actions: support non-indexed decision tasks (#447)

Usually we can look up the on-push decision task using the tc index, however
that doesn't work for pull requests, which are generally not indexed, and if
they were, wouldn't share the same namespace.  In that case, assume the
decision task id is the action task's group id.

Author: jcristau

src/taskgraph/actions/add_new_jobs.py

@@ -40,7 +40,7 @@
 )
 def add_new_jobs_action(parameters, graph_config, input, task_group_id, task_id):
     decision_task_id, full_task_graph, label_to_taskid = fetch_graph_and_labels(
-        parameters, graph_config
+        parameters, graph_config, task_group_id=task_group_id
     )
 
     to_run = []

src/taskgraph/actions/rebuild_cached_tasks.py

@@ -18,7 +18,7 @@ def rebuild_cached_tasks_action(
     parameters, graph_config, input, task_group_id, task_id
 ):
     decision_task_id, full_task_graph, label_to_taskid = fetch_graph_and_labels(
-        parameters, graph_config
+        parameters, graph_config, task_group_id=task_group_id
     )
     cached_tasks = [
         label

src/taskgraph/actions/retrigger.py

@@ -144,7 +144,7 @@ def retrigger_decision_action(parameters, graph_config, input, task_group_id, ta
 )
 def retrigger_action(parameters, graph_config, input, task_group_id, task_id):
     decision_task_id, full_task_graph, label_to_taskid = fetch_graph_and_labels(
-        parameters, graph_config
+        parameters, graph_config, task_group_id=task_group_id
     )
 
     task = taskcluster.get_task_definition(task_id)
@@ -201,7 +201,7 @@ def rerun_action(parameters, graph_config, input, task_group_id, task_id):
     task = taskcluster.get_task_definition(task_id)
     parameters = dict(parameters)
     decision_task_id, full_task_graph, label_to_taskid = fetch_graph_and_labels(
-        parameters, graph_config
+        parameters, graph_config, task_group_id=task_group_id
     )
     label = task["metadata"]["name"]
     if task_id not in label_to_taskid.values():
@@ -259,7 +259,7 @@ def _rerun_task(task_id, label):
 )
 def retrigger_multiple(parameters, graph_config, input, task_group_id, task_id):
     decision_task_id, full_task_graph, label_to_taskid = fetch_graph_and_labels(
-        parameters, graph_config
+        parameters, graph_config, task_group_id=task_group_id
     )
 
     suffixes = []

src/taskgraph/actions/util.py

@@ -32,8 +32,15 @@ def get_parameters(decision_task_id):
     return get_artifact(decision_task_id, "public/parameters.yml")
 
 
-def fetch_graph_and_labels(parameters, graph_config):
-    decision_task_id = find_decision_task(parameters, graph_config)
+def fetch_graph_and_labels(parameters, graph_config, task_group_id=None):
+    try:
+        # Look up the decision_task id in the index
+        decision_task_id = find_decision_task(parameters, graph_config)
+    except KeyError:
+        if not task_group_id:
+            raise
+        # Not found (e.g. from github-pull-request), fall back to the task group id.
+        decision_task_id = task_group_id
 
     # First grab the graph and labels generated during the initial decision task
     full_task_graph = get_artifact(decision_task_id, "public/full-task-graph.json")