Create stale.yml workflow to label stale PRs (#13565)

The behavior is:
- If a PR is not labeled stale, after 60 days inactivity label the PR as
stale and comment about it.
- If a PR is labeled stale, after 30 days inactivity close the PR.
- `high priority` and `no-stale` PRs are exempt.

Author: nil-is-all

.github/workflows/stale

@@ -0,0 +1,149 @@
+# The behavior is:
+# - If a PR is not labeled stale, after 60 days inactivity label the PR as stale and comment about it.
+# - If a PR is labeled stale, after 30 days inactivity close the PR.
+# - `high priority` and `no-stale` PRs are exempt.
+
+name: Close stale pull requests
+
+on:
+  schedule:
+    # Run daily at 00:30 UTC.
+    - cron: '30 0 * * *'
+  workflow_dispatch:
+
+jobs:
+  stale:
+    if: ${{ github.repository == 'pytorch/executorch' }}
+    runs-on: linux.large
+    permissions:
+      contents: read
+      pull-requests: write
+
+    steps:
+      - uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
+        with:
+          script: |
+            // Do some dumb retries on requests.
+            const retries = 7;
+            const baseBackoff = 100;
+            const sleep = timeout => new Promise(resolve => setTimeout(resolve, timeout));
+            github.hook.wrap('request', async (request, options) => {
+              for (let attempt = 1; attempt <= retries; attempt++) {
+                try {
+                  return await request(options);
+                } catch (err) {
+                  if (attempt < retries) {
+                    core.warning(`Request getting retried. Attempt: ${attempt}`);
+                    await sleep(baseBackoff * Math.pow(2, attempt));
+                    continue;
+                  }
+                  throw err;
+                }
+              }
+            });
+
+            const MAX_API_REQUESTS = 100;
+
+            // If a PRs not labeled stale, label them stale after no update for 60 days.
+            const STALE_LABEL_THRESHOLD_MS = 1000 * 60 * 60 * 24 * 60;
+            // For PRs already labeled stale, close after not update for 30 days.
+            const STALE_CLOSE_THRESHOLD_MS = 1000 * 60 * 60 * 24 * 30;
+
+            const STALE_MESSAGE =
+              "Looks like this PR hasn't been updated in a while so we're going to go ahead and mark this as `Stale`. <br>" +
+              "Feel free to remove the `Stale` label if you feel this was a mistake. <br>" +
+              "If you are unable to remove the `Stale` label please contact a maintainer in order to do so. <br>" +
+              "If you want the bot to never mark this PR stale again, add the `no-stale` label.<br>" +
+              "`Stale` pull requests will automatically be closed after 30 days of inactivity.<br>";
+
+            let numAPIRequests = 0;
+            let numProcessed = 0;
+
+            async function processPull(pull) {
+              core.info(`[${pull.number}] URL: ${pull.html_url}`);
+              numProcessed += 1;
+              const labels = pull.labels.map((label) => label.name);
+
+              // Skip if certain labels are present.
+              if (labels.includes("no-stale") || labels.includes("high priority")) {
+                core.info(`[${pull.number}] Skipping because PR has an exempting label.`);
+                return false;
+              }
+
+              // Check if the PR is stale, according to our configured thresholds.
+              let staleThresholdMillis;
+              if (labels.includes("Stale")) {
+                core.info(`[${pull.number}] PR is labeled stale, checking whether we should close it.`);
+                staleThresholdMillis = STALE_CLOSE_THRESHOLD_MS;
+              } else {
+                core.info(`[${pull.number}] Checking whether to label PR as stale.`);
+                staleThresholdMillis = STALE_LABEL_THRESHOLD_MS;
+              }
+
+              const millisSinceLastUpdated =
+                new Date().getTime() - new Date(pull.updated_at).getTime();
+
+              if (millisSinceLastUpdated < staleThresholdMillis) {
+                core.info(`[${pull.number}] Skipping because PR was updated recently`);
+                return false;
+              }
+
+              // At this point, we know we should do something.
+              // For PRs already labeled stale, close them.
+              if (labels.includes("Stale")) {
+                core.info(`[${pull.number}] Closing PR.`);
+                numAPIRequests += 1;
+                  //await github.rest.issues.update({
+                  //owner: "pytorch",
+                  //repo: "executorch",
+                  //issue_number: pull.number,
+                  //state: "closed",
+                  //});
+              } else {
+                // For PRs not labeled stale, label them stale.
+                core.info(`[${pull.number}] Labeling PR as stale.`);
+
+                numAPIRequests += 1;
+                  //await github.rest.issues.createComment({
+                  //owner: "pytorch",
+                  //repo: "executorch",
+                  //issue_number: pull.number,
+                  //body: STALE_MESSAGE,
+                //});
+
+                numAPIRequests += 1;
+                  //await github.rest.issues.addLabels({
+                  //owner: "pytorch",
+                  //repo: "executorch",
+                  //issue_number: pull.number,
+                  //labels: ["Stale"],
+                //});
+              }
+            }
+
+            for await (const response of github.paginate.iterator(
+              github.rest.pulls.list,
+              {
+                owner: "pytorch",
+                repo: "executorch",
+                state: "open",
+                sort: "created",
+                direction: "asc",
+                per_page: 100,
+              }
+            )) {
+              numAPIRequests += 1;
+              const pulls = response.data;
+              // Awaiting in a loop is intentional here. We want to serialize execution so
+              // that log groups are printed correctl
+              for (const pull of pulls) {
+                if (numAPIRequests > MAX_API_REQUESTS) {
+                  core.warning("Max API requests exceeded, exiting.");
+                  process.exit(0);
+                }
+                await core.group(`Processing PR #${pull.number}`, async () => {
+                  await processPull(pull);
+                });
+              }
+            }
+            core.info(`Processed ${numProcessed} PRs total.`);