Add vendor integrity check

cloudbuild.yaml

@@ -21,6 +21,9 @@ steps:
         #   entrypoint: sh
         #   # deploys folder of test results (with build id as folder name) to GCS
         #   args: ['-c', 'gsutil cp -r $(cat _DATE) gs://cel-conformance/test-logs/']
+        - name: 'ubuntu'
+          # check the integrity of the vendor directory
+          args: ['scripts/verify-vendor.sh']
         - name: 'gcr.io/cloud-builders/bazel'
           entrypoint: bazel
           args: ['test', '--test_output=errors', '...']

scripts/verify-vendor.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+tmp="$(mktemp -d)"
+go mod vendor -o "$tmp"
+if ! _out="$(diff -Naupr vendor $tmp)"; then
+  echo "Verify vendor failed" >&2
+  echo "If you're seeing this locally, run the below command to fix your go.mod:" >&2
+  echo "go mod vendor" >&2
+  exit 1
+fi