ci: Fail when a Playwright version drifts from the pinned one

.github/workflows/build.yml

@@ -346,6 +346,8 @@ jobs:
             run: yarn lint:es-compatibility
           - name: Lint types
             run: yarn lint:types
+          - name: Check Playwright versions
+            run: node ./scripts/check-playwright-versions.mjs
 
   job_check_lockfile:
     name: Check lockfile

scripts/check-playwright-versions.mjs

@@ -0,0 +1,55 @@
+/* eslint-disable no-console */
+import { existsSync, readdirSync, readFileSync } from 'node:fs';
+import { join } from 'node:path';
+
+// Every package, including each E2E app, must use this exact version.
+// `install-playwright` installs browsers for the declared version, so a drifting app would test against other browsers.
+const REFERENCE_PACKAGE_JSON = 'dev-packages/test-utils/package.json';
+const PLAYWRIGHT_PACKAGES = ['@playwright/test', 'playwright', 'playwright-core'];
+const DEPENDENCY_FIELDS = ['dependencies', 'devDependencies', 'peerDependencies', 'optionalDependencies'];
+const PACKAGE_DIRS = ['packages', 'dev-packages', 'dev-packages/e2e-tests/test-applications'];
+
+const rootDir = join(import.meta.dirname, '..');
+
+/** @param {string} path */
+function readPackageJson(path) {
+  return JSON.parse(readFileSync(join(rootDir, path), 'utf8'));
+}
+
+const expected = readPackageJson(REFERENCE_PACKAGE_JSON).devDependencies['@playwright/test'];
+
+if (!/^\d+\.\d+\.\d+$/.test(expected)) {
+  console.error(`@playwright/test in ${REFERENCE_PACKAGE_JSON} must be an exact version, got "${expected}".`);
+  process.exit(1);
+}
+
+const packageJsonPaths = ['package.json'];
+for (const dir of PACKAGE_DIRS) {
+  for (const entry of readdirSync(join(rootDir, dir), { withFileTypes: true })) {
+    const path = join(dir, entry.name, 'package.json');
+    if (entry.isDirectory() && existsSync(join(rootDir, path))) {
+      packageJsonPaths.push(path);
+    }
+  }
+}
+
+const mismatches = [];
+for (const path of packageJsonPaths) {
+  const packageJson = readPackageJson(path);
+  for (const field of DEPENDENCY_FIELDS) {
+    for (const name of PLAYWRIGHT_PACKAGES) {
+      const version = packageJson[field]?.[name];
+      if (version !== undefined && version !== expected) {
+        mismatches.push(`  ${path}: ${field}["${name}"] is "${version}"`);
+      }
+    }
+  }
+}
+
+if (mismatches.length) {
+  console.error(`All Playwright dependencies must be pinned to "${expected}" (from ${REFERENCE_PACKAGE_JSON}):`);
+  console.error(mismatches.join('\n'));
+  process.exit(1);
+}
+
+console.log(`All Playwright dependencies are pinned to ${expected}.`);