Bug 1667482 - [taskgraph] Don't fail if last backstop decision task is still running, r=marco

Differential Revision: https://phabricator.services.mozilla.com/D92096

taskcluster/taskgraph/test/test_util_backstop.py

@@ -66,6 +66,16 @@ def params():
             True,
             id="no previous backstop",
         ),
+        pytest.param(
+            {
+                "index": DEFAULT_RESPONSES["index"],
+                "status": DEFAULT_RESPONSES["status"],
+                "artifact": {"status": 404},
+            },
+            {"pushlog_id": 1},
+            False,
+            id="previous backstop not finished",
+        ),
         pytest.param(
             DEFAULT_RESPONSES,
             {

taskcluster/taskgraph/util/backstop.py

@@ -4,6 +4,8 @@
 
 from __future__ import absolute_import, print_function, unicode_literals
 
+from requests import HTTPError
+
 from taskgraph.util.taskcluster import (
     find_task_id,
     get_artifact,
@@ -61,7 +63,17 @@ def is_backstop(
         # If the last backstop failed its decision task, make this a backstop.
         return True
 
-    last_pushdate = get_artifact(last_backstop_id, 'public/parameters.yml')["pushdate"]
+    try:
+        last_pushdate = get_artifact(last_backstop_id, 'public/parameters.yml')["pushdate"]
+    except HTTPError as e:
+        # If the last backstop decision task exists in the index, but
+        # parameters.yml isn't available yet, it means the decision task is
+        # still running. If that's the case, we can be pretty sure the time
+        # component will not cause a backstop, so just return False.
+        if e.response.status_code == 404:
+            return False
+        raise
+
     if (pushdate - last_pushdate) / 60 >= time_interval:
         return True
     return False