Add PR body validation to analyze-pr workflow (#55382)

Summary:
Pull Request resolved: #55382

This adds a `validatePRBody.js` script that checks pull request descriptions for required sections as part of a new `analyze-pr.yml` workflow that will replace part of the Danger-pr workflow.

The validation includes:
- **Description length check**: Fails if the PR body is missing or less than 50 characters
- **Summary section check**: Warns if the PR lacks a "## Summary" section
- **Test plan check**: Warns if the PR lacks a "## Test Plan" section
- **Changelog validation**: failing if missing or invalid

Key behaviors:
- Phabricator-sourced PRs (detected via "Differential Revision:" in body) skip summary, test plan, and changelog validation since these are enforced differently
- Validation messages use GitHub's `[!WARNING]` and `[!CAUTION]` callout syntax for clear visual feedback
- The workflow fails (via `core.setFailed`) when any required check fails
- Messages are passed to `postPRComment` alongside API changes for consolidated PR comments

This aims to mimic relevant parts of dangerfile.js

Changelog: [Internal]

Reviewed By: huntie

Differential Revision: D91158803

fbshipit-source-id: 2304251d18f9fc8bf9a29e536fff2d979573bd86

Author: emily8rown

.github/workflow-scripts/validatePRBody.js

@@ -0,0 +1,102 @@
+/**
+ * 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.
+ *
+ * @format
+ */
+
+'use strict';
+
+const changelogRegex =
+  /\[\s?(ANDROID|GENERAL|IOS|INTERNAL)\s?\]\s?\[\s?(BREAKING|ADDED|CHANGED|DEPRECATED|REMOVED|FIXED|SECURITY)\s?\]\s*?-?\s*?(.*)/i;
+
+const internalChangelogRegex = /\[\s?(INTERNAL)\s?\].*/gi;
+
+function validateChangelog(commitMsg) {
+  if (!commitMsg.toLowerCase().includes('changelog:')) {
+    return 'missing';
+  }
+  const hasValidChangelog = changelogRegex.test(commitMsg);
+  const hasValidInternalChangelog = internalChangelogRegex.test(commitMsg);
+
+  if (hasValidChangelog || hasValidInternalChangelog) {
+    return 'valid';
+  }
+
+  return 'invalid';
+}
+
+function validatePRBody(prBody) {
+  const body = prBody ?? '';
+  const bodyLower = body.toLowerCase();
+  const isFromPhabricator = bodyLower.includes('differential revision:');
+
+  const messages = [];
+  let hasFail = false;
+
+  function addWarning(title, text) {
+    messages.push(`> [!WARNING]
+> **${title}**
+>
+> ${text}`);
+  }
+
+  function addFail(title, text) {
+    hasFail = true;
+    messages.push(`> [!CAUTION]
+> **${title}**
+>
+> ${text}`);
+  }
+
+  if (!body || body.length < 50) {
+    addFail('Missing Description', 'This pull request needs a description.');
+  } else {
+    const hasSummary =
+      bodyLower.includes('## summary') || bodyLower.includes('summary:');
+    if (!hasSummary && body.split('\n').length <= 2 && !isFromPhabricator) {
+      addWarning(
+        'Missing Summary',
+        'Please add a "## Summary" section to your PR description. This is a good place to explain the motivation for making this change.',
+      );
+    }
+  }
+
+  if (!isFromPhabricator) {
+    const hasTestPlan = ['## test plan', 'test plan:', 'tests:', 'test:'].some(
+      t => bodyLower.includes(t),
+    );
+    if (!hasTestPlan) {
+      addWarning(
+        'Missing Test Plan',
+        'Please add a "## Test Plan" section to your PR description. A Test Plan lets us know how these changes were tested.',
+      );
+    }
+  }
+
+  if (!isFromPhabricator) {
+    const status = validateChangelog(body);
+    const link =
+      'https://reactnative.dev/contributing/changelogs-in-pull-requests';
+    if (status === 'missing') {
+      addFail(
+        'Missing Changelog',
+        `Please add a Changelog to your PR description. See [Changelog format](${link})`,
+      );
+    } else if (status === 'invalid') {
+      addFail(
+        'Invalid Changelog Format',
+        `Please verify your Changelog format. See [Changelog format](${link})`,
+      );
+    }
+  }
+
+  return {
+    message: messages.join('\n\n'),
+    status: hasFail ? 'FAIL' : 'PASS',
+  };
+}
+
+module.exports = validatePRBody;

.github/workflows/analyze-pr.yml

@@ -0,0 +1,37 @@
+name: Analyze Pull Request
+
+on:
+  pull_request_target:
+    types: [opened, edited, reopened, synchronize]
+
+permissions:
+  pull-requests: write
+
+jobs:
+  analyze-pr:
+    runs-on: ubuntu-latest
+    if: github.repository == 'facebook/react-native'
+    steps:
+      - name: Check out main branch
+        uses: actions/checkout@v6
+      - name: Setup Node.js
+        uses: ./.github/actions/setup-node
+      - name: Run yarn install
+        uses: ./.github/actions/yarn-install
+      - name: Check PR body
+        id: check-pr-body
+        uses: actions/github-script@v8
+        with:
+          script: |
+            const validatePRBody = require('./.github/workflow-scripts/validatePRBody.js');
+            const {message, status} = validatePRBody(context.payload.pull_request.body);
+            core.setOutput('message', message);
+            core.setOutput('status', status);
+      - name: Post PR comment
+        uses: ./.github/actions/post-pr-comment
+        with:
+          marker: '<!-- analyze-pr -->'
+          sections: '[${{ toJSON(steps.check-pr-body.outputs.message) }}]'
+      - name: Fail if validation errors
+        if: steps.check-pr-body.outputs.status == 'FAIL'
+        run: exit 1