Allow users to r- their own pull requests

Users want to be able to `r-` their own pull requests when they know the
change will not successfully pass, and want to unapprove before they
have time to push new code.

Users can already effectively unapprove their own pull requests via
other actions, like changing the target branch, pushing new commits, or
closing and re-opening. So allowing them to `r-` instead of having to
use a work-around should also be allowed.

Fixes #40

Author: bryanburgers

homu/main.py

@@ -408,6 +408,13 @@ def record_retry_log(self, src, body):
             [self.repo_label, self.num, src, body],
         )
 
+    @property
+    def author(self):
+        """
+        Get the GitHub login name of the author of the pull request
+        """
+        return self.get_issue().user.login
+
 
 def sha_cmp(short, full):
     return len(short) >= 4 and short == full[:len(short)]
@@ -576,9 +583,18 @@ def parse_commands(body, username, repo_label, repo_cfg, state, my_username,
                     state.change_labels(LabelEvent.APPROVED)
 
         elif word == 'r-':
-            if not verify_auth(username, repo_label, repo_cfg, state,
-                               AuthState.REVIEWER, realtime, my_username):
-                continue
+            # Allow the author of a pull request to unapprove their own PR. The
+            # author can already perform other actions that effectively
+            # unapprove the PR (change the target branch, push more commits,
+            # etc.) so allowing them to directly unapprove it is also allowed.
+
+            # Because verify_auth has side-effects (especially, it may leave a
+            # comment on the pull request if the user is not authorized), we
+            # need to do the author check BEFORE the verify_auth check.
+            if state.author != username:
+                if not verify_auth(username, repo_label, repo_cfg, state,
+                                   AuthState.REVIEWER, realtime, my_username):
+                    continue
 
             state.approved_by = ''
             state.save()