Add script to update Hermes submodule

Author: huntie

package.json

@@ -40,6 +40,7 @@
     "test-typescript": "dtslint packages/react-native/types",
     "test": "jest",
     "trigger-react-native-release": "node ./scripts/releases-local/trigger-react-native-release.js",
+    "update-hermes": "node ./scripts/update-hermes.js",
     "update-lock": "npx yarn-deduplicate"
   },
   "workspaces": [

scripts/update-hermes.js

@@ -0,0 +1,111 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ * @format
+ * @oncall react_native
+ */
+
+const {REPO_ROOT} = require('./consts');
+const {parseArgs} = require('@pkgjs/parseargs');
+const {execSync} = require('child_process');
+const {promises: fs} = require('fs');
+const path = require('path');
+
+const config = {
+  allowPositionals: true,
+  options: {
+    help: {type: 'boolean'},
+  },
+};
+
+async function main() {
+  const {
+    positionals,
+    values: {help},
+  } = parseArgs(config);
+  let {revision} = positionals;
+
+  if (help) {
+    console.log(`
+  Usage: node ./scripts/update-hermes.js <revision>
+
+  Update the Hermes submodule to the specified Git revision.
+
+  If no Hermes revision is provided, updates to the latest commit on
+  facebook/hermes.
+    `);
+    return;
+  }
+
+  if (revision == null) {
+    console.log(
+      'No revision provided, updating to latest commit on facebook/hermes.',
+    );
+
+    try {
+      revision = getLatestHermesRevision();
+    } catch (e) {
+      console.error('Could not determine latest Hermes revision. Aborting.');
+      process.exitCode = 1;
+      return;
+    }
+  }
+
+  if (revision === getCurrentHermesRevision()) {
+    console.log('Hermes submodule is already up to date. Exiting.');
+    return;
+  }
+
+  console.log(`Updating Hermes submodule to ${revision ?? 'latest'}`);
+
+  if ((await fs.stat(path.join(REPO_ROOT, '.git'))).isDirectory()) {
+    await updateSubmoduleUnderGit(revision);
+  } else {
+    await updateSubmoduleUnderHg(revision);
+  }
+}
+
+function getCurrentHermesRevision() /*: string */ {
+  const stdout = execFromRoot('git -C hermes log -n 1');
+
+  return stdout.toString().split('\n')[0].split(' ')[1];
+}
+
+function getLatestHermesRevision() /*: string */ {
+  const stdout = execFromRoot('git -C hermes log -n 1 origin/main');
+
+  return stdout.toString().split('\n')[0].split(' ')[1];
+}
+
+async function updateSubmoduleUnderGit(revision /*: string */) {
+  const commands = `
+    git submodule update --remote hermes;
+    git -C hermes checkout ${revision};
+    git add hermes;
+    git commit -m "Update Hermes to ${revision.slice(0, 8)}" -m "Changelog: [Internal]";
+  `;
+  commands.split(';').forEach(command => execFromRoot(command));
+}
+
+async function updateSubmoduleUnderHg(revision /*: string */) {
+  await fs.writeFile(
+    path.join(REPO_ROOT, 'hermes.submodule.txt'),
+    `Subproject commit ${revision}\n`,
+  );
+  execFromRoot(
+    `hg commit -m "[RN] Update Hermes to ${revision.slice(0, 8)}" -m "Changelog: [Internal]"`,
+  );
+}
+
+function execFromRoot(command /*: string */, options = {}) {
+  return execSync(command, {cwd: REPO_ROOT, ...options});
+}
+
+if (require.main === module) {
+  // eslint-disable-next-line no-void
+  void main();
+}