Fix PR review reminder DAG for case where base branch is 2+ levels de…

…ep (#3182)

catalog/dags/maintenance/pr_review_reminders/pr_review_reminders.py

@@ -181,6 +181,12 @@ def get_min_required_approvals(gh: GitHubAPI, pr: dict) -> int:
         else:
             raise e
 
+    if "required_pull_request_reviews" not in branch_protection_rules:
+        # This can happen in the rare case where a PR is multiple branches deep,
+        # e.g. it depends on a branch which depends on a branch which depends on main.
+        # In that case, default to the rules for `main` as a safe default.
+        branch_protection_rules = get_branch_protection(gh, repo, "main")
+
     return branch_protection_rules["required_pull_request_reviews"][
         "required_approving_review_count"
     ]

catalog/tests/dags/maintenance/test_pr_review_reminders.py

@@ -548,3 +548,37 @@ def test_ignores_created_at_and_pings_if_urgent_ready_for_review_event_exists(
     post_reminders("not_set", dry_run=False)
 
     assert pull["number"] in github["posted_comments"]
+
+
+def test_falls_back_to_main_on_multiple_branch_levels(
+    github,
+):
+    # No need to parametrize this, only need to test the one case
+    # Make branch protection rules for a branch one-off main
+    github["branch_protection"]["openverse"]["non_main"] = {}
+    past_due_pull = make_pull(Urgency.LOW, old=True, base_branch="not_main")
+    past_due_pull["requested_reviewers"] = [
+        make_requested_reviewer(f"reviewer-due-{i}") for i in range(2)
+    ]
+
+    min_required_approvals = 4
+
+    # Always use `main` to exercise fallback for non-main branches
+    _setup_branch_protection_for_branch(
+        github,
+        repo="openverse",
+        branch="main",
+        min_required_approvals=min_required_approvals,
+    )
+
+    github["pulls"] += [past_due_pull]
+    github["pull_reviews"][past_due_pull["number"]] = [
+        make_review("APPROVED"),
+    ] * min_required_approvals
+    github["events"][past_due_pull["number"]] = make_urgent_events(
+        Urgency.LOW, ["review_requested"]
+    )
+
+    post_reminders("not_set", dry_run=False)
+
+    assert past_due_pull["number"] not in github["posted_comments"]