Add branch targeting check to analyze-pr workflow (#55383)

Summary:
Pull Request resolved: #55383

Adds a branch targeting validation that replaces the equivalent Danger.js check.
  The check validates that PRs target either `main` or a `-stable` branch, and
  automatically adds the "Pick Request" label when targeting stable branches.

  - Created `checkBranchTarget.js` - pure function returning validation message
  - Added check step to `annotate-pr.yml` that calls the JS and adds labels
  - Added `issues: write` permission for label functionality

Changelog: [Internal]

Reviewed By: huntie

Differential Revision: D91685081

fbshipit-source-id: 87e7124f7d825b51cb791dc94720c487ff95d414

Author: emily8rown

.github/workflow-scripts/checkBranchTarget.js

@@ -0,0 +1,40 @@
+/**
+ * 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';
+
+/**
+ * Validates that the PR targets an appropriate base branch.
+ *
+ * @param {string} baseRef - The base branch ref (e.g., 'main', '0.76-stable')
+ * @returns {{message: string, status: 'PASS'|'FAIL', shouldAddPickLabel: boolean}}
+ */
+function checkBranchTarget(baseRef) {
+  const isMain = baseRef === 'main';
+  const isStable = baseRef.endsWith('-stable');
+
+  let message = '';
+  let status = 'PASS';
+  if (!isMain && !isStable) {
+    status = 'FAIL';
+    message = `> [!CAUTION]
+> **Invalid Base Branch**
+>
+> The base branch for this PR is \`${baseRef}\`, which is not \`main\` or a \`-stable\` branch.
+> [Are you sure you want to target this branch?](https://reactnative.dev/docs/contributing#pull-requests)`;
+  }
+
+  return {
+    message,
+    status,
+    shouldAddPickLabel: isStable,
+  };
+}
+
+module.exports = checkBranchTarget;

.github/workflows/analyze-pr.yml

@@ -6,6 +6,7 @@ on:
 
 permissions:
   pull-requests: write
+  issues: write
 
 jobs:
   analyze-pr:
@@ -25,13 +26,33 @@ jobs:
           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: Check branch target
+        id: check-branch-target
+        uses: actions/github-script@v8
+        with:
+          script: |
+            const checkBranchTarget = require('./.github/workflow-scripts/checkBranchTarget.js');
+            const baseRef = context.payload.pull_request.base.ref;
+            const {message, status, shouldAddPickLabel} = checkBranchTarget(baseRef);
+
+            if (shouldAddPickLabel) {
+              await github.rest.issues.addLabels({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: context.issue.number,
+                labels: ['Pick Request'],
+              });
+            }
+
             core.setOutput('message', message);
             core.setOutput('status', status);
       - name: Post PR comment
         uses: ./.github/actions/post-pr-comment
         with:
           marker: '<!-- analyze-pr -->'
-          sections: '[${{ toJSON(steps.check-pr-body.outputs.message) }}]'
+          sections: '[${{ toJSON(steps.check-pr-body.outputs.message) }}, ${{ toJSON(steps.check-branch-target.outputs.message) }}]'
       - name: Fail if validation errors
-        if: steps.check-pr-body.outputs.status == 'FAIL'
+        if: steps.check-pr-body.outputs.status == 'FAIL' || steps.check-branch-target.outputs.status == 'FAIL'
         run: exit 1