ci: add route to index docker-images by PR number

Author: ahal

src/taskgraph/transforms/docker_image.py

@@ -256,3 +256,29 @@ def fill_template(config, tasks):
             }
 
         yield taskdesc
+
+
+@transforms.add
+def add_pr_route(config, tasks):
+    """Taskgraph builds several docker-images that get used externally.
+
+    Indexing these images by pull request number, allows us to easily test them
+    in external repos using the `indexed-image` image definition type.
+    """
+    if not (pr_number := config.params.get("pull_request_number")):
+        yield from tasks
+        return
+
+    PR_ROUTE = "index.{trust-domain}.v2.{project}.pr.{pr-number}.latest.{product}.{task-name}"
+    subs = {
+        "trust-domain": config.graph_config["trust-domain"],
+        "project": config.params["project"],
+        "pr-number": pr_number,
+        "product": "docker-image",
+    }
+
+    for task in tasks:
+        subs["task-name"] = task["attributes"]["image_name"]
+        routes = task.setdefault("routes", [])
+        routes.append(PR_ROUTE.format(**subs))
+        yield task

taskcluster/test/params/main-repo-pull-request.yml

@@ -17,6 +17,7 @@ moz_build_date: '20220421203159'
 optimize_target_tasks: true
 owner: [email protected]
 project: taskgraph
+pull_request_number: 123
 pushdate: 0
 pushlog_id: '0'
 repository_type: git