['git', 'fetch', '--tags', '--prune', '--prune-tags']
+        cmd = ['git', 'fetch', 'origin', DEFAULT_GIT_PATTERN, GITHUB_GIT_PATTERN,
+               '--tags', '--prune', '--prune-tags']
 
         if self.use_shallow_clone():
             cmd.extend(['--depth', str(self.repo_depth)])