Fix upstreaming of WPT changes

The GitHub Action needs access to Servo repository secrets, so switch to
using the 'pull_request_target' event. Since these PRs have more
complete access to the Servo repository, do not execute the version of
the upstream script that comes with the PR. Instead, simply fetch the
changes. To make this work, the script no longer expects the PR commit
to be checked out, merely that they exist in the repository somewhere.

4 files changed, 30 insertions, 10 deletions

diff --git a/.github/workflows/upstream-wpt-changes.yml b/.github/workflows/upstream-wpt-changes.yml
index d53e5715b9d..0e78e4df583 100644
--- a/.github/workflows/upstream-wpt-changes.yml
+++ b/.github/workflows/upstream-wpt-changes.yml
@@ -1,6 +1,6 @@
 name: WPT export
 on:
-  pull_request:
+  pull_request_target:
     types: ['opened', 'synchronize', 'reopened', 'edited', 'closed']
 
 jobs:
@@ -16,7 +16,8 @@ jobs:
           git init -b main
           git remote add origin ${{ github.event.repository.clone_url}}
           git fetch origin pull/${{ github.event.pull_request.number}}/head:pr --depth ${{ env.PR_FETCH_DEPTH }}
-          git checkout pr
+          git fetch origin master:master --depth 1
+          git checkout master
       - name: Check out wpt
         uses: actions/checkout@v3
         with:
diff --git a/etc/ci/upstream-wpt-changes/test.py b/etc/ci/upstream-wpt-changes/test.py
index 67d83603805..b40af2a48ee 100644
--- a/etc/ci/upstream-wpt-changes/test.py
+++ b/etc/ci/upstream-wpt-changes/test.py
@@ -268,9 +268,12 @@ class TestFullSyncRun(unittest.TestCase):
 
     @classmethod
     def tearDownClass(cls):
+        assert cls.server is not None
         cls.server.shutdown()
 
     def tearDown(self):
+        assert SYNC is not None
+
         # Clean up any old files.
         first_commit_hash = SYNC.local_servo_repo.run("rev-list", "HEAD").splitlines()[
             -1
@@ -286,9 +289,9 @@ class TestFullSyncRun(unittest.TestCase):
                 return [diff, "tmp author", "tmp@tmp.com", "tmp commit message"]
             return diff
 
-        commits = [make_commit_data(diff) for diff in diffs]
-
         # Apply each commit to the repository.
+        orig_sha = SYNC.local_servo_repo.run("rev-parse", "HEAD").strip()
+        commits = [make_commit_data(diff) for diff in diffs]
         for commit in commits:
             patch_file, author, email, message = commit
             SYNC.local_servo_repo.run("apply", os.path.join(TESTS_DIR, patch_file))
@@ -306,6 +309,12 @@ class TestFullSyncRun(unittest.TestCase):
                 },
             )
 
+        # Reset the repository to the original hash, but the commits are still
+        # available until the next `git gc`.
+        last_commit_sha = SYNC.local_servo_repo.run("rev-parse", "HEAD").strip()
+        SYNC.local_servo_repo.run("reset", "--hard", orig_sha)
+        return last_commit_sha
+
     def run_test(
         self, payload_file: str, diffs: list, existing_prs: list[MockPullRequest] = []
     ):
@@ -313,7 +322,8 @@ class TestFullSyncRun(unittest.TestCase):
             payload = json.loads(file.read())
 
         logging.info("Mocking application of PR to servo.")
-        self.mock_servo_repository_state(diffs)
+        last_commit_sha = self.mock_servo_repository_state(diffs)
+        payload["pull_request"]["head"]["sha"] = last_commit_sha
 
         logging.info("Resetting server state")
         assert self.server is not None
@@ -618,4 +628,7 @@ def tearDownModule():
 
 
 if __name__ == "__main__":
+    # Uncomment this line to enable verbose logging.
+    # logging.getLogger().setLevel(logging.INFO)
+
     unittest.main()
diff --git a/etc/ci/upstream-wpt-changes/wptupstreamer/__init__.py b/etc/ci/upstream-wpt-changes/wptupstreamer/__init__.py
index 97b0de8af72..f1b1ef92598 100644
--- a/etc/ci/upstream-wpt-changes/wptupstreamer/__init__.py
+++ b/etc/ci/upstream-wpt-changes/wptupstreamer/__init__.py
@@ -169,7 +169,8 @@ class WPTSync:
                 logging.info(
                     "  → Detected existing upstream PR %s", upstream_pr)
 
-            run = SyncRun(self, servo_pr, AsyncValue(upstream_pr), step_callback)
+            run = SyncRun(self, servo_pr, AsyncValue(
+                upstream_pr), step_callback)
 
             pull_data = payload["pull_request"]
             if payload["action"] in ["opened", "synchronize", "reopened"]:
@@ -189,10 +190,12 @@ class WPTSync:
             return False
 
     def handle_new_pull_request_contents(self, run: SyncRun, pull_data: dict):
+        num_commits = pull_data["commits"]
+        head_sha = pull_data["head"]["sha"]
         is_upstreamable = (
             len(
                 self.local_servo_repo.run(
-                    "diff", f"HEAD~{pull_data['commits']}", "--", UPSTREAMABLE_PATH
+                    "diff", head_sha, f"{head_sha}~{num_commits}", "--", UPSTREAMABLE_PATH
                 )
             )
             > 0
@@ -245,7 +248,8 @@ class WPTSync:
         logging.info("Changing upstream PR title")
         if run.upstream_pr.has_value():
             run.add_step(ChangePRStep(
-                run.upstream_pr.value(), "open", pull_data["title"], pull_data["body"]
+                run.upstream_pr.value(
+                ), "open", pull_data["title"], pull_data["body"]
             ))
             run.add_step(CommentStep(
                 run.servo_pr, UPDATED_TITLE_IN_EXISTING_UPSTREAM_PR))
@@ -258,7 +262,8 @@ class WPTSync:
         if pull_data["merged"]:
             # Since the upstreamable changes have now been merged locally, merge the
             # corresponding upstream PR.
-            run.add_step(MergePRStep(run.upstream_pr.value(), ["do not merge yet"]))
+            run.add_step(MergePRStep(
+                run.upstream_pr.value(), ["do not merge yet"]))
         else:
             # If a PR with upstreamable changes is closed without being merged, we
             # don't want to merge the changes upstream either.
diff --git a/etc/ci/upstream-wpt-changes/wptupstreamer/step.py b/etc/ci/upstream-wpt-changes/wptupstreamer/step.py
index 31ae94b96eb..3c16bf88c81 100644
--- a/etc/ci/upstream-wpt-changes/wptupstreamer/step.py
+++ b/etc/ci/upstream-wpt-changes/wptupstreamer/step.py
@@ -99,8 +99,9 @@ class CreateOrUpdateBranchForPRStep(Step):
     def _get_upstreamable_commits_from_local_servo_repo(self, sync: WPTSync):
         local_servo_repo = sync.local_servo_repo
         number_of_commits = self.pull_data["commits"]
+        pr_head = self.pull_data["head"]["sha"]
         commit_shas = local_servo_repo.run(
-            "log", "--pretty=%H", f"-{number_of_commits}"
+            "log", "--pretty=%H", pr_head, f"-{number_of_commits}"
         ).splitlines()
 
         filtered_commits = []