[FIX] *: unnecessary warning on r- of forward port

Reminding users that `r-` on a forward port only unreviews *that*
forwardport is useful, as `r+;r-` is not a no-op (all preceding
siblings are still reviewed).

However it is useless if all siblings are not approved or already
merged. So avoid sending the warning in that case.

Fixes #934

forwardport/tests/test_simple.py

@@ -629,6 +629,14 @@ def test_disapproval(env, config, make_repo, users):
                         "sibling forward ports may have to be unapproved "
                         "individually."),
     ]
+    with prod:
+        pr2.post_comment('hansen r-', token=config['role_other']['token'])
+    env.run_crons(None)
+    assert pr2_id.state == 'validated'
+    assert pr2.comments[2:] == [
+        (users['other'], "hansen r+"),
+        (users['other'], "hansen r-"),
+    ], "shouldn't have a warning on r- because it's the only approved PR of the chain"
 
 def test_delegate_fw(env, config, make_repo, users):
     """If a user is delegated *on a forward port* they should be able to approve

runbot_merge/models/pull_requests.py

@@ -796,10 +796,12 @@ def format_help(warn_ignore: bool, address: bool = True) -> str:
                                 pull_request=self.number,
                                 format_args={'user': login, 'pr': self},
                             )
-                        if self.source_id:
+                        if self.source_id.forwardport_ids.filtered(
+                            lambda p: p.reviewed_by and p.state not in ('merged', 'closed')
+                        ):
                             feedback("Note that only this forward-port has been"
-                                     " unapproved, sibling forward ports may "
-                                     "have to be unapproved individually.")
+                                     " unapproved, sibling forward ports may"
+                                     " have to be unapproved individually.")
                         self.unstage("unreviewed (r-) by %s", login)
                     else:
                         msg = "r- makes no sense in the current PR state."