Taskcluster: run tidy on PRs

etc/taskcluster/decision_task.py

@@ -10,11 +10,11 @@ from decisionlib import CONFIG, SHARED
 
 
 def main(task_for):
-    assert CONFIG.git_ref.startswith("refs/heads/")
-    branch = CONFIG.git_ref[len("refs/heads/"):]
-    CONFIG.treeherder_repository_name = "servo-" + (
-        branch if not branch.startswith("try-") else "try"
-    )
+    if CONFIG.git_ref.startswith("refs/heads/"):
+        branch = CONFIG.git_ref[len("refs/heads/"):]
+        CONFIG.treeherder_repository_name = "servo-" + (
+            branch if not branch.startswith("try-") else "try"
+        )
 
     if task_for == "github-push":
         # FIXME https://github.com/servo/servo/issues/22325 implement these:
@@ -72,6 +72,16 @@ def main(task_for):
         for function in by_branch_name.get(branch, []):
             function()
 
+    elif task_for == "github-pull-request":
+        CONFIG.treeherder_repository_name = "servo-prs"
+
+        # We want the merge commit that GitHub creates for the PR.
+        # The event does contain a `pull_request.merge_commit_sha` key, but it is wrong:
+        # https://github.com/servo/servo/pull/22597#issuecomment-451518810
+        CONFIG.git_sha_is_current_head()
+
+        tidy_untrusted()
+
     # https://tools.taskcluster.net/hooks/project-servo/daily
     elif task_for == "daily":
         daily_tasks_setup()
@@ -120,6 +130,22 @@ windows_sparse_checkout = [
 ]
 
 
+def tidy_untrusted():
+    return (
+        decisionlib.DockerWorkerTask("Tidy")
+        .with_worker_type("servo-docker-untrusted")
+        .with_treeherder("Linux x64", "Tidy")
+        .with_max_run_time_minutes(60)
+        .with_dockerfile(dockerfile_path("build"))
+        .with_env(**build_env, **unix_build_env, **linux_build_env)
+        .with_repo()
+        .with_script("""
+            ./mach test-tidy --no-progress --all
+        """)
+        .create()
+    )
+
+
 def linux_tidy_unit_docs():
     return (
         linux_build_task("Tidy + dev build + unit tests + docs")
@@ -452,7 +478,7 @@ def daily_tasks_setup():
         "expires": SHARED.from_now_json(log_artifacts_expire_in),
     })
 
-    # Unlike when reacting to a GitHub event,
+    # Unlike when reacting to a GitHub push event,
     # the commit hash is not known until we clone the repository.
     CONFIG.git_sha_is_current_head()
 
@@ -511,7 +537,6 @@ def linux_build_task(name, *, build_env=build_env):
         .with_dockerfile(dockerfile_path("build"))
         .with_env(**build_env, **unix_build_env, **linux_build_env)
         .with_repo()
-        .with_index_and_artifacts_expire_in(build_artifacts_expire_in)
     )